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: The correct answer is C) Grapefruit juice. Grapefruit juice contains compounds that inhibit the enzyme CYP3A4 in the intestine, which is responsible for metabolizing nifedipine. When this enzyme is inhibited, more of the drug is absorbed into the bloodstream, leading to a higher concentration of nifedipine, thus enhancing its antihypertensive effect. Option A) Concomitant use of antacids: Antacids typically do not have a significant interaction with nifedipine that would lead to a rapid enhancement of its antihypertensive effect. Option B) Foods containing tyramine: Tyramine-containing foods are known to interact with certain classes of drugs, like MAOIs, but not with nifedipine in a way that would rapidly enhance its antihypertensive effect. Option D) Induction of drug metabolism: Inducing drug metabolism would typically lead to a decrease in drug levels, not a rapid enhancement of its effects as seen in the scenario described. Educational context: Understanding drug interactions is crucial in clinical practice to ensure patient safety and optimal therapeutic outcomes. Healthcare providers need to be aware of how different substances can affect drug metabolism and efficacy to make informed decisions when managing patients on multiple medications. This case highlights the importance of considering dietary factors, like grapefruit juice, in medication management for individuals on nifedipine therapy.