Mechanism of sulfonamides’ antibacterial effect is:

Correct Answer: B

Rationale: The correct answer is B: Inhibition of dihydropteroate synthase. Sulfonamides work by inhibiting dihydropteroate synthase, an enzyme involved in the folate synthesis pathway in bacteria. This disruption leads to a decrease in production of essential nucleotides, ultimately inhibiting bacterial growth. A: Inhibition of dihydropteroate reductase is incorrect as sulfonamides target dihydropteroate synthase, not reductase. C: Inhibition of cyclooxygenase is incorrect as this mechanism is related to NSAIDs, not sulfonamides. D: Activation of DNA gyrase is incorrect as this mechanism is associated with antibiotics like fluoroquinolones, not sulfonamides.

Correct Answer: B

Rationale: Fluorouracil is an antimetabolite that interferes with DNA and RNA synthesis. It is used to treat various cancers by inhibiting cell growth. This makes option B the correct choice. Antibiotics (A) target bacteria, not cancer cells. Plant alkaloids (C) are derived from plants and have different mechanisms of action. Bone marrow growth factors (D) stimulate the production of blood cells but do not directly inhibit cancer cell growth.

Correct Answer: B

Rationale: The correct answer is B: Verapamil. Verapamil is a calcium channel blocker that acts on acetylcholine-sensitive K+ channels, leading to smooth muscle relaxation and vasodilation. Digoxin (A) acts on cardiac muscle by inhibiting the sodium-potassium pump. Propranolol (C) is a beta-blocker that acts on beta-adrenergic receptors. Procainamide (D) is a Class I antiarrhythmic agent that blocks sodium channels. Thus, Verapamil is the correct choice based on its mechanism of action on acetylcholine-sensitive K+ channels.

Correct Answer: B

Rationale: The correct answer is B: Add nitroglycerin to the therapeutic regimen. Nitroglycerin is a standard treatment for variant angina as it helps dilate blood vessels, increasing blood flow to the heart. This can help relieve chest pain associated with the condition. Choice A is incorrect as nifedipine and propranolol are both used to treat angina, but nifedipine is not specifically indicated for variant angina. Choice C is incorrect as captopril is an ACE inhibitor used for hypertension and heart failure, not specifically for variant angina. Choice D is incorrect as nifedipine and hydrochlorothiazide are both used for hypertension but not specifically for variant angina.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.