kaplan review Q partial 1 topics Flashcards
- A patient suffering from invasive aspergillosis is first administered NSAIDs,
antihistamines, and adrenal glucocorticoids prior to administration of an
antifungal drug. The antifungal drug works by
A. binding to tubulin
B. inhibiting squalene epoxidase
C. inhibiting thymine synthesis
D. binding to ergosterol
E. inhibiting 14α-demethylase
Answer: D. Life-threatening invasive aspergillosis, with necrotizing pneumonia, most commonly occurs in severely immunocompromised patients. The
mortality rate approaches 50%, but high intravenous doses of amphotericin
B may be lifesaving. Intravenous amphotericin B causes infusion-related
hypotension (via histamine release), fever, and chills, which may be attenuated by the prior administration of NSAIDs and antihistamines. Adrenal
steroids may provide supplementary stress support. Amphotericin B binds
to ergosterol in fungal membranes, opening pores and disrupting membrane
permeability.
A patient is prescribed isoniazid prophylactically since another family member currently has tuberculosis. When the patient ends up getting tuberculosis
despite prophylaxis, resistance to isoniazid is suspected. In what way did this
resistance likely develop?
A. Decreased intracellular accumulation of the drug
B. Inactivation of the drug via N-acetyltransferases
C. Increased synthesis of mycolic acids
D. Mutations in the gene coding for DNA-dependent RNA polymerase
E. Reduced expression of the gene that encodes a catalase
. Answer: E. For antitubercular activity, isoniazid (INH) must first be metabolically activated via a catalase present in mycobacteria. A decrease in
expression of the cat G gene that encodes this enzyme is the mechanism of
high-level resistance to INH
A 7-year-old child presents with pharyngitis and fever of 2 days’ duration,
and microbiology reveals small, translucent, beta-hemolytic colonies sensitive in vitro to bacitracin. Past history includes a severe allergic reaction to
amoxicillin when used for an ear infection. The physician needs to treat this
infection, but prefers not to use a drug that needs parenteral administration.
Which one of the following agents is most likely to be appropriate in terms
of both effectiveness and safety?
A. Azithromycin
B. Cefaclor
C. Doxycycline
D. Penicillin G
E. Vancomycin
Answer: A. Azithromycin is highly effective as an oral agent in the management of pharyngitis caused by gram-positive cocci and may necessitate only
a short course of therapy. In patients who have marked hypersensitivity to
penicillins, it is inappropriate to use a cephalosporin, even though cefaclor
is active against common oropharyngeal pathogens. Doxycycline should
not be used in children. One must assume that complete cross-allergenicity
exists between different members of the penicillin class of antibiotics, and,
in any case, penicillin G is not usually given orally because of its lability in
gastric acid. Vancomycin would need parenteral administration, and this
antibiotic should be reserved for more serious bacterial infections.
. A woman has a sexually transmitted disease, and the decision is made to treat
her with antibiotics as an outpatient. She is warned that unpleasant reactions
may occur if she consumes alcoholic beverages while taking this drug. The
antibiotic can be identified as which of the following?
A. Ceftriaxone
B. Doxycycline
C. Metronidazole
D. Ofloxacin
E. Pen G
Answer: C. Organisms associated with sexually transmitted diseases include
chlamydia, neisseria gonorrhea, treponema (syphilis), trichomonas, and
gardnerella vaginalis. The latter two organisms are effectively treated with
the drug metronidazole. Metronidazole has a chemical structure that results
in a disulfiram-like effect on aldehyde dehydrogenase, causing reactions with
ethanol. Patients should be cautioned not to consume alcoholic beverages
while on this drug
An 82-year-old hospitalized patient with creatinine clearance of 25 mL/min
has a microbial infection requiring treatment with antibiotics. Which of the
following drugs is least likely to require a dosage adjustment, either a smaller
dose than usual or an increased interval between doses?
A. Amphotericin B
B. Ceftriaxone
C. Gentamicin
D. Imipenem-cilastatin
E. Vancomycin
Answer: B. Ceftriaxone is eliminated largely via biliary excretion, and
decreases in renal function do not usually require a dose reduction. All of the
other antimicrobial drugs listed are eliminated by the kidney, at rates proportional to creatinine clearance, so major dose reductions would be needed in
patients with renal dysfunction to avoid toxicity.
What drug is most likely to be effective in most diseases caused by nematodes? A. Chloroquine B. Mebendazole C. Metronidazole D. Praziquantel E. Pyrimethamine
Answer: B. Mebendazole is the drug of choice for treatment of all nematode
infections (hookworm, roundworm, pinworm, whipworm). Pyrantel is
considered equally effective as mebendazole for nematodes. Praziquantel is
used for tapeworms (cestodes) and flukes (trematodes).
What antibiotic effectively treats a variety of causative organisms for bacterial pneumonia, and also works at the 50S ribosomal subunit? A. Azithromycin B. Ceftriaxone C. Doxycycline D. Ofloxacin E. Clindamycin
Answer: A. Macrolides (azithromycin) are effective for common causes of
pneumonias such as Strep pneumonia, Haemophilus influenza, Mycoplasma,
Legionella, and Chlamydophila. The drugs work at the 50S ribosomal subunit to inhibit translocation of the peptidyl tRNA from the acceptor to the
donor site.
In bacterial meningitis, third-generation cephalosporins are commonly
drugs of choice. However, in neonatal meningitis they would not provide
coverage if the infection was due to which of the following organisms?
A. Meningococci
B. L. monocytogenes
C. Pneumococci
D. E. coli
E. Group B streptococci
Answer: B. The most common pathogens implicated in bacterial meningitis in a neonate (age <1 month) are group B streptococci, followed by E.
coli. Meningococci and pneumococci become prevalent after 1 month of
age, and H. influenzae is becoming rarer since the availability of a vaccine.
A third-generation cephalosporin (e.g., cefotaxime) would be administered because it provides coverage for most of the organisms mentioned.
However, ampicillin is also needed to cover for Listeria monocytogenes, which
occurs with an incidence of 7 to 8% in neonatal meningitis.
Which one of the following drugs inhibits bacterial protein synthesis, preventing the translocation step via its interaction with the 50S ribosomal subunit? A. Clindamycin B. Gentamicin C. Chloramphenicol D. Imipenem E. Tetracycline
Answer: A. Clindamycin has a mechanism of action similar to, if not identical with, erythromycin and related macrolides. They bind to rRNA bases
on the 50S subunit to prevent translocation of peptidyl-mRNA from the
acceptor to the donor site. Chloramphenicol also binds to the 50S subunit
but interferes with the activity of peptidyltransferase. Gentamicin and
tetracyclines bind to the 30S ribosomal subunit. Imipenem is a cell-wall
synthesis inhibitor, acting similarly to beta-lactams.
Which of the following is a mechanism underlying the resistance of strains of
S. pneumoniae to the widely used antibiotic ciprofloxacin?
A. Reduced topoisomerase sensitivity to inhibitors
B. Increased synthesis of PABA
C. Formation of methyltransferases that change receptor structure
D. Structural changes in porins
E. Formation of drug-inactivating hydrolases
Answer: A. Microbial resistance to fluoroquinolones is increasing, and some
strains of Streptococcus pneumoniae are now resistant to ciprofloxacin.
The mechanism can involve changes in the structure of topoisomerase IV,
one of the “targets” of fluoroquinolones, which inhibit nucleic acid synthesis. Pneumococcal resistance to penicillins is also increasing via changes in
penicillin-binding proteins (PBPs). The other mechanisms listed underlie
microbial resistance to other antibiotics as follows: sulfonamides (choice B),
macrolides (choice C), extended-spectrum penicillins (choice D), and betalactams (choice E).
Gentamicin would be an ineffective drug for which of the following organisms? A. E. coli B. B. fragilis C. Pseudomonas D. Listeria if combined with ampicillin E. Proteus
Answer: B. Aminoglycosides like gentamicin work on aerobic gram negative
rods. They require oxygen to enter bacteria, and, as such, do not treat any
anaerobes including Bacteroides fragilis. They can be used with penicillins
such as ampicllin against Listeria for a synergistic effect.
In the treatment of a urinary tract infection in a patient known to have a deficiency of glucose-6-phosphate dehydrogenase, it would not be advisable to prescribe which of the following? A. Ciprofloxacin B. Amoxicillin C. Cephalexin D. Doxycycline E. Sulfamethoxazole
Answer: E. Drugs that cause oxidative stress may precipitate acute hemolysis
in patients who lack G6PD because they have a limited ability to generate NADPH, which restricts the formation of glutathione. Drugs in this
category include primaquine, quinine, nitrofurantoin, sulfonamides, and
TMP-SMX.
What is the most likely mechanism of resistance for methicillin-resistant
staphylococcus aureus to antistaph penicillins?
A. methylation of the binding site
B. active efflux of the drug from the bacteria
C. β-lactamase production
D. phosphorylation of the drug by bacterial enzymes
E. structural modifications of PBPs
Answer: E. Antistaph penicillins are inherently resistant to cleavage by bacterial beta-lactamases. Instead, resistance develops when the target for these
drug, PBPs, are altered such that the drug doesn’t bind effectively.
Highly active antiretroviral therapy (HAART) in HIV infection is associated with which of the following?
A. A decrease in viral mRNA copies/mL of blood
B. A decrease in the rate of emergence of drug resistance
C. A possible increase in CD4 cell count
D. A reduced incidence of opportunistic infections
E. All of the above
Answer: E. HAART in the management of HIV infection is reported
in many but not all patients to decrease viral load, increase CD4 cells,
slow disease progression, and reduce opportunistic infections. However,
in terms of the chemotherapy of AIDS, the word cure has little meaning.
Discontinuance of HAART, after suppression of viral RNA copies below
the sensitivity of the best current methods of analysis, is followed by the
reemergence of detectable viral RNA in the blood within a few months.
Oseltamivir and zanamivir are available for treatment of infections due to influenza A and B. The mechanism of their antiviral action is inhibition of which of the following? A. RNA polymerase B. Reverse transcriptase C. Thymidine kinase D. Neuraminidase E. Aspartate protease
Answer: D. Neuraminidase is an enzyme on the lipid envelope of influenza
A and B virions that prevents their clumping together and also their binding
to the surface of cells that have been already infected. Neuraminidase inhibitors interfere with this activity and reduce the availability of virions for entry
into noninfected cells. Oseltamivir and zanamivir decrease the severity and
duration of symptoms if given within a day or two of onset.
