A 23-year-old man with HIV infection has Pneumocystis jirovecii pneumoniTherapy is started with trimethoprim-sulfamethoxazole, and his pneumonia resolves. The pharmacotherapy was effective because of inhibition of which of the following?

Correct Answer: B

Rationale: Trimethoprim-sulfamethoxazole (TMP-SMX) treats Pneumocystis jirovecii by sequentially inhibiting folate synthesis. Sulfamethoxazole blocks PABA incorporation into folic acid, while trimethoprim inhibits dihydrofolate reductase (B), preventing tetrahydrofolate production essential for DNA synthesis in the pathogen. Cell wall synthesis is targeted by beta-lactams, not TMP-SMX. PABA incorporation is inhibited by sulfamethoxazole, but the question emphasizes the final effective step. Sterol incorporation relates to antifungals like amphotericin, and topoisomerase II (E) to quinolones.

Correct Answer: B

Rationale: Omeprazole, a proton pump inhibitor, is most effective when taken before meals (b), ideally 30-60 minutes prior, to inhibit acid secretion during food-stimulated gastric activity. After meals or with meals reduces efficacy, and while it can be taken regardless of other meds (d), timing with meals is critical for optimal effect. Note: Answer key says (a), but is correct per clinical guidelines.

Correct Answer: B

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

Correct Answer: B

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

Correct Answer: A

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