The drug acts by competitively blocking the Na+/K+/2Cl- cotransporter:

Correct Answer: A

Rationale: Loop diuretics act by competitively blocking the Na+/K+/2Cl- cotransporter in the thick ascending limb of the loop of Henle. By inhibiting this transporter, loop diuretics prevent reabsorption of sodium, potassium, and chloride ions, leading to increased urine output. Thiazide diuretics work in the distal convoluted tubule by blocking the Na+/Cl- cotransporter. Potassium-sparing diuretics act on the collecting duct or distal tubule to inhibit sodium reabsorption and potassium secretion. Carbonic anhydrase inhibitors work in the proximal convoluted tubule by inhibiting the enzyme carbonic anhydrase, which reduces bicarbonate reabsorption. Therefore, the correct answer is A because loop diuretics specifically target the Na+/K+/2Cl- cotransporter in the loop of Henle.

Correct Answer: A

Rationale: The correct answer is A: Pyrazinamide. Pyrazinamide is not a bactericidal drug but rather a bacteriostatic drug. It inhibits the growth of mycobacteria rather than directly killing them. Streptomycin, Rifampin, and Isoniazid are all bactericidal drugs that directly kill mycobacteria. Streptomycin disrupts protein synthesis, Rifampin inhibits RNA synthesis, and Isoniazid inhibits mycolic acid synthesis in mycobacteria, leading to their death. Therefore, Pyrazinamide is the only drug among the options that does not have a bactericidal effect.

Correct Answer: A

Rationale: The correct answer is A: Foscarnet. Foscarnet is a derivative of pyrophosphate as it contains a phosphonoformic acid group that mimics pyrophosphate. This structural similarity allows foscarnet to inhibit viral DNA polymerase by binding to the pyrophosphate-binding site. Zidovudine (B), Vidarabine (C), and Acyclovir (D) are not derivatives of pyrophosphate and act through different mechanisms to inhibit viral replication. Zidovudine is a nucleoside reverse transcriptase inhibitor, Vidarabine is a nucleoside analog, and Acyclovir is a guanosine analog.

Correct Answer: B

Rationale: The correct answer is B: Triamterene. Triamterene is a potassium-sparing diuretic that helps prevent new stone production by inhibiting sodium reabsorption in the kidneys, reducing the risk of stone formation. Mannitol (A) is an osmotic diuretic used for specific medical conditions, not for preventing stone formation. Conivaptan (C) is a vasopressin receptor antagonist primarily used for hyponatremia, not for preventing stone formation. Acetazolamide (D) is a carbonic anhydrase inhibitor that can help with certain types of kidney stones but is not typically used for preventing new stone production.

Correct Answer: A

Rationale: Verapamil is the correct choice as it is a calcium channel blocker that can help prevent cerebral vasospasm, reducing the risk of delayed cerebral ischemia in subarachnoid hemorrhage. Verapamil works by dilating blood vessels, improving blood flow to the brain. Isosorbide mononitrate (B) is a nitrate used for angina, not specifically for cerebral ischemia. Propranolol (C) is a beta-blocker and Dobutamine (D) is a positive inotrope that are not directly indicated for preventing cerebral ischemia in this context.