Coenzymes are:

Correct Answer: D

Rationale: The correct answer is D because coenzymes are nonprotein organic substances that combine with specific apoenzymes to form active enzyme systems. This is essential for catalyzing biochemical reactions. Choice A describes vitamins, not coenzymes. Choice B describes anti-nutrients, not coenzymes. Choice C describes enzymes, not coenzymes. Thus, the correct answer is D.

Correct Answer: A

Rationale: Rationale: Cholestyramine binds bile acids in the GI tract, preventing their reabsorption and promoting excretion. This helps lower cholesterol levels. Nicotinic acid, gemfibrozil, and probucol work through different mechanisms and are not bile acid binders. Nicotinic acid lowers LDL and triglycerides, gemfibrozil decreases triglycerides, and probucol increases HDL. Therefore, the correct answer is A.

Correct Answer: B

Rationale: The correct answer is B because pamidronate has a skeletal half-life of about 10 years, not 24 hours. A: Pamidronate is not available orally due to poor bioavailability and potential esophageal irritation. C: Fever and lymphocytopenia are reversible side effects of pamidronate. D: Pamidronate can irritate the esophagus if not washed down promptly to the stomach, leading to esophageal ulceration.

Correct Answer: C

Rationale: The correct answer is C: Potassium-sparing diuretics. Potassium-sparing diuretics act in the collecting tubules by blocking the sodium-potassium exchange, leading to decreased sodium reabsorption and potassium retention. This mechanism helps to promote diuresis while preventing potassium loss. Loop diuretics (A) act in the loop of Henle, thiazide diuretics (B) act in the distal convoluted tubule, and carbonic anhydrase inhibitors (D) act in the proximal convoluted tubule. Therefore, they are not directly involved in the collecting tubules like potassium-sparing diuretics.

Correct Answer: D

Rationale: The correct answer is D (All of the above) because all three choices (Clavulanic acid, Sulbactam, Tazobactam) are beta-lactamase inhibitors commonly co-administered with penicillins to enhance their efficacy. Beta-lactamase inhibitors work by inhibiting bacterial enzymes that can inactivate penicillins, allowing the antibiotic to remain effective against the bacteria. Clavulanic acid, Sulbactam, and Tazobactam are specifically designed to counteract beta-lactamase enzymes produced by bacteria, making them effective choices for combination therapy with penicillins. The other choices (A, B, C) are incorrect as each of them alone is a valid beta-lactamase inhibitor used in clinical practice.