Which of the following drugs is penicillinase resistant:

Correct Answer: A

Rationale: The correct answer is A: Oxacillin. Oxacillin is penicillinase-resistant due to its side chain that protects it from penicillinase enzymes. This side chain confers resistance against beta-lactamase enzymes produced by certain bacteria. On the other hand, choices B, C, and D are not penicillinase-resistant. Amoxicillin and Penicillin G are susceptible to penicillinase enzymes, while Bicillin-5 is a combination of penicillin G and penicillinase-sensitive benzathine penicillin. Thus, Oxacillin is the only penicillinase-resistant drug among the options provided.

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.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.