The drug acts by competing with aldosterone for its cytosolic receptors:

Correct Answer: D

Rationale: Step-by-step rationale for why D (Spironolactone) is correct: 1. Spironolactone is an aldosterone receptor antagonist. 2. By competing with aldosterone for its cytosolic receptors, spironolactone inhibits its action. 3. This leads to decreased sodium reabsorption and potassium retention. 4. Spironolactone is used in conditions like heart failure, hypertension, and hyperaldosteronism. Summary of why other choices are incorrect: - A (Acetazolamide): Acts as a carbonic anhydrase inhibitor. - B (Furosemide): Inhibits the Na+/K+/2Cl- cotransporter in the loop of Henle. - C (Hydrochlorothiazide): Inhibits sodium reabsorption in the distal convoluted tubule by blocking the Na+/Cl- cotransporter.

Correct Answer: B

Rationale: The correct answer is B: PAS (para-aminosalicylic acid) because it is a second-line antimycobacterial drug used to treat drug-resistant tuberculosis. Isoniazid and rifampin are first-line agents, and streptomycin is an aminoglycoside antibiotic primarily used for treating bacterial infections, not specifically for mycobacterial infections. PAS is specifically indicated for multidrug-resistant tuberculosis cases, making it a second-line option.

Correct Answer: C

Rationale: The correct answer is C. Mebendazole inhibits microtubule synthesis in helminths, leading to irreversible impairment of glucose uptake. This disrupts the helminths' ability to maintain their structure and energy production, ultimately causing their death. A, B, and D are incorrect as mebendazole does not work by inhibiting oxidative phosphorylation, increasing cell membrane permeability for calcium, or blocking acetylcholine transmission. These mechanisms are not associated with mebendazole's mode of action.

Correct Answer: D

Rationale: The correct answer is D: Anastrozole. Anastrozole is an aromatase inhibitor that works by blocking the enzyme aromatase, which is responsible for converting androgens into estrogen. By inhibiting estrogen production, Anastrozole effectively reduces estrogen levels in the body. Leuprolide (A) is a gonadotropin-releasing hormone agonist that suppresses estrogen production indirectly. Tamoxifen (B) is a selective estrogen receptor modulator that blocks estrogen receptors. Flutamide (C) is an antiandrogen that blocks the effects of androgens, not estrogen.

Correct Answer: A

Rationale: The correct answer is A: Lovastatin. Lovastatin is a statin medication that can increase the risk of bleeding, which would be problematic for a patient with hemophilia and external hemorrhoids. Statins can interfere with the liver's production of clotting factors, exacerbating bleeding issues in hemophiliac patients. Choice B: Cholestyramine is a bile acid sequestrant used to lower cholesterol levels and is not directly contraindicated in hemophilia or hemorrhoids. Choice C: Ezetimibe is a cholesterol absorption inhibitor and does not directly affect bleeding risk in hemophiliac patients with hemorrhoids. Choice D: Niacin is a B vitamin that can cause flushing and itching, but it does not have a direct contraindication in patients with hemophilia and external hemorrhoids.