Antivitamins are:

Correct Answer: B

Rationale: The correct answer is B because antivitamins are substances that interfere with the absorption, metabolism, or utilization of vitamins, preventing them from exerting their typical metabolic effects. This definition directly aligns with the concept of antivitamins. Option A is incorrect because it describes vitamins themselves, not antivitamins. Option C describes enzymes, not antivitamins. Option D refers to coenzymes, which are necessary for enzyme function, but it does not accurately define antivitamins. Thus, B is the correct choice.

Correct Answer: B

Rationale: Step 1: Lovastatin inhibits HMG-CoA reductase, an enzyme involved in cholesterol synthesis. Step 2: Inhibiting HMG-CoA reductase leads to upregulation of LDL receptors, enhancing LDL clearance. Step 3: Therefore, Lovastatin both inhibits an enzyme and indirectly enhances LDL clearance. Summary: A: Cholestyramine binds bile acids, not related to LDL clearance. C: Nicotinic acid primarily affects HDL levels, not directly related to LDL clearance. D: Probucol mainly acts by increasing HDL levels, not directly related to LDL clearance.

Correct Answer: D

Rationale: The correct answer is D: Intravenous. Pamidronate is a bisphosphonate used to treat bone diseases like osteoporosis. Intravenous route ensures rapid and complete absorption, leading to optimal therapeutic effects. Oral administration (A) would result in poor bioavailability. Subcutaneous (B) and intranasal (C) routes are not commonly used for pamidronate due to inconsistent absorption and inadequate therapeutic levels. Therefore, intravenous administration is the preferred route for pamidronate to achieve the desired clinical outcomes.

Correct Answer: B

Rationale: The correct answer is B: Thiazide diuretics. Thiazide diuretics act in the distal convoluted tubule by inhibiting the sodium-chloride symporter, leading to increased sodium and water excretion. This results in decreased blood volume and reduced blood pressure. Loop diuretics (A) act in the loop of Henle, potassium-sparing diuretics (C) act in the collecting duct, and carbonic anhydrase inhibitors (D) act in the proximal convoluted tubule. Thiazide diuretics are preferred for conditions like hypertension and edema due to their efficacy and site of action in the distal convoluted tubule.

Correct Answer: A

Rationale: The correct answer is A: Inhibition of transpeptidation in the bacterial cell wall. Penicillins work by inhibiting the enzyme transpeptidase, which is involved in the cross-linking of peptidoglycan chains in the bacterial cell wall. This leads to weakened cell walls, causing bacterial cell lysis. Choices B, C, and D are incorrect because penicillins do not inhibit beta-lactamase (choice B), activate endogenous proteases to destroy the cell wall (choice C), or activate endogenous phospholipases altering cell membrane permeability (choice D). The primary mechanism of action of penicillins is through interfering with cell wall synthesis, making choice A the correct answer.