Repeated USMLE Questions Step 1 Review-149- Pharmacology

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Q- A 25-year-old woman is taking oral contraceptive pills (OCPs). Which antibiotic can decrease the effectiveness of her contraceptive therapy?

A- Amoxicillin

B- Azithromycin

C- Ciprofloxacin

D- Rifampin

D- Rifampin- Rifampin induces hepatic enzymes, increasing the metabolism of estrogen and progestin, thus reducing OCP efficacy.

 

Q- A 60-year-old man with benign prostatic hyperplasia (BPH) and hypertension is prescribed terazosin. Which of the following adverse effects should he be warned about?

A- constipation

B- Orthostatic hypotension

C- Reflex bradycardia

D- Sedation

B- Orthostatic hypotension- α₁-blockers like terazosin cause relaxation of vascular smooth muscle, leading to postural hypotension, especially after the first dose.

 

 

Q- Which of the following is the mechanism of action of botulinum toxin at cholinergic nerve terminals?

A- Activates muscarinic receptors directly

B- Inhibits acetylcholine release by preventing SNARE protein function

C- Blocks acetylcholine reuptake

D- Blocks acetylcholine synthesis by inhibiting choline acetyltransferase

E- Stimulates excessive acetylcholine release at the neuromuscular junction

B- Inhibits acetylcholine release by preventing SNARE protein function- Botulinum toxin cleaves SNARE proteins (such as SNAP-25), which are required for vesicle fusion and acetylcholine release at cholinergic nerve terminals. This leads to flaccid paralysis. Other options do not describe its true mechanism.

 

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