The drug acts in the distal convoluted tubule:

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: Nitrofurantoin is the correct answer because it is a nitrofurane derivative with antibacterial properties, commonly used to treat urinary tract infections. Trimethoprim, Ciprofloxacin, and Nystatin are not nitrofurane derivatives and have different mechanisms of action, making them ineffective for this purpose.

Correct Answer: B

Rationale: The correct answer is B: Rimantadine. Rimantadine inhibits the uncoating of viral RNA by preventing the release of viral RNA into the host cell. This disrupts the replication process of the virus. Vidarabine (A) inhibits viral DNA polymerase, not viral RNA uncoating. Acyclovir (C) inhibits viral DNA polymerase as well. Didanozine (D) is an antiretroviral drug used in HIV treatment, not for inhibiting viral RNA uncoating.

Correct Answer: C

Rationale: The correct answer is C: Increased capacitance of systemic veins. Nitrates cause vasodilation, leading to increased venous capacitance, reducing preload and myocardial oxygen demand. Decreased ejection time (A) and decreased arterial pressure (D) are actually beneficial effects of nitrates, as they reduce cardiac workload. Increased cardiac rate (B) is not a common adverse effect of nitrates in the treatment of exertional angina.

Correct Answer: A

Rationale: The correct answer is A: Inhibition of phosphodiesterase. Milrinone is a phosphodiesterase inhibitor, which increases cAMP levels, leading to enhanced cardiac contractility. This occurs through the inhibition of the breakdown of cAMP, resulting in increased intracellular calcium levels and improved myocardial function. Choice B is incorrect because while protein kinase can increase cytoplasmic Ca2+, it is not the primary mechanism of milrinone's positive inotropic action. Choice C is incorrect as milrinone does not directly inhibit the Ca2+/Na+ exchanger. Choice D is incorrect as activation of phospholipase A2 is not the mechanism through which milrinone exerts its positive inotropic effects.