Mechanism of action of tacrolimus (FK-506) is:

Correct Answer: D

Rationale: Rationale for Choice D (Inhibits calcineurin): 1. Tacrolimus binds to FK-binding protein, forming a complex that inhibits calcineurin. 2. Calcineurin inhibition blocks T-cell activation by preventing dephosphorylation of NFAT, hindering IL-2 production. 3. This suppresses immune response in transplant recipients. Summary: A: Inhibiting CD3 receptor is the mechanism of action of other drugs like anti-CD3 antibodies, not tacrolimus. B: Complement-mediated cytolysis is unrelated to tacrolimus. C: Substitution for deficient immunoglobulins is not the mechanism of action of tacrolimus, which targets T-cell activation.

Correct Answer: B

Rationale: Step 1: Clofibrate is associated with higher rates of adverse effects and drug interactions compared to gemfibrozil. Step 2: Gemfibrozil has been shown to be more effective in lowering triglyceride levels. Step 3: Studies have demonstrated that gemfibrozil reduces the risk of cardiovascular events more effectively than clofibrate. Step 4: Therefore, the correct answer is B (FALSE) as gemfibrozil is generally regarded as superior to clofibrate based on safety and efficacy data.

Correct Answer: D

Rationale: The correct answer is D: All of the above. 1. Primary hyperparathyroidism can lead to increased excretion of phosphate in the urine, causing hypophosphatemia. 2. Vitamin D deficiency can result in impaired absorption of phosphate in the intestines, contributing to hypophosphatemia. 3. Idiopathic hypercalciuria can lead to excessive excretion of both calcium and phosphate in the urine, further exacerbating hypophosphatemia. In summary, all three conditions (A, B, and C) are associated with hypophosphatemia due to different mechanisms involving impaired phosphate balance in the body.

Correct Answer: C

Rationale: Step-by-step rationale for why choice C is correct: 1. Hydrochlorothiazide is a diuretic commonly used to treat hypertension. 2. Amiloride is a potassium-sparing diuretic often used in combination with hydrochlorothiazide. 3. Fixed-dose combinations of both drugs are effective in managing essential hypertension. 4. Therefore, choice C, "Both of the above," is correct as it includes both hydrochlorothiazide and amiloride. Summary: - Choice A is incorrect because hydrochlorothiazide alone is not always part of fixed-dose combinations for essential hypertension. - Choice B is incorrect because amiloride alone is not commonly used to treat essential hypertension. - Choice D is incorrect because both hydrochlorothiazide and amiloride can be part of fixed-dose combinations for essential hypertension.

Correct Answer: C

Rationale: The correct answer is C: Glycopeptides. Glycopeptides inhibit bacterial cell wall synthesis, not protein synthesis. Macrolides (A), Aminoglycosides (B), and Tetracyclines (D) all inhibit protein synthesis at different stages, making them effective antibiotics against bacterial infections. Glycopeptides specifically target cell wall synthesis by binding to D-alanyl-D-alanine terminus of the growing peptidoglycan chain, leading to cell lysis. Therefore, Glycopeptides do not directly interfere with protein synthesis, distinguishing them from the other antibiotics listed.