Indication for plicamycin (formerly mithramycin) administration is:

Correct Answer: D

Rationale: The correct answer is D because plicamycin is indicated for testicular cancers refractory to standard treatment, Paget’s disease, and hypercalcemia of malignancy. Plicamycin inhibits bone resorption and reduces serum calcium levels in patients with hypercalcemia of malignancy. It also has cytotoxic effects on certain types of cancer cells, including testicular cancers. Therefore, it is used for all of the mentioned conditions. Choices A, B, and C are incorrect because plicamycin is not limited to only one specific condition, but rather can be used for multiple indications.

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: A

Rationale: The correct answer is A: Metronidazole and diloxanide. Metronidazole is effective against the invasive form of Entamoeba histolytica, the parasite causing amebiasis. Diloxanide is used to eliminate the non-invasive cyst form of the parasite in the intestine. Streptomycin (choice B) is not effective against amebiasis. Iodoquinol (choice C) is used for non-invasive amebiasis but not the intestinal form. Emetine (choice D) is reserved for extraintestinal disease and is not commonly used due to its toxicity.

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.