1 Exampromax - Stuvia US 2025/2026
First Aid USMLE Step 1: Pharmacology (Complete)
Questions with Detailed Verified Answers (100% Correct
Answers) /Already Graded A+
Penicillin G (IV and IM)
Penicillin M (oral)
Ans: *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:*
Exampromax - Stuvia US
Bactericidal for Gram-⊕ cocci/rods, Gram-⊖ cocci (Neisseria), and
spirochetes
Approved By:
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
, 2 Exampromax - Stuvia US 2025/2026
Ans: 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
Exampromax - Stuvia US
Approved By:
"Use *naf* (*naf*cillin) for staph." Nafcillin has penetration to CNS
Aminopenicillins:
Ampicillin
Amoxicillin
, 3 Exampromax - Stuvia US 2025/2026
Ans: 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*
Exampromax - Stuvia US
Approved By:
*Toxicity:*
Hypersensitivity reactions (type II), ampicillin rash (often with EBV
infection- reaction-not an allergy), pseudomembranous colitis
*MOR:*
β-lactamase activity
Ticarcillin
Piperacillin
, 4 Exampromax - Stuvia US 2025/2026
Ans: 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)
Exampromax - Stuvia US
Clavulanic Acid
Approved By:
Sulbactam
Tazobactam
Ans: *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
First Aid USMLE Step 1: Pharmacology (Complete)
Questions with Detailed Verified Answers (100% Correct
Answers) /Already Graded A+
Penicillin G (IV and IM)
Penicillin M (oral)
Ans: *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:*
Exampromax - Stuvia US
Bactericidal for Gram-⊕ cocci/rods, Gram-⊖ cocci (Neisseria), and
spirochetes
Approved By:
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
, 2 Exampromax - Stuvia US 2025/2026
Ans: 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
Exampromax - Stuvia US
Approved By:
"Use *naf* (*naf*cillin) for staph." Nafcillin has penetration to CNS
Aminopenicillins:
Ampicillin
Amoxicillin
, 3 Exampromax - Stuvia US 2025/2026
Ans: 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*
Exampromax - Stuvia US
Approved By:
*Toxicity:*
Hypersensitivity reactions (type II), ampicillin rash (often with EBV
infection- reaction-not an allergy), pseudomembranous colitis
*MOR:*
β-lactamase activity
Ticarcillin
Piperacillin
, 4 Exampromax - Stuvia US 2025/2026
Ans: 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)
Exampromax - Stuvia US
Clavulanic Acid
Approved By:
Sulbactam
Tazobactam
Ans: *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
