Which of the following antivitamins prevent a vitamin B6 from exerting its typical metabolic effects?

Correct Answer: D

Rationale: The correct answer is D: All of the above. Isoniazide, ethanol, and carbamazepine are all antivitamins that interfere with the metabolism of vitamin B6. Isoniazide inhibits the conversion of vitamin B6 to its active form, ethanol decreases the absorption and utilization of vitamin B6, and carbamazepine reduces the plasma levels of vitamin B6. Therefore, all three choices prevent vitamin B6 from exerting its metabolic effects. The other choices are incorrect because each of them individually interferes with the action of vitamin B6.

Correct Answer: A

Rationale: The correct answer is A: Hepatic toxicity. Dihydrotachysterol is a vitamin D analog used to treat hypoparathyroidism and hypocalcemia. It can cause liver damage as a side effect due to its metabolism in the liver. General malaise (B), lymphocytopenia (C), and hypertension (D) are not typically associated with dihydrotachysterol use. Therefore, the correct answer is A based on the drug's mechanism of action and known side effects.

Correct Answer: C

Rationale: Rationale: Chronic use of Furosemide can lead to distal tubular hypertrophy, reducing its diuretic effect due to compensatory changes in the nephron function. Furosemide is a loop diuretic acting in the thick ascending limb of the loop of Henle. Acetazolamide is a carbonic anhydrase inhibitor acting in the proximal tubule. Amiloride is a potassium-sparing diuretic acting on the collecting duct. Hydrochlorothiazide is a thiazide diuretic acting in the distal convoluted tubule. Only Furosemide among the options affects the loop of Henle, leading to distal tubular hypertrophy over time.

Correct Answer: B

Rationale: The correct answer is B: Lincomycin. Lincomycin belongs to the lincosamides class of antibiotics, which also includes clindamycin. Lincomycin works by inhibiting bacterial protein synthesis. Erythromycin (A) is a macrolide antibiotic, not a lincosamide. Azithromycin (C) is another macrolide antibiotic. Aztreonam (D) is a monobactam antibiotic, not a lincosamide. Therefore, the correct answer is B because it is the only drug belonging to the lincosamides class.

Correct Answer: B

Rationale: Step 1: Isoniazid is a hydrazide of isonicotinic acid, making it the correct antimycobacterial drug. Step 2: Rifampin is a rifamycin antibiotic, not a hydrazide of isonicotinic acid. Step 3: Ethambutol is an antimycobacterial drug but not a hydrazide of isonicotinic acid. Step 4: Pyrazinamide is an antimycobacterial drug but not a hydrazide of isonicotinic acid.