USMLE step 3 - drug MOA (indications) Exam Questions and Answers

USMLE step 3 - drug MOA (indications) Erythromycin - Answer-50S ribosome, inhibits TRANSLOCATION (movement of tRNA-aa from acceptor site to peptidyl site) clindamycin, chloramphenicol - Answer-50 ribosome, inhibits PEPTIDYL TRANSFERASE (incorporation of new a.a.'s into growing strand) linezolid - Answer-50S protein synthesis inhibitor tetracycline - Answer-30S ribosome, blocks tRNA-aa from binding to ACCEPTOR SITE on mRNA aminoglycosides - Answer-30S ribosome, blocks INITIATION of translation and induces PREMATURE TERMINATION or mistranslation vancomycin - Answer-binds D-ala-D-ala portion of cell wall precursors, prevents POLYMERIZATION OF PEPTIDOGLYCANS cephalosporins - Answer-beta-lactam, with with some resistance to penicillinase ampicillin, amoxicillin - Answer-beta-lactam, broader spectrum but still susceptible to penicillinase ticarcillin, piperacillin - Answer-beta-lactam, broad-spectrum rifampin - Answer-blocks mRNA transcription by inhibiting mRNA POLYMERASE beta subunit metronidazole - Answer-interacts with microbial ferredoxins to produce CYTOTOXIC INTERMEDIATES fluoroquinolones - Answer-inhibits DNA GYRASE (controls supercoiling) and TOPOISOMERASE (untangling interlocked daughter chromosomes) trimethroprim - Answer-inhibits DIHYDROFOLATE REDUCTASE --> decreased syntesis of thymidylate, purine nucleotides, amino acids penicillin (beta-lactam) - Answer-1) bind PBPs 2) block TRANSPEPTIDASE cross-linking of peptidoglycan 3) activate AUTOLYTIC ENZYMES clavalunic acid, sulbactam, tazobactam - Answer-beta-lactamase inhibitors statins - Answer-HMGCoA REDUCTASE inhibitor -->decreased hepatic cholesterol synth --> increased LDL receptor expression --> dec LDL