Mechanism of action of sirolimus (rapamycin) is:

Correct Answer: C

Rationale: The correct answer is C: Inhibits calcineurin. Sirolimus inhibits the mTOR pathway by binding to FKBP12 and forming a complex that inhibits the activity of mTOR complex 1. Calcineurin is not directly involved in the mechanism of action of sirolimus. Choice A is incorrect because sirolimus does not involve anti-idiotype antibodies. Choice B is incorrect because sirolimus does not modulate the CD3 receptor. Choice D is incorrect because sirolimus does not mediate ADCC towards T lymphocytes.

Correct Answer: A

Rationale: The correct answer is A because nicotinic acid (niacin) increases the rate of catabolism of VLDL by inhibiting lipolysis in adipose tissue, leading to decreased free fatty acids available for VLDL synthesis. This results in decreased VLDL production and increased clearance, thus lowering plasma VLDL levels. Option B is incorrect because nicotinic acid does not decrease VLDL catabolism. Option C is incorrect as not all choices are correct. Option D is incorrect as there is a correct answer.

Correct Answer: A

Rationale: Rationale: A: Correct. Calcitriol regulates calcium and phosphate levels, leading to potential ectopic calcification. Monitoring is crucial. B: Incorrect. Calcitriol does undergo enterohepatic circulation. C: Incorrect. Calcitriol is not toxic to osteoclasts; it has a role in bone health. D: Incorrect. Calcitriol has a complex relationship with bioavailability, affected by several factors.

Correct Answer: C

Rationale: Rationale: Hydrochlorothiazide blocks NaCl cotransporters in the distal tubule, reducing sodium reabsorption and increasing diuresis. Acetazolamide inhibits carbonic anhydrase in the proximal tubule. Furosemide inhibits the Na-K-2Cl cotransporter in the thick ascending limb. Spironolactone is a mineralocorticoid receptor antagonist acting on the principal cells of the collecting duct. Therefore, the correct answer is C, as it directly targets the distal tubule's mechanism of sodium reabsorption.

Correct Answer: C

Rationale: The correct answer is C: Imipenem, as it belongs to the carbapenem class of antibiotics. Carbapenems are broad-spectrum antibiotics effective against a wide range of bacteria, including some that are resistant to other antibiotics. Imipenem is specifically known for its activity against gram-positive and gram-negative bacteria. A: Aztreonam is a monobactam antibiotic, not a carbapenem. B: Amoxicillin is a penicillin antibiotic, not a carbapenem. D: Clarithromycin is a macrolide antibiotic, not a carbapenem. In summary, only Imipenem (Choice C) is a carbapenem antibiotic, making it the correct choice for this question.