Delayed allergy reaction (type IV allergic reaction) is:

Correct Answer: B

Rationale: Delayed allergy reaction (type IV allergic reaction) is characterized by a delayed onset, typically appearing hours after exposure. This differs from immediate allergic reactions (type I) that occur within minutes. Choice A refers to an immediate allergic response. Choice C describes type III allergic reactions involving antigen-antibody complexes, not type IV. Choice D is related to tissue damage caused by elevated antigen-antibody complexes, which is not specific to delayed allergy reactions. Thus, choice B is correct as it aligns with the delayed nature of type IV allergic reactions.

Correct Answer: B

Rationale: The correct answer is B, Allopurinol. Allopurinol is a xanthine oxidase inhibitor, which helps reduce uric acid levels in conditions like gout. Xanthine oxidase is an enzyme involved in the production of uric acid. Physostigmine (A) is a cholinesterase inhibitor used in conditions like myasthenia gravis. Aminocaproic acid (C) is an antifibrinolytic agent. Acetazolamide (D) is a carbonic anhydrase inhibitor used in conditions like glaucoma and altitude sickness. Therefore, Allopurinol is the correct choice as a xanthine oxidase inhibitor.

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.