H2 histamine receptor subtype is distributed in:

Correct Answer: B

Rationale: The correct answer is B because H2 histamine receptor subtype is mainly distributed in gastric mucosa, cardiac muscle, mast cells, and brain. This receptor subtype plays a crucial role in gastric acid secretion and cardiovascular functions. Choice A is incorrect because smooth muscle and endothelium are primarily associated with H1 receptors, not H2 receptors. Choice C is incorrect because presynaptic H3 receptors are found in the brain and other neurons, not H2 receptors. Choice D is incorrect because H2 receptors are not distributed in smooth muscle, endothelium, or presynaptic regions as mentioned in choices A and C.

Correct Answer: C

Rationale: The correct answer is C: L-asparaginase. This enzyme is used in cancer therapy to treat certain types of leukemia by depleting asparagine, an essential amino acid for cancer cell growth. Pepsin (A) is a digestive enzyme, urokinase (B) is involved in fibrinolysis, and lysozyme (D) is an antimicrobial enzyme, none of which are used in cancer therapy.

Correct Answer: B

Rationale: The correct answer is B: Lovastatin (Mevacor). Lovastatin is a statin medication used to lower cholesterol levels. It can cause muscle damage, particularly when used in combination with drugs like erythromycin, which can increase lovastatin levels in the body, leading to an increased risk of muscle-related side effects. Cholestyramine (A) is a bile acid sequestrant used to lower cholesterol, but it does not cause muscle damage. Gemfibrozil (C) and Probucol (D) are also cholesterol-lowering drugs, but they are not known to cause significant muscle damage, especially when combined with erythromycin.

Correct Answer: B

Rationale: The correct answer is B: Paget's disease. Etidronate is a bisphosphonate used to treat Paget's disease, a condition characterized by abnormal bone remodeling leading to bone deformities and pain. It helps inhibit bone resorption and reduce the risk of fractures. A: Malabsorption of vitamin D is not an indication for etidronate, as it does not address the underlying cause of the malabsorption. C: Vitamin D deficiency is not directly treated with etidronate. Supplementation or dietary changes are more appropriate. D: Hypercalciuria is not an indication for etidronate. Etidronate is not used to manage excessive calcium excretion.

Correct Answer: B

Rationale: The correct answer is B, Furosemide (Lasix). Furosemide is a loop diuretic that can cause ototoxicity by affecting the inner ear. It can lead to hearing loss or tinnitus. Acetazolamide (A) is a carbonic anhydrase inhibitor, not associated with ototoxicity. Hydrochlorothiazide (C) and Amiloride (D) are not known to cause ototoxicity.