Microbiology: Antimicrobials Flashcards
What are the antiprotozoal agents of choice for Trypanosoma brucei infection?
Suramin, melarsoprol
What are the possible adverse effects of carbapenem class of antibiotics?
Carbapenems can cause CNS toxicity and seizures at high plasma levels, GI problems, and skin rash
What 2 common adverse effects of metronidazole are NOT associated with alcohol use?
Headache and metallic taste
A patient with AIDS presents with Cushing-like syndrome secondary to use of one of his HIV medications. What is the mechanism of action of the culprit drug?
It stops viral maturation by preventing formation of polypeptide products; this is a protease inhibitor “Navir [never] tease a protease”
What is the common renal manifestation of sulfonamide toxicity?
Tubulointerstitial nephritis
Which types of organisms are treated with vancomycin?
Gram ⊕ only: MRSA, Staphylococcus epidermidis, Enterococcus spp, Clostridium difficile (oral dosing for pseudomembranous colitis)
A patient’s infection is no longer susceptible to tetracycline treatment. What mechanism mediated this resistance?
↓ uptake into bacterial cells or ↑ efflux out of cells by plasmid-encoded transport pumps
Why does acyclovir interfere with viral DNA synthesis and not human DNA synthesis?
It requires monophosphorylation by the thymidine kinase of herpes simplex virus/varicella-zoster virus and is inactive in uninfected cells
Which processes do sulfonamides and trimethoprim (TMP) affect to exert their antibacterial effects?
Folic acid synthesis and reduction (DNA methylation); sulfonamides inhibit PABA to DHF conversion; TMP inhibits conversion of DHF to THF
A patient with well-treated depression has MRSA pneumonia, which is treated with linezolid. Which serious adverse effect might you worry about?
Serotonin syndrome; more likely to occur if a patient is also taking a selective serotonin-reuptake inhibitor (due to partial monoamine oxidase [MAO] inhibition)
Name the antifungal agent that deposits in keratin-containing tissues, making it effective against dermatophyte infections.
Griseofulvin
A patient being treated for severe multidrug-resistant Eshcerichia coli infection develops slurred speech and weakness. For what other symptoms would you monitor?
Nephrotoxicity and respiratory failure; this patient has neurotoxicity from polymyxin use
Nucleoside reverse transcriptase inhibitors (NRTIs) are a class of HIV drugs that inhibit reverse transcriptase. What is a common suffix for this class of drugs?
-ine: didanosine, emtricitabine, lamivudine, stavudine, zidovudine; others are abacavir and tenofovir
Macrolides are used to treat infection with which organisms?
Gram ⊕ cocci, Mycoplasma, Legionella, Chlamydia, and Bordetella pertussis
Via what receptor does interferon-α act to exert its antiviral effects?
The PKR receptor
Acyclovir and valacyclovir are good therapeutic options against herpes simplex virus and varicella-zoster virus. Which common herpes viruses are they not useful against?
Epstein-Barr virus (weak activity), cytomegalovirus (no activity)
Deficiency of which enzyme is to blame for premature infants developing gray baby syndrome after receiving chloramphenicol?
UDP-glucuronosyltransferase, which premature infants lack
Gynecomastia develops in a man being treated for systemic mycoses. What is the cause of the adverse effect?
Inhibition of testosterone synthesis by an azole (most commonly seen with ketoconazole)
Which antifungal drug class kills fungi by causing the formation of membrane pores and disrupting cell membrane integrity?
The polyenes (amphotericin B and nystatin)
Which types of influenza are oseltamivir and zanamivir effective against?
Influenza A and B (for treatment and prevention)
What is the mechanism of action of isoniazid?
↓ synthesis of mycolic acids, which make up the cell wall
What is the activity of acyclovir, famciclovir, and valacyclovir against latent varicella-zoster virus or herpes simplex virus?
Minimal; these drugs work best in actively infected cells only
Why are ampicillin and amoxicillin considered extended-spectrum penicillins?
They cover Haemophilus influenzae, Helicobacter pylori, Escherichia coli, Listeria monocytogenes, Proteus mirabilis, Salmonella, and Shigella (HHELPSS kill enterococci)
A man has shingles. Which antiviral agent is the most appropriate therapeutic option?
Famciclovir (more effective against herpes zoster than acyclovir or valacyclovir)
Which disinfection and sterilization techniques are sporicidal?
Autoclaving, chlorine, ethylene oxide, hydrogen peroxide, iodine and iodophors (may be sporicidal)
A patient being treated for malaria complains of blurry vision. What is the most likely cause?
Chloroquine-induced retinopathy
What organisms are aminoglycosides used against?
Gram ⊖ rods, particularly in cases of severe infection
Antibiotics that target bacteria via their cell walls typically do so by interfering with the production of which cell wall component?
Peptidoglycans
What is the mechanism of action of azoles?
They block fungal synthesis of sterols (ergosterol) by inhibiting P-450 enzymes from converting lanosterol to ergosterol
Which antifungal drug class works by inhibiting the synthesis of fungal cell walls?
The echinocandins (anidulafungin, caspofungin, and micafungin)
What is the mechanism by which bacteria develop resistance to macrolide antibiotics?
By methylation of the 23S ribosomal RNA binding site, which prevents the drug from binding to it
Polymyxins are used to treat which types of infections?
Last resort treatment for multidrug-resistant gram ⊖ bacterial infections and topical treatment for superficial skin infections
A young woman has chronic hepatitis C and takes an antiviral agent that competitively inhibits IMP dehydrogenase. What are the adverse effects of the antiviral agent she is taking?
Hemolytic anemia and severe teratogenicity (the drug is ribavirin)
A patient with a Mycobacterium leprae infection is concerned about infecting family members. What prophylactic agent can you prescribe for them?
There is no prophylaxis available for M leprae infection
Sulfonamides are bacteriostatic when used alone but addition of which antibiotic can cause sulfonamides to be bactericidal?
Trimethoprim, a dihydrofolate reductase inhibitor
What adverse effects are associated with cephalosporin use?
Hypersensitivity reaction, disulfiram-like reaction, autoimmune hemolytic anemia, vitamin K deficiency
A patient who started treatment for lepromatous leprosy presents with sudden-onset cyanosis and hypoxia. What is your diagnosis?
Methemoglobinemia; the patient was likely started on dapsone
What monotherapy can be used for chronic hepatitis C infection?
None, treatment is always with a combination of drugs
What are some of the adverse reactions associated with vancomycin?
Nephrotoxicity, Ototoxicity, Thrombophlebitis (NOT trouble free), red man and DRESS syndromes
A patient taking an antimycobacterial agent has elevated liver enzymes and certain drug interactions. What is the mechanism by which this occurs?
Increased cytochrome P-450 activity due to rifampin
After a patient starts therapy for tuberculosis, he notices that his shirt is stained with orange sweat. What is the explanation for this phenomenon?
This is a benign adverse effect of Rifampin (Red/orange body fluids)
A woman being treated for mucocutaneous herpes simplex virus develops acute flank pain and nausea. She reports low oral intake due to painful oral lesions. What has happened?
She has developed acyclovir-induced obstructive crystalline nephropathy (likely due to inadequate hydration from poor oral intake)
A man’s herpes simplex virus infection does not respond to acyclovir, and he refuses foscarnet due to the seizure risk. What drug can you try next?
Cidofovir (given for acyclovir-resistant HSV)
What is the mechanism of resistance to ampicillin and amoxicillin?
Bacterial penicillinase cleaves the β-lactam ring (avoid this by coprescribing clavulanic acid, which inhibits penicillinases)
Name 6 antibiotics that can be used to treat methicillin-resistant Staphylococcus aureus (MRSA).
Vancomycin, daptomycin, linezolid, tigecycline, ceftaroline, doxycycline
Phlebitis develops in a patient being treated for mucor. Which antifungal agent is the most likely cause?
Amphotericin B (“amphoterrible”)
Aztreonam is usually well tolerated, but which adverse effect do patients occasionally have?
Gastrointestinal upset
Use of amphotericin B requires supplementation with which electrolytes?
Potassium and magnesium (due to altered renal tubule permeability)
Name the 4 carbapenem antibiotics.
Doripenem, Imipenem, Meropenem, and Ertapenem (DIME antibiotics are given when there is a 10/10 [life-threatening] infection)
What is the mechanism of action of the rifamycins, rifabutin and rifampin?
They block mRNA synthesis via inhibition of DNA-dependent RNA polymerase
What 2 adverse effects are caused by efavirenz?
CNS symptoms and vivid dreams
What is the advantage of using valacyclovir over acyclovir?
Valacyclovir is a prodrug of acyclovir with better oral bioavailability
Addition of a certain bactericidal antibiotic leads to misreading of the mRNA. Inhibition of which ribosomal subunit is likely the cause?
30S ribosomal unit (blocked by aminoglycosides and can cause misreading of mRNA)
A premature infant in Western Africa develops grayish skin after receiving a certain antibiotic. What is the mechanism of action of the antibiotic given?
Inhibits peptidyltransferase activity in the 50S subunit of the ribosome; the drug administered was chloramphenicol
How does adjusting the dose of the antibiotic chloramphenicol influence its risk of causing anemia?
Lowering the dose will lower the risk of anemia, as chloramphenicol-induced anemia is a dose-dependent adverse effect of the drug
Which antifungal agent is primarily used to treat onychomycosis?
Terbinafine
How do bacteria develop resistance to vancomycin?
Conversion of D-Ala-D-Ala to D-Ala-D-Lac; (if you Lack a D-Ala (dollar), you can’t ride the van [vancomycin])
What is the most serious adverse effect of flucytosine?
Bone marrow suppression
How does daptomycin exert its antibacterial effects?
It interferes with membrane integrity
A patient with renal failure needs a tetracycline-class drug for treatment of a Mycoplasma pneumoniae infection. What do you prescribe and why?
Doxycycline; it is fecally eliminated and can be used by patients with renal failure
A patient in renal failure needs to start antiretroviral therapy (ART) for newly diagnosed HIV. Which protease inhibitor should not be given to him?
Indinavir, which can cause nephropathy and hematuria
What are some of the dermatological manifestations of sulfonamide toxicity?
Photosensitivity or Stevens-Johnson syndrome
Clindamycin is used to treat anaerobic infections above the diaphragm. Which antimicrobial is used to treat infections below the diaphragm?
Metronidazole
What advantage does the prodrug of ganciclovir have?
Better oral bioavailability; the prodrug is valganciclovir
What is the mechanism of action of cidofovir?
Inhibits viral DNA polymerase; unlike guanosine analogs, it does not require phosphorylation by viral kinases
The peptidyl transferase activity is ↓ in bacteria after having given a certain 50S-inhibiting antibiotic. Identify the antibiotic.
Chloramphenicol
What is the mechanism of action of fluoroquinolones?
They inhibit prokaryotic topoisomerase II (DNA gyrase) and topoisomerase IV; they are bactericidal
Name the peptidoglycan cross-linking, inhibiting antibiotics that are penicillinase sensitive.
Penicillin G and V, ampicillin, amoxicillin
At what point during disease progression is imipenem or meropenem considered?
When other medications have failed or in life-threatening infections; they have significant adverse effects
Name the 4 non-respiratory fluoroquinolones.
Ciprofloxacin, norfloxacin, ofloxacin, and enoxacin
Describe the mechanism of action of the bacteriostatic macrolide antibiotics.
They inhibit protein synthesis by binding to the 23S rRNA of the 50S subunit and preventing translocation (macroslides)
An HIV antiviral drug prevents viral penetration. This ultimately blocks which genetic process immediately downstream of penetration?
Uncoating and reverse transcription (the drug is the fusion inhibitor enfuvirtide)
You treat a patient with an extended-spectrum β-lactam for a pseudomonal infection. What must be coadministered to overcome antibiotic resistance?
A β-lactamase inhibitor
A patient being treated for tinea corporis complains of headache and confusion. What is the most likely cause?
Griseofulvin
What is the general indication for treatment or prophylaxis with azoles?
For local and less serious systemic mycoses
How do penicillins, antipseudomonals, cephalosporins, carbapenems, and monobactams work?
They block cell wall synthesis by inhibiting cross-linking of peptidoglycans
What is the common dermatologic adverse effect of fluoroquinolones?
Rash
How does the antifungal drug that inhibits squalene epoxidase affect the concentration of ergosterol?
It will ↓ the level of ergosterol by ↓ lanosterol concentration available for 14-α-demethylase to convert into ergosterol
What are some potential adverse effects of daptomycin?
Rhabdomyolysis, myopathy
What antibiotic classically causes gray baby syndrome if taken by a pregnant woman?
Chloramphenicol
Contrast the modes of administration for penicillin G and penicillin V.
Penicillin G is administered intravenously or intramuscularly; penicillin V is administered orally
A man with sepsis receiving an aminoglycoside shows worsening renal function after receiving another drug. Which drug was added?
A cephalosporin (when combined with aminoglycosides, cephalosporins ↑ the potential for nephrotoxicity)
What are the 3 major adverse effects of ampicillin and amoxicillin?
Rash, hypersensitivity reaction, pseudomembranous colitis
Aztreonam is active against which organisms?
Gram ⊖ rods only
What is the mechanism of action of permethrin?
Blockage of sodium channels leading to depolarization of the neuronal membrane
A mutation in which enzyme allows cytomegalovirus and herpes simplex virus to be resistant to foscarnet?
DNA polymerase
A man’s cytomegalovirus infection is noted to have mutated viral kinases on genetic analysis. How does this influence the use of foscarnet as a treatment?
It has no influence; foscarnet does not require activation by viral kinases, and its efficacy will not be affected
What antifungal drug class works by inhibiting ergosterol synthesis?
Azoles (clotrimazole, fluconazole, itraconazole, ketoconazole, miconazole, and voriconazole)
Which aspect of nafcillin makes it resistant to degradation by the bacterial β-lactamase?
Bulky R group blocks access of β-lactamase to the β-lactam ring of the antibiotic
What are the 2 adverse effects of echinocandins?
Gastrointestinal upset and flushing
Which organisms are covered by the first-generation cephalosporins?
Gram ⊕ cocci (such as Staphylococcus auerus), Proteus mirabilis, Eschericia coli, Klebsiella pneumoniae (⊕ PEcK)
A patient receiving a new HIV drug regimen has had several skin reactions at the site of injection. What drug was she prescribed?
Enfuvirtide
Name the drug that is a monobactam.
Aztreonam
A patient has a severe gram ⊖ organism infection. Why do you choose to treat with aminoglycosides and a monobactam?
Aztreonam, a monobactam, is synergistic with aminoglycosides
A patient has a Sarcoptes scabiei infection. Which anti-mite/louse agents may be used?
Treat PML (Pesty Mites and Lice) with PML (Permethrin, Malathion, Lindane) because they NAG you (Na, AChE, GABA blockade)
Name the 2 fungal infections that are treated with isavuconazole?
Serious Aspergillus or Mucor infections
A man presents with low hemoglobin soon after starting on sulfadiazine. Which underlying enzyme deficiency does he likely have?
G6PD deficiency, causing hemolytic anemia
Name the 2 antibiotics that belong to the polymyxin class.
Colistin (polymyxin E) and polymyxin B
A patient with otitis externa is on an antibiotic that inhibits DNA gyrase. By what mechanisms can the bacteria develop resistance to the drug?
Chromosome-encoded mutation in the bacterial DNA gyrase, efflux pumps, or resistance mediated by plasmids; the patient is on a fluoroquinolone
What is the difference between disinfection and sterilization?
Disinfection reduces the number of pathogenic organisms to a safe level; sterilization inactivates all microbes (including spores)
What is the mechanism of action of dapsone?
It inhibits dihydropteroate synthase (sulfonamides inhibit the same enzyme), impairing bacterial folate synthesis
A man has a severe gram ⊖ infection that has been resistant to previously prescribed β-lactams. What do you prescribe next?
A third-generation cephalosporin (ceftriaxone, cefotaxime, cefpodoxime, or ceftazidime)
Which drug treats hepatitis C virus (HCV) by inhibiting HCV RNA-dependent RNA polymerase?
Sofosbuvir or dasabuvir (both cause viral RNA chain termination)
What is the mechanism of action of pyrazinamide?
Unclear; it acts via an unknown mechanism intracellularly
While prescribing antiretroviral therapy (ART), you discover that your patient has an HLA-B*5701 mutation. What drug is contraindicated?
Abacavir (nucleoside reverse transcriptase inhibitor [NRTI]) due to the ↑ risk of hypersensitivity
What is the mechanism of action of the antifungal agent terbinafine?
It inhibits squalene epoxidase (converts squalene into squalene epoxide), which ultimately blocks the production of lanosterol
When drug X, which is metabolized by P-450, is given to patients on treatment for tuberculosis, the serum levels are higher than expected. Identify the culprit.
Isoniazid; it is an inhibitor of cytochrome P-450
What is the mechanism by which bacteria develop resistance to aminoglycosides?
Transferase enzymes inactivate the drug by acetylation, phosphorylation, or adenylation
Which antibiotic is given to newborns as prophylaxis against gonococcal conjunctivitis?
Erythromycin ointment applied to the eyes
What is the mechanism of action of maraviroc?
Binds CCR-5 on T cells/monocytes, inhibiting CCR-5 interaction w/gp120; (maraviroc inhibits docking)
For hepatitis C infections refractory to newer therapies, what agent can be administered as an adjunct?
Ribavirin
Name 2 antibiotics that can be used against multidrug-resistant Pseudomonas aeruginosa and Acinetobacter baumannii.
Polymyxins B and E (colistin)
How does resistance to acyclovir occur?
Mutated viral thymidine kinase
How are sulfonamides and dapsone similar?
They both inhibit folate synthesis by blocking dihydropteroate synthase
Name an antifungal agent that works by inhibiting nucleic acid synthesis.
Flucytosine
A drug is added to influenza-infected cells. Formed viral progeny become trapped within the cell. This is due to inhibition of which enzyme?
Neuraminidase (the drug is likely a neuraminidase inhibitor, such as oseltamivir or zanamivir, which blocks progeny virus release from the cell)
A patient taking an intravenous antibiotic for Clostridium difficile notices a metallic taste. Which antibiotic is it?
Metronidazole
What is the common gastrointestinal adverse effect of fluoroquinolones?
Gastrointestinal upset
A patient experiences taste disturbances after being treated for a fungal infection of his toenails. What is the drug’s mechanism of action?
Inhibits squalene epoxidase (in fungi)
What are the potential adverse effects of tigecycline?
Gastrointestinal distress, including nausea and vomiting
What is the mechanism by which bacteria develop resistance to carbapenems?
Via carbapenemases, typically produced by Klebsiella pneumoniae, Eshcerichia coli, and Enterobacter aerogenes
A pregnant woman is found to be HIV ⊕ and asks about drug options to help protect her child. Which nucleoside reverse transcriptase inhibitor (NRTI) may be used?
Zidovudine (ZDV) can ↓ the risk of vertical transmission and is also used for general prophylaxis
Why is daptomycin ineffective against MRSA pneumonia?
Daptomycin binds to and is inactivated by surfactant before it can act on the lungs
How does adjusting the dose of the antibiotic chloramphenicol influence its risk of causing pancytopenia?
It has no effect because aplastic anemia is a dose-independent adverse effect of chloramphenicol
What is the mechanism of action of malathion?
It inhibits mite/louse acetylcholinesterases
Name 5 antibiotics that work by binding to the bacterial 50S ribosomal subunits and blocking protein synthesis.
Chloramphenicol, clindamycin, streptogramins (quinupristin/dalfopristin), linezolid, macrolides (azithromycin/clarithromycin/erythromycin)
A man on gentamicin is recently started on a new medication. He soon develops hearing loss. Which drug was added?
Likely a loop diuretic, which ↑ the ototoxic potential of aminoglycosides
What is the major reason for the limited use of chloramphenicol in the United States?
High level of toxicity (although still widely used in developing countries due to low cost)
What is the mechanism of action of the anti-hepatitis C virus drugs simeprevir and grazoprevir?
Inhibition of HCV protease (NS3/4A), thereby preventing viral replication
A patient taking a β-lactam drug with reduced penicillinase susceptibility develops a prolonged prothrombin time. Why?
Cephalosporin use can lead to vitamin K deficiency, leading to ↓ clotting factors
A patient being treated with clindamycin develops pseudomembranous colitis. How did this happen?
Clindamycin kills normal gut bacterial flora and allows for the overgrowth of Clostridium difficile
What is the mechanism of action of the drug of choice for non-falciparum malaria?
Blockage of detoxification of heme into hemozoin, causing accumulation of heme, which is toxic to Plasmodium; the drug is chloroquine
A patient starts treatment for CMV with a guanosine analog. Soon after, blood tests show a rising BUN and creatinine. What is the most likely cause of these lab findings?
Ganciclovir-induced renal toxicity
Which anti-malarial agents should be administered to patients with life-threatening malaria infections?
Quinidine in the US (quinine in other countries) or artesunate
Aminoglycosides are synergistic w/which class of antibiotics?
β-lactams
What prophylactic antibiotic is used for patients with prosthetic heart valves undergoing dental procedures?
Amoxicillin; for patients with high risk for endocarditis
A 55-year-old man with epilepsy is started on ciprofloxacin for a UTI. Why might this be a potential problem?
Most antiepileptics are metabolized by the cytochrome P-450 system, which is inhibited by ciprofloxacin
Why are trimethoprim and sulfamethoxazole used in combination?
To synergistically inhibit folate metabolism and thus DNA synthesis, leading to bacterial death instead of growth suppression
A patient taking prednisone is given an antibiotic and develops tendon rupture as a complication. What abnormal finding might you see on his ECG?
A prolonged QT interval; the antibiotic given was a fluoroquinolone, which may cause tendon rupture when combined with prednisone
A 35-year-old hiker from Connecticut has a “bulls-eye” rash on his arm. You prescribe an antibiotic and caution him against consuming what?
Milk, antacids, and iron-containing products; divalent cations inhibit the absorption of tetracyclines
A patient being treated for ringworm experiences flushing, tachycardia, and hypotension after a bachelor party. What drug interaction occurred?
Alcohol, and griseofulvin caused a disulfiram-like reaction
Name the 3 respiratory fluoroquinolones.
Levofloxacin, moxifloxacin, and gemifloxacin
Which feature of tetracyclines makes them effective against Rickettsia and Chlamydia infections?
Their ability to accumulate intracellularly
What is the mechanism of action of cephalosporin antibiotics?
They are bacteriocidal β-lactams that inhibit cell wall synthesis
What are the 3 different mechanisms by which bacteria develop resistance against sulfonamides?
Altered bacterial dihydropteroate synthase, ↓ uptake, or ↑ PABA synthesis
A patient has liver dysfunction after being treated for an Aspergillus infection. What is the mechanism for liver dysfunction?
Azoles inhibit cytochrome P-450
You prescribe metronidazole and advise the patient to avoid alcohol use. Why?
Metronidazole with alcohol causes a disulfiram-like reaction (severe flushing, hypotension, tachycardia)
What is unique regarding the presentation of seizures induced by isoniazid toxicity?
Seizures caused by isoniazid toxicity are refractory to benzodiazepines
What is the mechanism of action of aminoglycosides?
They are bactericidal antibiotics that irreversibly inhibit the initiation complex by binding 30S, blocking translocation, and causing misreading of mRNA
A woman was prescribed an antibiotic during pregnancy. Her baby has hearing abnormalities as a result. Which class of drug was it?
An aminoglycoside
What is the mechanism of action of ampicillin and amoxicillin?
Blockage of bacterial cell wall synthesis through inhibition of peptidoglycan cross-linking (same as penicillin)
What are the adverse effects associated with pyrazinamide?
Hyperuricemia and hepatotoxicity
Which process does rifampin block to exert antimicrobial effects?
The synthesis of bacterial messenger RNA (mRNA) via inhibiting RNA polymerase
Why do patients require different dosages of isoniazid?
People are either fast or slow acetylators, and the half-life of isoniazid differs depending on the individual rate of acetylation
What is key for zanamivir and oseltamivir to be effective in shortening the duration of influenza symptoms?
Initiation of therapy within 48 hours of symptom onset
A patient with a severe bacterial infection is allergic to penicillin. Are monobactams a good treatment option?
Yes; aztreonam has no cross-sensitivity to penicillins/aminoglycosides and is usually nontoxic, making it a reasonable choice
What is the mechanism of action of griseofulvin?
Inhibition of microtubule function, thereby disrupting mitosis
A patient falls gravely ill with meningococcal meningitis. What do you give close contacts for prophylaxis?
Ceftriaxone, ciprofloxacin, or rifampin
A patient is given a triple antibiotic ointment for a superficial skin infection. Which antibiotic in the topical therapy is a cationic polypeptide?
Polymyxin B
Which antibiotic targeting bacterial protein synthesis can be given prophylactically before bowel surgery?
Neomycin (an aminoglycoside)
What is the mnemonic to remember for which protein synthesis inhibitors affect which bacterial ribosome subunits?
Buy AT 30, CCEL (sell) at 50: Aminoglycosides, Tetracyclines (30S); Chloramphenicol, Clindamycin, Erythromycin, Linezolid (50S)
A patient being treated for HIV is noted to have an ↑ creatine kinase level. What is the most likely cause?
An integrase inhibitor (eg, elvitegravir, dolutegravir)
What is the mechanism of action of caspofungin?
Inhibition of β-glucan synthesis, which disrupts cell wall synthesis
A child presents with discolored teeth, inhibited bone growth, and gastrointestinal distress secondary to antibiotic treatment. What is the antibiotic used?
A tetracycline, which should be avoided in children because of these adverse effects
Which carbapenem has limited Pseudomonas coverage?
Ertapenem
What are the common CNS adverse effects of fluoroquinolones?
Headaches, dizziness
What biochemical variation in MRSA makes nafcillin ineffective?
Alteration of the penicillin-binding protein target site
What is the mechanism of action of clindamycin?
It is a bacteriostatic antibiotic that inhibits peptide transfer (translocation) at the 50S ribosomal subunit
Which topical antifungal agent might you prescribe for vaginal candidiasis?
Topical nystatin
A patient who is HIV ⊕ and receiving antiretroviral therapy (ART) presents with heavy nosebleeds, bruising, hematuria and thrombocytopenia. What drug is the culprit?
Indinavir; this protease inhibitor causes thrombocytopenia, nephropathy and hematuria
What is the mechanism of action of daptomycin?
Creates transmembrane channels that disrupt cell membranes of gram ⊕ cocci
Describe the mechanism of action for sulfonamide antibiotics
They prevent folate synthesis by inhibiting dihydropteroate synthase, and in doing so, prevent bacterial replication (bacteriostatic)
What drug should not be taken with fluoroquinolones?
Antacids
What types of infections are the echinocandins used to treat?
Invasive aspergillosis, Candida infections
What is autoclaving?
An infection control technique that involves the use of pressurized steam at temperatures >120°C; this effect may be sporicidal
Acyclovir, famciclovir, and valacyclovir are guanosine analogs activated by viral thymidine kinase. What viral enzyme do they inhibit?
Viral DNA polymerase through chain termination
Which 2 azoles are commonly used to treat topical fungal infections?
Clotrimazole and miconazole
What are some adverse effects of penicillinase-resistant penicillins?
Hypersensitivity reaction and interstitial nephritis
Name the 2 drugs that belong to the rifamycin class of antibiotics.
Rifampin and rifabutin
Why is rifampin used with dapsone for the treatment of leprosy?
It delays the development of resistance to dapsone
Amphotericin B is used to treat which specific fungal infections?
Serious systemic mycoses such as Cryptococcus, Blastomyces, Coccidioides, Histoplasma, Candida, Mucor
A patient with an itchy scalp is found to have lice. Which anti-mite/louse agents may be used?
Treat PML (Pesty Mites and Lice) with PML (Permethrin, Malathion, Lindane) because they NAG you (Na, AChE, GABA blockade)
How does the microbial coverage of ampicillin compare to that of penicillin?
Ampicillin and amoxicillin have a broader spectrum of coverage (AMinoPenicillins are AMPed-up penicillin)
Why should clarithromycin be avoided in pregnant mothers with infections?
It is embryotoxic
What neurologic injury can sulfonamides cause in infants?
Kernicterus
What are the adverse effects of penicillin?
Hypersensitivity reactions, drug-induced interstitial nephritis, and direct Coombs ⊕ hemolytic anemia
What are the first-line antiviral agents used to treat herpes simplex virus infections?
Acyclovir, valacyclovir, famciclovir
A 16-year-old teenager with acne has a chlamydial infection. Why is your antibiotic of choice a tetracycline?
Tetracyclines treat both Chlamydia and acne
Name the peptidoglycan cross-linking, inhibiting antibiotics that are penicillinase resistant.
Oxacillin, naficillin, dicloxacillin
A patient on anidulafungin experiences skin flushing. What is the mechanism by which the drug causes this adverse effect?
Release of histamine
Penicillin is a D-Ala-D-Ala analog. What is its mechanism of action?
Binds transpeptidases (penicillin-binding proteins) and impairs cross-linking of peptidoglycan cell wall; also activates autolytic enzymes
What is the antiprotozoal agent of choice for leishmaniasis?
Sodium stibogluconate
A patient being treated for HIV is receiving a nucleoside reverse transcriptase inhibitor (NRTI) that does not require intracellular phosphorylation. What drug is this?
Tenofovir, which is already a nucleoTide; all other NRTIs require phosphorylation
A neonate has severe jaundice and no startle (Moro) reflex. Which antibiotic might his mother have taken during pregnancy?
A sulfonamide, which can cause kernicterus in the newborn
What is the effect of griseofulvin on the cytochrome P-450 system?
It is an inducer, resulting in ↑ cytochrome P-450 activity
Which azole should be used to prevent cryptococcal meningitis and Candida infections (any type) in patients with AIDS?
Fluconazole
What is the treatment for lepromatous leprosy?
Long-term regimen of dapsone, rifampin, and clofazimine
What is the mechanism of action of vancomycin?
It binds the D-Ala D-Ala part of cell wall precursors, thereby inhibiting the formation of peptidoglycan cell wall
What are 2 ways to reduce the toxicity of amphotericin B?
Use the liposomal formulation of the drug and hydrate to prevent nephrotoxicity
Drug Y is added to HIV-infected cells and this prevents transcription of HIV DNA by inhibiting HIV genome integration to the host cell. What category of drug was added?
An integrase inhibitor (dolutegravir, elvitegravir, raltegravir), which reversibly blocks viral DNA integration into host cell genome for transcription
A patient with COPD and a recent episode of pneumonia has ↑ serum levels of theophylline. Which antibiotic is he likely taking?
A macrolide
A patient with AIDS is started on dapsone for Pneumocystis jirovecii prophylaxis. Soon after, he develops a hemolytic crisis. Why?
Dapsone causes hemolysis in patients who are G6PD deficient
For which specific infections should the azole itraconazole be used to treat?
Blastomyces, Coccidioides, Histoplasma, or Sporothrix schenckii
What are the adverse effects associated with piperacillin and ticarcillin?
Hypersensitivity reactions
A pregnant woman being treated for HIV develops anemia. Which drug is responsible?
Zidovudine (ZDV)
How do bacteria develop resistance to penicillin?
By developing β-lactamases, such as penicillinase, which cleaves the β-lactam ring, or by direct mutations in the penicillin-binding proteins
Which infections is β-lactam ceftriaxone most effective against?
Meningitis, disseminated Lyme disease, gonorrhea
For which indications is cidofovir commonly used?
Cytomegalovirus retinitis in immunocompromised patients, acyclovir-resistant herpes simplex virus infections
How would an organism become resistant to linezolid?
From a point mutation in the ribosomal RNA
Name an antibiotic in the glycylcycline class.
Tigecycline
Are patients with penicillin allergies allergic to cephalosporins?
Cephalosporins have some cross-sensitivity with penicillins
What are the clinical uses of fluoroquinolones?
Treat gram ⊖ rods causing urinary and gastrointestinal tract infections (including Pseudomonas), some gram ⊕ organisms, and otitis externa
What is the mechanism of action of metronidazole for its antimicrobial effect?
Free radical-induced damage to DNA integrity
Name the agents that can be used to treat helminthic infections.
Pyrantel pamoate, Ivermectin, Mebendazole, Praziquantel, Diethylcarbamazine (helminths get PIMP’D)
Which bacterial species are targeted by ticarcillin and piperacillin?
Pseudomonas spp and gram ⊖ rods
A health care worker exposed to Mycobacterium tuberculosis is given the prophylactic drug, isoniazid. Which bacterial enzyme is needed for it to become active?
Catalase-peroxidase (encoded by KatG) converts isoniazid to its active form
Name 4 examples of second-generation cephalosporins.
Cefaclor, Cefoxitin, cefuroxime, and cefotetan (2nd graders wear fake fox fur to tea parties)
An man with HIV develops CMV esophagitis. He starts anti-CMV therapy. Soon after, he exhibits leukopenia, neutropenia, and thrombocytopenia. What likely caused the cytopenias?
He most likely began ganciclovir therapy for the CMV esophagitis and developed bone marrow suppression as an adverse effect
A man receives an antibiotic for vancomycin-resistant enterococcus. He notes tingling and decreased sensation in his hands. What is the antibiotic’s mechanism of action?
Binds to the 50S subunit and blocks formation of the initiation complex, inhibiting protein synthesis; this is neuropathy from linezolid
A patient taking antiretroviral therapy (ART) for HIV has nausea, diarrhea, lipodystrophy, and episodes of hyperglycemia. Which class of drug is she likely taking?
An HIV protease inhibitor
What is the adverse effect of cidofovir, and how can it be prevented?
Nephrotoxicity; coadministration with probenecid and IV saline solution
Which antifungal agent acts like amphotericin B but is only available in topical formulations because of systemic toxicity
Nystatin (same mechanism as amphotericin B)
Antibiotics that target bacterial ribosomes typically do so by targeting which 2 ribosomal components?
The 30S subunit and the 50S subunit
The big toe of a patient being treated for tuberculosis becomes red, swollen, and painful. Which antimycobacterial agent is the most likely cause?
Pyrazinamide, which can induce hyperuricemia
Which class of antibiotics should pregnant women avoid to prevent discoloration of teeth and abnormal bone growth in their children?
Tetracyclines
Which third-generation cephalosporin is effective against Pseudomonas infections?
Ceftazidime
Why are aminoglycosides ineffective against anaerobes?
They require oxygen for uptake
Which antibiotics should be avoided in pregnancy?
Sulfonamides, Aminoglycosides, Fluoroquinolones, Clarithromycin, Tetracyclines, Ribavirin, Griseofulvin, Chloramphenicol (SAFe Children Take Really Good Care)
You add a bacteriostatic antibiotic to bacteria and notice that the A-site tRNA binding is reduced. Which ribosomal subunit is inhibited?
30S (this is caused by tetracycline antibiotics)
Which organisms would you consider using linezolid against?
Gram ⊕ organisms, including MRSA and vancomycin-resistant enterococcus (VRE)
A patient with active tuberculosis is found to be HIV ⊕. How must his treatment regimen for either diagnosis be modified?
Rifampin causes potent CYP/UGT induction that ↓ protease inhibitor levels; it should be replaced with rifabutin
Use of aminoglycoside antibiotics is absolutely contraindicated in patients with what disorder?
Myasthenia gravis
What dermatologic adverse effect results from use of tetracyclines?
Photosensitivity
Name the carbapenem that is resistant to β-lactamase and is prescribed with cilastatin to prevent inactivation by the kidneys
Imipenem, a broad-spectrum antibiotic (“the kill is lastin’ with cilastatin”)
A patient with herpes simplex virus is believed to have a strain resistant to acyclovir. Which pyrophosphate analog should be considered?
Foscarnet
When would you consider using clindamycin over metronidazole to treat an anaerobic infection?
Clindamycin is useful for anaerobic infections above the diaphragm; metronidazole, for those below it
Name 3 antibiotics that belong to the tetracycline class of antibiotics.
Tetracycline, doxycycline, and minocycline
What is the mechanism of resistance to cephalosporins?
Via inactivation by cephalosporinases (a type of β-lactamase) or by structural changes in the penicillin-binding proteins (transpeptidases)
A patient is found to have drug-induced systemic lupus erythematosus (SLE) after completing prophylaxis for tuberculosis. Which drug is the most likely cause?
Isoniazid
Neuraminidase inhibitors are used to treat which viral infections?
Influenza A and B infections (neuraminidase inhibitors: eg, oseltamivir, zanamivir)
What is the binding site for foscarnet?
The pyrophosphate-binding site of either viral DNA/RNA polymerase or HIV reverse transcriptase (foscarnet = pyrofosphate analog)
What is the first-choice antiviral agent for an immunocompromised patient with cytomegalovirus retinitis?
Ganciclovir
A woman was given an antibiotic during pregnancy, and her baby has cartilage damage as a result. Which class of drug was it?
A fluoroquinolone
Name 5 antibiotics that belong to the aminoglycoside class of antibiotics.
Gentamicin, Neomycin, Amikacin, Tobramycin, Streptomycin; “Mean” (aminoglycosides) GNATS
What is the mechanism of action of ethambutol?
Ethambutol blocks arabinogalactan synthesis (via arabinosyl transferase inhibition) in the mycobacterial cell wall
Which antimycobacterial agents can be used for meningococcal prophylaxis?
Rifampin, rifabutin
A patient with tuberculosis is on a medication that blocks the 30S subunit of the bacterial ribosome. Identify the drug.
Streptomycin; this is typically a 2nd-line agent
Which adverse effects are associated with aminoglycosides?
Nephrotoxicity, Neuromuscular blockade, Ototoxicity, Teratogenicity; “mean” (aminoglycoside) GNATS caNNOT kill anaerobes
What is the mechanism of action of tigecycline?
Like all glycylcyclines, it binds the 30S ribosome to inhibit bacterial protein synthesis; it is bacteriostatic
Which generation of cephalosporins work particularly well for meningitis, and why?
Third generation because they can cross the blood-brain barrier
What infectious processes are commonly treated using clindamycin?
Aspiration pneumonia, lung abscesses, and oral infections involving anaerobic organisms
A 65-year-old man says that ciprofloxacin worked well for previous bouts of traveler’s diarrhea. Why should another class be used this time?
Fluoroquinolones may cause tendinitis/tendon rupture in people older than 60 years of age (Fluoroquinolones hurt attachments to your bones)
Aztreonam is an example of what subclass of β-lactam drugs?
Monobactams
Name 3 classes of antibiotics that work by binding to the bacterial 30S ribosomal subunit.
Aminoglycosides (eg, gentamicin), glycylcycline (eg, tigecycline), and tetracyclines (eg, doxycycline)
Which 2 systemic reactions accompanied by diffuse rash can be seen with vancomycin toxicity?
Red man syndrome (diffuse flushing) and DRESS (drug reaction with eosinophilia and systemic symptoms) syndrome
Ceftaroline, a fifth-generation cephalosporin, is active against which organisms?
Gram ⊕ and gram ⊖, including MRSA (note that it has no coverage against Pseudomonas infections)
What are the adverse effects of chloroquine?
Retinopathy and pruritus (particularly in dark-skinned patients)
What are the major adverse effects associated with isoniazid?
Neurotoxicity and hepatotoxicity (INH: Injures Neurons and Hepatocytes), can also lower the seizure threshold
Your patient being treated for tuberculosis experiences paresthesias in her arms and legs. How could you have prevented this adverse effect?
By coadministering pyridoxine (vitamin B6) to prevent neurotoxicity induced by isoniazid
A 20-year-old woman presents with dysuria and frequency. Urinalysis is positive for nitrites and leukocyte esterase. Most common treatment?
Trimethoprim-sulfamethoxazole (TMP-SMX) for simple urinary tract infections
Which of the guanosine-analog antiviral drugs is more toxic to host enzymes?
Ganciclovir (compared to acyclovir)
Name 3 echinocandins.
Anidulafungin, caspofungin, and micafungin
Which macrolide antibiotics inhibit cytochrome P450 enzymes?
Erythromycin, clarithromycin
Which azole antifungal is best for treating Aspergillus and Candida infections?
Voriconazole
Vancomycin is bactericidal, with what exception?
Clostridium difficile (it is bacteriostatic against it)
A 40-year-old man with MRSA cellulitis is treated for a week with an antibiotic and notices reduced hearing in both ears. What drug was he given?
Vancomycin, which is associated with ototoxicity
What is the consequence of treating latent tuberculosis solely with rifampin?
Development of Rapid resistance when Rifampin is used alone
Compared to other commonly used antiviral agents, what is the half-life of cidofovir?
It has a long half-life
Describe the mechanism of action of trimethoprim.
It blocks dihydrofolate reductase (like pyrimethamine), thus preventing bacterial replication (bacteriostatic)
List 2 infection control agents that are not sporicidal and work by denaturing proteins and disrupting cell membranes.
Alcohols and chlorhexidine
What is the mechanism of action of pyrazinamide?
Unknown, but it works best at acidic pH (allowing it to work in host phagolysosomes) and is converted to its active form, pyrazinoic acid
A pregnant woman is ⊕ for a group B streptococcal infection. What antibiotic should she receive to prevent complications in the newborn?
Intrapartum penicillin G or ampicillin
A young woman presents for treatment of tinea corporis. What do you need to remember when considering the antifungal griseofulvin for her?
It is teratogenic and contraindicated in pregnancy; perform a pregnancy test before starting therapy
A patient has a deep tissue vanco-resistant enterococci infection. What antibiotic do you prescribe?
Tigecycline
Why is chloroquine a poor treatment for Plasmodium falciparum malaria?
Because the resistance rate is too high
What is the mechanism of action of abacavir?
A nucleoside reverse transcriptase inhibitor (NRTI); abacavir inhibits nucleotide binding to reverse transcriptase; NRTIs lack a 3′ OH group; this stops DNA synthesis
Pancytopenia develops in a patient being treated for HIV. Which drugs should be considered to counteract this adverse effect?
Granulocyte colony-stimulating factor (G-CSF) and erythropoietin (EPO) to combat bone marrow suppression
What is the mechanism of action of quaternary amines?
Impairment of cell membrane permeability; the effect is not sporicidal
What is the mechanism of action of isoniazid?
Isoniazid targets mycolic acid synthesis in the mycobacterial cell wall
A 39-year-old man has an acid-fast bacillus infection. After starting therapy, he can no longer see red-green colors. What is the mechanism of action of the offending agent?
Inhibition of arabinosyltransferase prevents carbohydrate polymerization within Mycobacterium tuberculosis cell walls; red-green color blindness indicates ethambutol toxicity
What is the mechanism of action of polymyxin antibiotics?
Cause membrane damage, leakage of cell contents, and cell death by binding to the phospholipids in the membranes of gram ⊖ bacteria
What are the adverse effects of foscarnet therapy?
Electrolyte abnormalities (hypo- or hypercalcemia, hypo- or hyperphosphatemia, hypomagnesemia, or hypokalemia), seizures, nephrotoxicity
What is the mechanism by which bacteria develop resistance to chloramphenicol?
By acquiring a plasmid-encoded acetyltransferase that inactivates the drug
A man with cytomegalovirus is taking a drug that causes viral DNA chain termination. What modifications must occur to activate the drug?
Formation of 5′-monophosphate by CMV kinase and a triphosphate by cellular kinases
What are the major adverse effects of dapsone?
Hemolysis in patients with G6PD deficiency, methemoglobinemia, and agranulocytosis
What is the mechanism of action of mebendazole?
Inhibition of microtubules
A man presents with both mucocutaneous and genital herpes simplex virus lesions. Which antiviral agents may be considered?
Acyclovir, valacyclovir, famciclovir
A patient is started on a drug for influenza with the goal of shortening the duration of symptoms. What is the mechanism of action of the drug?
Inhibition of viral neuraminidase, which blocks the release of viral progeny (the drug is oseltamivir or zanamivir)
A strain of tuberculosis is resistant to treatment with isoniazid. What is the mechanism of resistance?
Mutations that lead to the underexpression of KatG
A 70-year-old man on warfarin is started on a sulfonamide for an infection. He soon notes easy bruising and dark tarry stools. What happened?
Sulfonamides increase plasma concentration of warfarin (and other drugs) by displacing it from albumin
A patient being treated for HIV experiences paresthesia and ↓ sensation in both legs. What is the most likely cause?
Nucleoside reverse transcriptase inhibitor- (NRTI) induced peripheral neuropathy
A patient being treated with clindamycin for pneumonia develops fever and loose stools. What is the bacterial culprit?
Clostridium difficile overgrowth in the colon
A patient has a Pediculus and Pthirus infection. Which anti-mite/louse agents can be used?
Treat PML (Pesty Mites and Lice) with PML (Permethrin, Malathion, Lindane) because they NAG you (Na, AChE, GABA blockade)
What is the recommended combination of antiretroviral therapy (ART) classes in HIV therapy?
2 nucleoside reverse transcriptase inhibitors (NRTIs) and a third agent (integrase inhibitors are preferred)
Why are fluoroquinolones contraindicated in women who are pregnant or nursing and patients younger than 18 years of age?
Possibility of cartilage damage (fluoroquinolones hurt attachments to your bones)
A patient requests prophylaxis against Mycobacterium tuberculosis before travel. What is the one drug that can be used as solo prophylaxis?
Isoniazid
What is the mechanism of action of ribavirin?
Competitive inhibition of inosine monophosphate dehydrogenase, thereby inhibiting synthesis of guanine nucleotides
Which drug is flucytosine frequently paired with to treat systemic fungal infections?
Amphotericin B (especially in cases of cryptococcal meningitis)
How many generations of cephalosporins antibiotics are there?
5 generations
What is the mechanism of hydrogen peroxide in disinfection and sterilization?
Induction of free radical oxidation; the effect is sporocidal
What is the mechanism of action of elvitegravir?
As an integrase inhibitor, elvitegravir stops HIV genome integration into host cell DNA
What antibiotic is used as prophylaxis against postsurgical Staphylococcus aureus infection?
Cefazolin
A certain antibiotic inhibits bacterial translocation and the ribosomal activity is measured. Would 30S activity be decreased?
No, antibiotics that act on translocation all inhibit the 50S subunit (eg, macrolides, clindamycin)
What organisms are targeted by clindamycin?
Organisms causing anaerobic lung infections (eg, Clostridium perfringens, Bacteroides spp) and organisms causing group A streptococcal infections
Which protein synthesis-inhibiting antibiotics are bactericidal?
Aminoglycosides (note that linezolid is variable: bacteriostatic and bactericidal)
A patient taking an oxazolidinone for MRSA complains of headache and rapid heart rate. On exam he is shivering. Other adverse effects of this drug?
Peripheral neuropathy, bone marrow suppression (especially thrombocytopenia) from linezolid toxicity, serotonin syndrome
A patient being treated for tuberculosis presents with fatigue and a low hemoglobin level. The blood smear shows ringed sideroblasts. What is the most likely cause?
Isoniazid-induced pyridoxine (vitamin B6) deficiency; diagnosis: sideroblastic anemia
A patient with HIV is found to have a CD4+ count <50 cells/mm3. Aside from trimethoprim-sulfamethoxazole (TMP-SMX), what other prophylactic therapy should be started?
Azithromycin or clarithromycin for Mycobacterium avium complex
Fungi treated with a certain antifungal agent have ↑ amounts of intracellular lanosterol. Which cellular structure is likely compromised?
The cell membrane (due to azoles inhibiting intracellular 14-α-demethylase, which reduces ergosterol synthesis)
Name the antibiotic that belongs to the oxazolidinone class.
Linezolid
Trimethoprim-sulfamethoxazole is used to treat which pulmonary infection in patients who are HIV ⊕?
Pneumocystis jirovecii pneumonia
A woman has a herpes simplex virus infection that does not respond to acyclovir. What drug should you try next?
Cidofovir or foscarnet, viral DNA polymerase inhibitors that are useful for acyclovir-resistant HSV
A patient with HIV has a CD4+ count of 150 cells/mm3. Prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMX) is started. What infection is the patient being protected against?
Pneumocystis pneumonia (if CD4+ count is <200 cells/mm3)
What is the mechanism of action of tetracyclines?
They are bacteriostatic, binding to 30S and preventing the attachment of aminoacyl-tRNA
What are the most common uses for chloramphenicol?
Treatment of meningitis (Haemophilus influenzae, Neisseria meningitidis, Streptococcus pneumoniae) and rickettsial diseases (eg, Rocky Mountain spotted fever)
What is the mechanism of action of praziquantel?
↑ Ca2+ permeability and vacuolization
Which organisms do second-generation cephalosporins cover?
Gram ⊕ cocci, Haemophilus influenzae, Enterobacter aerogenes, Neisseria spp, Serratia marcescens, Proteus mirabilis, Escherichia coli, Klebsiella (HENS PEcK)
A woman has recurrent dysuria, urgency, and frequency. What do you prescribe as prophylaxis against future infections?
Trimethoprim-sulfamethoxazole (TMP-SMX) is given for recurrent UTIs
Name 4 drugs that can be given with penicillin antibiotics to prevent degradation of the antibiotics by β-lactamase (penicillinase).
β-lactamase inhibitors: Clavulanic acid, Avibactam, Sulbactam, Tazobactam (CAST)
Tetracyclines are used to treat infections with which 2 organisms that are transmitted by ticks?
Borrelia burgdorferi and Rickettsia
What is a common suffix for drugs of the protease inhibitor class used to treat HIV?
-navir: atazanavir, darunavir, fosamprenavir, indinavir, lopinavir, ritonavir, saquinavir
Which antibiotic is most commonly used preoperatively to protect against Staphylococcus aureus wound infections?
Cefazolin
Name the drugs that belong to the sulfonamide class.
Sulfamethoxazole (SMX), sulfadiazine, sulfisoxazole
Name the narrow spectrum, penicillinase resistant antibiotics.
Dicloxacillin, nafcillin, oxacillin
Why are tetracyclines contraindicated in pregnancy?
Because they inhibit bone growth in children
What is the mechanism of action of metronidazole?
Forms free radical metabolites that damage bacterial DNA, leading to cell death (bactericidal)
Which organisms are typically not covered by the first 4 generations of cephalosporins?
LAME: Listeria, Atypicals (Chlamydia, Mycoplasma), MRSA, Enterococci
What is the mechanism of resistance of Plasmodium falciparum to chloroquine?
Membrane pumps ↓ intracellular concentrations of the drug
Why do antibiotics that inhibit protein synthesis generally not affect human cells?
They target bacterial ribosome 70S, which is smaller than the 80S of humans; thus human ribosomes are left unaffected
What drug is used for Mycobacterium tuberculosis prophylaxis?
Isoniazid
A patient being treated for HIV exhibits a rash and ↑ values on liver function tests. What is the most likely cause?
A non-nucleoside reverse transcriptase inhibitor (NNRTI); a rash and hepatotoxicity are common adverse effects of all NNRTIs
Anion gap metabolic acidosis develops in a patient being treated for HIV. What is the most likely cause?
Nucleoside reverse transcriptase inhibitor- (NRTI) induced lactic acidosis (nucleoside agents only)
What drug regimen can you use to treat a Mycobacterium avium-intracellulare infection?
Azithromycin or clarithromycin plus ethambutol; rifabutin or ciprofloxacin can be added
Name the penicillins that are effective against Pseudomonas spp.
Piperacillin and ticarcillin
Why should ribavirin be used with caution in young women?
It is teratogenic
You add amphotericin B to a fungal culture and note an ↑ in the electrolyte content of the culture media. Explain the mechanism.
Amphotericin B binds ergosterol (unique to fungi) and forms membrane pores (“tears” holes), allowing leakage of electrolytes
A man receives acyclovir for a viral infection that is later found to be cytomegalovirus. How does the management change?
Acyclovir is not effective against CMV, so ganciclovir or a viral DNA polymerase inhibitor (eg, foscarnet, cidofovir) should be used instead
A patient who is HIV ⊕ contracts tuberculosis. Why is rifabutin favored over rifampin in this case?
Less P-450 stimulation (Rifampin ramps up cytochrome P-450, but rifabutin does not)
What is the mechanism of action of acyclovir?
It is a guanosine analog that inhibits DNA replication
An antifungal agent interferes with mitotic spindles. Which conditions is this drug used for?
Superficial infections (oral therapy) and dermatophytoses; the drug is griseofulvin
An immunocompromised man has cytomegalovirus retinitis that does not respond to ganciclovir. Which antiviral agent should be considered?
Foscarnet
Which of the 2 aminopenicillins has a greater oral bioavailability?
Amoxicillin (AmOxicillin has better Oral bioavailability)
What is the mechanism of action of the antipseudomonal penicillins?
Same as that of penicillin (they inhibit peptidoglycan cross-linking in bacterial cell walls)
Name 2 viral DNA polymerase inhibitors and the 2 viruses they are commonly used to treat.
Cidofovir and foscarnet (for herpes simplex virus and cytomegalovirus)
A patient treated for onychomycosis complains of gastrointestinal upset, headache, and taste disturbance; liver function test results are abnormal. Most likely cause?
Terbinafine toxicity
A patient being treated for tuberculosis experiences tinnitus, vertigo, ataxia, and nephrotoxicity. Which antimycobacterial agent is the most likely cause?
Streptomycin
A patient with COPD being treated with inhaled steroids has oral candidiasis (thrush). What medication do you prescribe?
Nystatin (swish and swallow)
What is the major toxicity associated with ethambutol?
Potentially reversible optic neuropathy, commonly manifesting as red-green color blindness; think “eyethambutol”
Which protein synthesis-inhibiting antibiotics are bacteriostatic?
Tetracyclines, chloramphenicol, clindamycin, erythromycin (linezolid is variable: bacteriostatic and bactericidal)
A patient is on voriconazole for a serious Aspergillus infection, but the infection worsened. What azole should be used next?
Isavuconazole
Which antibiotics can be used to treat vancomycin-resistant enterococci (VRE)?
Linezolid, streptogramins (quinupristin, dalfopristin), and tigecycline
What is the mechanism of action of dicloxacillin, nafcillin, and oxacillin?
Inhibit peptidoglycan cross-linking in bacteria cell walls (same as penicillin)
What is the treatment for tuberculoid leprosy?
Long-term regimen of dapsone and rifampin
A man with HIV finds that taking his HIV protease inhibitor makes some other medications more potent. Inhibition of which enzyme is to blame?
Cytochrome P-450, which is inhibited by ritonavir
Fourth-generation cephalosporins have ↑ activity against which organisms?
Pseudomonas and gram ⊕ organisms
Name the fourth-generation cephalosporin.
Cefepime
Carbapenems are used to treat infections with which type of organisms?
Gram ⊕ cocci, gram ⊖ rods, and anaerobes (wide spectrum)
What are the adverse effects of therapy with amphotericin B?
Think “amphoterrible” B: fevers/chills (“shake and bake”), nephrotoxicity, hypotension, anemia, arrhythmias, IV phlebitis
Which agent, when given with amoxicillin, protects against β-lactamases?
Clavulanic acid
What drug prevents HIV virions from attaching to host cells?
Maraviroc
An HIV drug inhibits reverse transcriptase. What 2 classes of HIV drugs utilize this mechanism of action?
Nucleoside reverse transcriptase inhibitors (NRTIs) and non-nucleoside reverse transcriptase inhibitors (NNRTIs)
Name the penicillins that are sensitive to penicillinase.
Penicillin and the aminopenicillin family (amoxicillin and ampicillin)
Name 2 antipseudomonal antibiotics that interfere with peptidoglycan cross-linking.
Ticarcillin, piperacillin
What are the current guidelines for initiation of antiretroviral therapy (ART)?
ART is commonly started at diagnosis of HIV; high viral load or presence of AIDS-defining illness is a stronger indication for starting treatment
What is the 4-drug therapy commonly used to treat tuberculosis?
Rifampin, Isoniazid, Pyrazinamide, and Ethambutol (RIPE for treatment)
A patient with HIV is on a medication that binds to gp41 protein. Which class of HIV medication does this drug belong to?
Fusion inhibitors, which prevent viral entry; this is enfuvirtide
What organisms does tigecycline cover?
Broad-spectrum anaerobic gram ⊖ and gram ⊕ organisms, multidrug-resistant organisms (MRSA, VRE); also deep tissue infections
Renal failure is found in a patient being treated for cytomegalovirus retinitis who presented with multiple seizures. What is the most likely cause of the renal failure?
Foscarnet-induced nephrotoxicity (foscarnet can also induce seizures)
What is the mechanism of action of ledipasvir and ombitasvir?
NS5A inhibition, preventing RNA replication
What is the function of the HIV-1 protease from the pol gene?
Cleaving the polypeptides made from the HIV mRNA into functional components
What is the antiprotozoal agent of choice for a Trypanosoma cruzi infection?
Nifurtimox
A patient being treated for HIV has upper abdominal pain radiating to the back and Grey Turner sign. What’s the most likely cause?
Didanosine-induced pancreatitis
A patient with HIV has a CD4+ count <100 cells/mm3. Prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMX) is started. What infection is the patient being protected against?
Pneumocystis pneumonia (if CD4+ count is <200 cells/mm3) and toxoplasmosis (if CD4+ count is <100 cells/mm3)
What is the mechanism by which mycobacteria develop resistance to rifamycin, particularly with monotherapy?
Mutations ↓ the drug’s ability to bind to the RNA polymerase
How do fluoroquinolones and quinolones exert their antibacterial effects?
DNA gyrase inhibition
Name 2 examples of first-generation cephalosporins.
Cefazolin and cephalexin
Name some specific bugs that penicillin is particularly effective against.
Streptococcus pneumoniae, Streptococcus pyogenes, Actinomyces, Neisseria meningitidis, Treponema pallidum
Which disinfection and sterilization techniques are not sporicidal?
Alcohols, chlorhexadine, quaternary amines
Compared to that of other β-lactams, cephalosporins are more resistant to what enzyme?
Penicillinase
Why should griseofulvin be used with caution in young women?
It is teratogenic
Penicillin is the prototype for which class of antibiotics?
β-lactams
What is the mechanism of action of chlorine against spores?
Oxidation and denaturation of proteins; the effect is sporicidal
A patient with methicillin-resistant Staphylococcus aureus is given an antibiotic that has decreased absorption when taken with milk. Which antibiotic class does this drug belong to?
Tetracyclines; this is doxycycline
Name 5 uses for tetracyclines.
Treat Mycoplasma pneumoniae, Chlamydia, Borrelia burgdorferi, and Rickettsia infections, and acne
A patient with an inherited mutation causing ↑ dehydropeptidase I activity is given meropenem to treat septicemia. How does this affect seizure risk?
Meropenem is resistant to dehydropeptidase I activity, so its plasma levels will not ↑; therefore, no change to the risk of seizures
Aztreonam inhibits peptidoglycan cross-linking by binding to which substance?
Penicillin-binding protein 3
What are the musculoskeletal adverse effects of fluoroquinolones
Leg cramps, myalgia, tendonitis and tendon rupture (in those over 60 years of age or who are taking prednisone), and damage to cartilage in children
An unvaccinated child contracts Haemophilus influenzae type b. Which antimycobacterial agents may be used as prophylaxis for the child’s contacts?
Rifampin, rifabutin
What is the mechanism of action of lindane?
Blockage of GABA channels, thereby causing neurotoxicity
What is the antiprotozoal agent of choice for toxoplasmosis?
Pyrimethamine
Which drugs can you prescribe to a patient with Plasmodium falciparum malaria?
Artemether/lumefantrine or atovaquone/proguanil
What agents is autoclaving not reliably successful against?
Prions
You want to prescribe a triple therapy regimen for a patient with Helicobacter pylori, but she has a penicillin allergy. How do you alter your treatment plan?
Replace amoxicillin with metronidazole (triple therapy also includes a proton pump inhibitor and clarithromycin)
An infant has a diaper rash that you determine is a fungal infection. You prescribe a topical medication. What is its mechanism of action?
It forms membrane pores on fungi, allowing electrolytes to leak; the drug is nystatin
Why are tetracycline antibiotics not a good choice for infections of the central nervous system (CNS)?
They have limited CNS penetration
A man with a systemic cryptococcal infection develops meningitis. How must you change the regimen of amphotericin B?
Consider intrathecal administration and co-administering with flucytosine
Which antibiotics belong to the carbapenem group?
Doripenem, ertapenem, imipenem, meropenem
Name 4 examples of third-generation cephalosporins.
Ceftriaxone, cefotaxime, ceftazidime, cefpodoxime
What is the mechanism of action of flucytosine?
Flucytosine is converted to 5-fluorouracil by cytosine deaminase; 5-fluorouracil inhibits DNA and RNA synthesis
What medications can be given to travelers for malaria prophylaxis?
Atovaquone-proguanil, mefloquine, doxycycline, primaquine, or chloroquine (for areas with sensitive species)
A patient with strep throat is allergic to penicillin. Which part of protein synthesis is inhibited by the antibiotic that he receives instead?
Translocation; he was likely given a macrolide antibiotic; think macroslides
A patient takes trimethoprim-sulfamethoxazole (TMP-SMX) and you later observe megaloblasts on a blood smear. How could this have been prevented?
By coadministration of leucovorin (folinic acid); TMP-SMX can cause megaloblastic anemia, leukopenia, granulocytopenia, and hyperkalemia (TMP Treats Marrow Poorly)
Sulfonamides are active against which organisms?
Gram ⊕ and gram ⊖ organisms, Nocardia
Trimethoprim and sulfamethoxazole are used in combination to treat which types of infections?
Urinary tract infections, toxoplasmosis prophylaxis, Shigella, Salmonella, and Pneumocystis jirovecii pneumonia treatment and prophylaxis
Adding a guanine nucleotide synthesis blocker to virus-infected cells blocks virion assembly. What 2 viruses may be infecting these cells?
Respiratory syncytial virus or hepatitis C virus (the drug is likely ribavirin)
How does griseofulvin influence cancer risk?
It is carcinogenic, so cancer risk is ↑
What are the adverse effects of the NS3/4A inhibitors grazoprevir and simeprevir?
Grazoprevir causes photosensitivity and rash; simeprevir causes headache and fatigue
How do viruses develop resistance to ganciclovir?
By a mutated viral kinase
Name 2 antibiotics that work by blocking peptidoglycan synthesis.
Bacitracin and vancomycin (glycopeptides)
How do iodine and iodophors work to control infection?
Halogenation of proteins, RNA, and DNA; may be sporicidal
Monobactams are particularly useful in which patient populations infected with gram ⊖ rods?
In patients with penicillin allergy or patients with renal insufficiency in whom aminoglycosides should be avoided
Against which classes of bacteria do penicillins exhibit bactericidal activity?
Gram ⊕ cocci, gram ⊖ cocci, gram ⊕ rods, spirochetes
What are the adverse effects of the NS5B inhibitors sofosbuvir and dasabuvir?
Fatigue, headache
A patient who recently started an antibiotic for tuberculosis has orange-colored urine and sweat. What is the drug’s mechanism of action?
Inhibition of DNA-dependent RNA polymerase; this is Rifamycin, RNA polymerase inhibitor
List the organisms that can be treated with metronidazole.
Giardia, Entamoeba, Trichomonas, Gardnerella vaginalis, Anaerobes (Bacteroides, Clostridium difficile), Helicobacter pylori (GET GAP on the Metro with metronidazole!)
What prophylaxis do you give for streptococcal pharyngitis in a boy with a history of rheumatic fever?
Oral penicillin V or benzathine penicillin G
β-lactamase inhibitors are used to protect antibiotics from bacterial penicillinases. Would you use these with vancomycin?
No, because vancomycin is resistant to β-lactamases
Ethambutol is used to treat which bacterial infection?
Mycobacterium tuberculosis
Against which organisms are dicloxacillin, nafcillin, and oxacillin useful?
Staphylococcus aureus (use naf [nafcillin] for staph)
Name 3 non-nucleoside reverse transcriptase inhibitors (NNRTIs) used to treat HIV.
Delavirdine, efavirenz, nevirapine
A patient currently on erythromycin is found to have an electrical cardiac abnormality on EKG. What is it most likely to be?
Prolonged QT interval
A drug added to HIV-infected cells stops viral particle budding and release. HIV proteins remain w/in cells. Which drug class was added?
A protease inhibitor (eg, atazanavir), which blocks proteolytic processing
Name 3 examples of macrolide antibiotics.
Erythromycin, azithromycin, and clarithromycin
Apart from tuberculosis, which other mycobacterial infection is rifampin used for?
Mycobacterium leprae (it delays resistance to dapsone)
What are the 5 adverse effects caused by macrolides?
MACRO: GI Motility issues, Arrhythmia (prolonged QT), acute Cholestatic hepatitis, Rash, eOsinophilia
What are some of the conditions for which daptomycin is used?
Vancomycin-resistant enterococcus, bacteremia, endocarditis, and skin infections with Staphylococcus aureus (especially MRSA)
What antibiotics could you prescribe for a patient who is HIV+ with a CD4+ count of 10 to protect against Mycobacterium avium-intracellulare infection?
Azithromycin or rifabutin
What disease is dapsone used to treat, and what disease is it used for prophylaxis?
Treatment: leprosy (for both lepromatous and tuberculoid forms); prophylaxis: Pneumocystis jirovecii (treatment if used with trimethoprim)
What alkylating agent can be used for sterilization?
Ethylene oxide
