Antimicrobials I Flashcards
One good principle to keep in mind, when prescribing antibiotics, is that bacteriostatic drugs are only effective in ______________ patients.
immunocompetent
Think about it: if someone is neutropenic or otherwise immunologically impaired, then the static population of bacteria would still be able to live and produce toxins.
What is PAE?
Post-antibiotic effect: a period in which the drug is below its MIC yet the bacteria do not grow
Interestingly, all of the broad-spectrum antibiotics –chloramphenicol, sulfonamides, tetracycline, and trimethoprim –are ________________.
bacteriostatic
What two properties make cell-wall synthesizers have high selective toxicity?
(1) Only bacteria have cell walls, so the proteins targeted by cell-wall synthesis inhibitors do not inhibit human proteins.
(2) Cell-wall synthesis occurs outside the cell, so cell-wall synthesis inhibitors don’t need to penetrate cell membranes.
What is the incidence of type I hypersensitivity reactions to penicillin?
1 : 10,000 (of which about 10% will die)
Which penicillin can be given orally?
Penicillin V (think of how penicillin G is associated with the IVy around Princess Ellen’s neck –the vine that is grabbing her from behind)
Which beta-lactam has a neutralizing amino group?
The amino-group beta-lactams have “am-“ in their names: amoxicillin and ampicillin. This allows them to pass through the outer cell membrane.
Although the second-generation cephalosporins are not commonly used, what bacteria can they kill that the first-generation cephalosporins cannot?
HeNS: Haemophilus influenzae, Neisseria, and Serratia
Remember General Fox’s teapot with hens on it.
Quickly recap the ribosomal spots targeted by different antibiotics.
30S: aminoglycosides, tetracyclines
50S: clindamycin, chloramphenicol
50S – 23S subunit: macrolides
Which of the ribosome-targeting antibiotics is bacteriocidal? And why?
Aminoglycosides are bacteriocidal because they cause misreading of mRNA and subsequent accumulation of garbled protein.
Aminoglycosides are only effective against _____________.
aerobic, Gram-negative bacteria
Use of which antibiotic can cause fungal superinfections?
Tetracyclines
You might use tetracyclines to treat _________________.
Chlamydia, Mycoplasma, Rickettsia, Brucella, Borrelia burgdorferi, and spirochetes
Again, what is Dr. French’s mnemonic for the hepatically metabolized antibiotics?
DQ CRIMES: Doxycycline fluoroQuinolones Clindamycin, Chloramphenicol Rifampin Isoniazide Metronidazole Erythromycin Sulfonamides
Why is sulfamethoxazole-trimethoprim not toxic to human cells?
Because bacteria need to make their own folate, while humans take it in from the environment
What is unique about the metabolism of sulfonamides?
It is metabolized to a less-soluble form. This can aggravate renal crystalluria.
Which enzyme is inhibited by the antibiotic that can form crystals in the renal tubule?
Dihydropteroate synthase (being sulfonamides)
Trimethoprim inhibits ______________.
dihydrofolate reductase
What is the teratogenic mechanism of sulfamethoxazole-trimethoprim?
It displaces bilirubin from albumin and can cause kernicterus.
Fluoroquinolones inhibit ______________.
DNA gyrase and topoisomerase IV –both involved in the uncoiling of DNA
True or false: fluoroquinolones are highly toxic because they inhibit human DNA gyrase.
False. Humans don’t have gyrase.
What can decrease the absorption of fluoroquinolones?
Metal cations (e.g., antacids, iron, milk)
What two drug interactions are common in use of fluoroquinolones?
(1) Concomitant use of NSAIDs increases risk of seizure
(2) Fluoroquinolones inhibit metabolism of theophylline
Metronidazole causes a shift to _______________.
lactate metabolism
The mechanism of _______________ is similar to that of metronidazole.
nitrofurantoin
Use of nitrofurantoin for UTIs is increasing due to increasing resistance to _____________.
sulfamethoxazole-trimethoprim
What adverse effect can fluoroquinolones cause in children younger than 12?
Impaired cartilage development
What is the most common use of polymyxin?
Pseudomonal meningitis
How can you enhance the excretion of Bactrim?
By raising the pH of the urine
How are penicillins excreted?
Renally (hence the interstitial nephritis that can result from penicillin use)
True or false: penicillins are competitive inhibitors of transpeptidases.
False. They covalently bind and thus irreversibly inhibit PBPs.
Which antibiotic concentrates in the lungs?
Macrolides
Which antibiotic can cause cholestatic hepatitis?
Macrolides
How does nitrofurantoin work?
It is a DNA-damaging agent.
Nitrofurantoin is mainly used for ________________.
Gram-negative UTIs
Sulfamethoxazole inhibits a reaction that has what starting reactants?
Para-amino benzoic acid (PABA) and pteridine
By what ways do bacteria become resistant to sulfonamides?
- Increased production of PABA
- Modified dihydropteroate synthase
- Decreased permeability to sulfonamides
- Obtaining folate and other end products from pus
Which antibiotic is metabolized by acetylation?
Bactrim
Sulfasalazine is converted to _________________ in the gut, accounting for its benefit in those with ulcerative colitis.
5-ASA
Topical Bactrim is frequently used to prevent what infection in burn patients?
Pseudomonas aeruginosa
Fluoroquinolones are most effective against ___________ bacteria, though they can also kill _____________.
Gram-negative; Gram-positive
Bacteria resistant to ___________________ are usually still susceptible to fluoroquinolones.
aminoglycosides and beta-lactams
How do bacteria typically become resistant to fluoroquinolones?
Efflux pumps
There is one fluoroquinolone that is not renally cleared and will thus not treat UTIs: _____________.
moxifloxacin
The most common use of fluoroquinolones is ________________.
UTIs in the elderly
Which antibiotics affect tRNA binding?
Tetracycline
Bactrim can cause agranulocytosis, aplastic anemia, crystalluria, and _____________.
photosensitivity
Which antibiotic can treat prostatitis?
Fluoroquinolones
Metronidazole resistance can occur when bacteria _______________.
shift from acetate to lactate
