First Aid USMLE Step 1: Pharmacology
(Complete)
Penicillin G (IV and IM)
Penicillin M (oral) Correct Answer: *MOA:*
*β-lactam*: a structural analog of D-ala-D-ala (a normal component of cell walls) which binds and
inactivates bacterial transpeptidases (penicillin-binding protein, PBPs) to block peptidoglycan cross
linking
*Clinical use:*
Bactericidal for Gram-⊕ cocci/rods, Gram-⊖ cocci (Neisseria), and spirochetes
Mostly used for Gram-⊕ organisms (S. pneumoniae, S. pyogenes, Actinomyces). Also used for Gram-⊖
cocci (mainly N. meningitidis) and spirochetes (namely T. pallidum). Bactericidal for Gram-⊕ cocci,
Gram-⊕ rods, Gram-⊖ cocci, and spirochetes. Penicillinase sensitive.
*Toxicity:*
Hypersensitivity reactions (type II), hemolytic anemia
*MOR:*
Penicilinase (a type of β-lactamase) in bacteria cleaves
Oxacillin
Nafcillin
Dicloxacillin Correct Answer: Penicillinase-resistant penicillins
*MOA:*
,Same as penicillin.
*Narrow spectrum*; penicillinase resistant because bulky R group blocks access of β-lactamase to β-
lactam ring.
*Clinical use:*
Bactericidal, narrow spectrum: *S. aureus* (except MRSA; resistant due to altered penicillin-binding
protein target site).
*Toxicity:*
Hypersensitivity reactions (type II), interstitial nephritis
"Use *naf* (*naf*cillin) for staph." Nafcillin has penetration to CNS
Aminopenicillins:
Ampicillin
Amoxicillin Correct Answer: Penicillinase-sensitive penicillins
*MOA:*
Same as penicillin.
Wider spectrum with better activity against Gram-⊖ bugs; penicillinase sensitive.
Administer with clavulanic acid to protect against destruction by β-lactamase.
*Clinical use:*
Bactericidal for Gram-⊕ cocci/rods, Gram-⊖ cocci, spirochetes; Extended-spectrum penicillin: *H.*
influenzae, *H.* pylori, *E.* coli, *L*isteria monocytogenes, *P*roteus mirabilis, *S*almonella,
*S*higella, enterococci. *HHELPSS*
*Toxicity:*
,Hypersensitivity reactions (type II), ampicillin rash (often with EBV infection- reaction-not an allergy),
pseudomembranous colitis
*MOR:*
β-lactamase activity
Ticarcillin
Piperacillin Correct Answer: Ureidopenicillins: "Antipseudomonals"
*MOA:*
Same as penicillin. Extended spectrum.
*Clinical use:*
*Pseudomonas spp.* and Gram-⊖ rods
Hospital-acquired pneumonias (Klebsiella, H. influenzae, Enterobacter)
Susceptible to penicillinase; use with β-lactamase inhibitors.
*Toxicity:*
Hypersensitivity reactions (type II)
Clavulanic Acid
Sulbactam
Tazobactam Correct Answer: *MOA:*
β-lactamase inhibitors
*Clinical use:*
, Often added to penicillin antibiotics (aminopenicillins, antipseudomonals) to protect the antibiotic from
destruction by β-lactamase (penicillinase).
"*CAST*" - *C*lavulanic *A*cid, *S*ulbactam, *T*azobactam
Cefadroxil
Cephalexin
Cephradine (PO)
Cefazolin (IV)
Cefazolin
Cephalexin Correct Answer: *1st Generation Cephalosporins*
*MOA:*
Same as that of penicillins
*Clinical use:*
Gram-⊕ cocci: streptococci, methicillin-susceptible staphylococci
Community-acquired strains of enteric Gram-⊖ rods, *P*roteus spp., *E. c*oli, *K*lebsiella spp.
(*PEcK*)
Cefazolin: used prior to surgery to prevent S. aureus wound infections.
*Toxicity:*
Hypersensitivity reactions, autoimmune hemolytic anemia, disulfiram-like reaction, vitamin K deficiency.
Exhibit cross-reactivity with penicillins. Potentiate the nephrotoxicity of aminoglycosides.
*MOR:*
Structural change in penicillin-binding proteins (transpeptidases).
(Complete)
Penicillin G (IV and IM)
Penicillin M (oral) Correct Answer: *MOA:*
*β-lactam*: a structural analog of D-ala-D-ala (a normal component of cell walls) which binds and
inactivates bacterial transpeptidases (penicillin-binding protein, PBPs) to block peptidoglycan cross
linking
*Clinical use:*
Bactericidal for Gram-⊕ cocci/rods, Gram-⊖ cocci (Neisseria), and spirochetes
Mostly used for Gram-⊕ organisms (S. pneumoniae, S. pyogenes, Actinomyces). Also used for Gram-⊖
cocci (mainly N. meningitidis) and spirochetes (namely T. pallidum). Bactericidal for Gram-⊕ cocci,
Gram-⊕ rods, Gram-⊖ cocci, and spirochetes. Penicillinase sensitive.
*Toxicity:*
Hypersensitivity reactions (type II), hemolytic anemia
*MOR:*
Penicilinase (a type of β-lactamase) in bacteria cleaves
Oxacillin
Nafcillin
Dicloxacillin Correct Answer: Penicillinase-resistant penicillins
*MOA:*
,Same as penicillin.
*Narrow spectrum*; penicillinase resistant because bulky R group blocks access of β-lactamase to β-
lactam ring.
*Clinical use:*
Bactericidal, narrow spectrum: *S. aureus* (except MRSA; resistant due to altered penicillin-binding
protein target site).
*Toxicity:*
Hypersensitivity reactions (type II), interstitial nephritis
"Use *naf* (*naf*cillin) for staph." Nafcillin has penetration to CNS
Aminopenicillins:
Ampicillin
Amoxicillin Correct Answer: Penicillinase-sensitive penicillins
*MOA:*
Same as penicillin.
Wider spectrum with better activity against Gram-⊖ bugs; penicillinase sensitive.
Administer with clavulanic acid to protect against destruction by β-lactamase.
*Clinical use:*
Bactericidal for Gram-⊕ cocci/rods, Gram-⊖ cocci, spirochetes; Extended-spectrum penicillin: *H.*
influenzae, *H.* pylori, *E.* coli, *L*isteria monocytogenes, *P*roteus mirabilis, *S*almonella,
*S*higella, enterococci. *HHELPSS*
*Toxicity:*
,Hypersensitivity reactions (type II), ampicillin rash (often with EBV infection- reaction-not an allergy),
pseudomembranous colitis
*MOR:*
β-lactamase activity
Ticarcillin
Piperacillin Correct Answer: Ureidopenicillins: "Antipseudomonals"
*MOA:*
Same as penicillin. Extended spectrum.
*Clinical use:*
*Pseudomonas spp.* and Gram-⊖ rods
Hospital-acquired pneumonias (Klebsiella, H. influenzae, Enterobacter)
Susceptible to penicillinase; use with β-lactamase inhibitors.
*Toxicity:*
Hypersensitivity reactions (type II)
Clavulanic Acid
Sulbactam
Tazobactam Correct Answer: *MOA:*
β-lactamase inhibitors
*Clinical use:*
, Often added to penicillin antibiotics (aminopenicillins, antipseudomonals) to protect the antibiotic from
destruction by β-lactamase (penicillinase).
"*CAST*" - *C*lavulanic *A*cid, *S*ulbactam, *T*azobactam
Cefadroxil
Cephalexin
Cephradine (PO)
Cefazolin (IV)
Cefazolin
Cephalexin Correct Answer: *1st Generation Cephalosporins*
*MOA:*
Same as that of penicillins
*Clinical use:*
Gram-⊕ cocci: streptococci, methicillin-susceptible staphylococci
Community-acquired strains of enteric Gram-⊖ rods, *P*roteus spp., *E. c*oli, *K*lebsiella spp.
(*PEcK*)
Cefazolin: used prior to surgery to prevent S. aureus wound infections.
*Toxicity:*
Hypersensitivity reactions, autoimmune hemolytic anemia, disulfiram-like reaction, vitamin K deficiency.
Exhibit cross-reactivity with penicillins. Potentiate the nephrotoxicity of aminoglycosides.
*MOR:*
Structural change in penicillin-binding proteins (transpeptidases).
