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USMLE
New FA Micro 3
| Question | Answer |
|---|---|
| block nucleotide synthesis | sulfonamides, trimethoprim |
| block DNA topoisomerases | quinolones |
| block mRNA synthesis | rifampin |
| block protein synthesis at 50S ribosomal subunit | chloramphenicol, erythromycin/macrolides, lincomycin, clindamycin, streptogramins (quinupristin, dalfopristin), linezolid |
| block protein synthesis at 30S ribosomal subunit | aminoglycosides, tetracyclines |
| bacteriacidal antibiotics (6) | penicilin, cephalosporins, vancomycin, aminoglycosides, fluoroquinolones, metronidazole |
| penicillin mechanism | bind PBPs, block transpeptidase cross-linking of cell wall; activate autolytic enzymes |
| penicillin toxicity | hypersensitivity reactions, hemolytic anemia |
| mechanism of methicillin, nafcillin, dicloxacillin | bind PBPs, block transpeptidase cross-linking of cell wall - penicillinase resistant because of bulkier R group |
| methicillin toxicity | interstitial nephritis |
| ampicillin, amoxicillin toxicity | hypersensitvity, ampicillin rash (esp. in pts. w/ mono), pseudomembranous colitis |
| ticarcillin, carbenicillin, piperacillin usage | pseudomonas (Takes Care of Pseudomonas) |
| mechanism of cephalosporins | beta-lactam drugs that inhibit cell wall synthesis - less susceptible to penicillinases |
| antibiotic for penicillin-allergic patients and patients w/ renal toxicity who can't tolerate aminoglycosides | aztreonam (synergistic w/ aminoglycosides) |
| drug of choice for enterobacter | imipenem/cilastin |
| antibiotic that can cause seizures at high plasma levels | imipenem/cilastin |
| mechanism of vancomycin | inhibits cell wall mucopeptide formation by binding D-ala D-ala portion of cell wall precursors |
| mechanism of resistance to vancomycin | amino acid change of D-ala D-ala to D-ala D-lac |
| vancomycin toxicity | well tolerated in general - does NOT have many problems: nephrotoxicity, ototoxicity, thrombophlebitis |
| aminoglycosides | streptomycin, gentamicin, tobramycin, amikacin - bacteriacidal |
| mechanism of action of aminoglycosides | inhibit 30S subunit - inhibit formation of initiation complex and cause misreading of mRNA |
| are aminoglycosides effective agains anaerobes? | no! require O2 or uptake |
| aminoglycosides cause nephrotoxicity especially when used in combination with _________ | cephalosporins |
| aminoglycosides cause ototoxicity especially when used with_________ | loop diuretics |
| are aminoglycosides safe to use in pregnancy? | no! teratogenic |
| which tetracycline can be used in patients with renal failure? | doxycycline because it is fecally eliminated |
| can you take tetracyclines with milk? | no! nor atacids or iron-containing preparations because divalent cations inhibit its absorption in the gut |
| tetracycline toxicity | discoloration of teeth and inhibition of bone growth in children, photosensitivity |
| mechanism of action of macrolides | inhibit protein synthesis by blocking translocation - bind to 23S rRNA of the 50S subunit |
| name 3 macrolides | erythromycin, azithromycin, clarithromycin |
| when can sulfonamides cause hemolysis? | G6PD deficiency |
| most common cause of noncompliance with macrolides | GI discomfort |
| macrolides increase the serum concentration of what drugs? | theophyllines, oral anticoagulants |
| acute cholestatic hepatitis & eosinophilia are toxicities of which class of antibiotics? | macrolides |
| clinical use of chloramphenicol | meningitis - H. flu, neisseria, strep pneumo |
| why does chloramphenicol cause gray baby syndrome? | because infants lack liver UDP-glucoronyl transferase |
| is the aplastic anemia seen with chloramphenicol dose dependent? | no! the anemia is, however |
| mechanism of action of chloramphenicol | inhibits 50S peptidyltransferase |
| what is the clinical use of clindamycin? | treatment of anaerobic infections - B. frag, C. perfringfens |
| clindamycin toxicity | pseudomembranous colitis - destroys normal GI flora |
| mechanism of action of sulfonamides (sulfamethoxazole, sulfisoxazole, triple sulfas, etc.) | PABA antimetabolites inhibit dihydropteroate synthase |
| what side effect can sulfonamides cause in infants? | kernicterus |
| mechanism of action of trimethoprim | inhibits bacterial dihydrofolate reductase |
| trimethoprim toxicity | megaloblastic anemia, leukopenia, granulocytopenia (may alleviate with supplemental folinic acid) |
| mechanism of action of fluoroquinolones | inhibit DNA gyrase (topoisomerase II) |
| what class of antibiotics can cause cartilage damage in kids? | fluoroquinolones |
| what drug is associated with a disulfiram-like reaction with alcohol and a metallic taste | metronidazole |
| what can prevent the neurotoxicity associated with INH? | pyridoxine (vitamin B6) |
| INH toxicity | hemolysis if G6PD deficient, neurotoxicity, hepatotoxicity, SLE-like syndrome |
| mechanism of action of rifampin | inhibits DNA-dependent RNA polymerase |
| what drug delays resistance to dapsone when used for leprosy? | rifampin |
| resistance mechanism for penicillins/cephalosporins | beta-lactamase cleavage of beta lactam ring |
| resistance mechanism for aminoglycosides | modification via acetylation, adenylation, or phosphorylation |
| resistance mechanism for chloramphenicol | modification via acetylation |
| resistance mechanism for macrolides | methylation of rRNA near erythromycin's ribosome binding site |
| resistance mechanism for tetracycline | decreased uptake or increased transport out of cell |
| resistance mechanism for sulfonamides | altered enzyme (bacterial dihydropteroate synthetase), decreased uptake, or increased PABA synthesis |
| mechanism of action of amphotericin B | binds ergosterol (unique to fungi); forms membrane pores that allow leakage of electrolytes and disrupt homeostasis |
| drug of choice for systemic mycoses | amphotericin B |
| amphotericin B toxicity | fever/chills, hypotension, nephrotoxicity, arrhythmias, hypochromic normocytic anemia |
| do ketoconazole and ampho B act synergistically? | no - they antagonize each other's actions, so should never be used together |
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Asclepius
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