FIRST AID USMLE STEP 1:
PHARMACOLOGY (COMPLETE)
EXAM 2025 QUESTIONS AND
ANSWERS
Penicillin G (IV and IM)
Penicillin M (oral) - ....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.
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,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 - ....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:*
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,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 - ....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:*
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, 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 - ....ANSWER ...-Ureidopenicillins: "Antipseudomonals"
*MOA:*
Same as penicillin. Extended spectrum.
*Clinical use:*
*Pseudomonas spp.* and Gram-⊖ rods
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 4
PHARMACOLOGY (COMPLETE)
EXAM 2025 QUESTIONS AND
ANSWERS
Penicillin G (IV and IM)
Penicillin M (oral) - ....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.
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 1
,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 - ....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:*
....COPYRIGHT ©️ 2025 ALL RIGHTS RESERVED...TRUSTED & VERIFIED 2
,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 - ....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:*
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, 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 - ....ANSWER ...-Ureidopenicillins: "Antipseudomonals"
*MOA:*
Same as penicillin. Extended spectrum.
*Clinical use:*
*Pseudomonas spp.* and Gram-⊖ rods
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