Antimicrobials USMLE Step 1 Practice Question
A 34-year-old man with HIV/AIDS and a CD4 count of 45 cells/μL presents to the emergency department with a 5-day history of progressive dyspnea, nonproductive cough, and fever to 38.9°C. His oxygen saturation is 88% on room air, respiratory rate is 24 breaths per minute, and blood pressure is 118/76 mmHg. Chest X-ray demonstrates bilateral diffuse interstitial infiltrates, and serum LDH is elevated at 520 U/L. PCR testing confirms Pneumocystis jirovecii pneumonia. He is initiated on high-dose trimethoprim-sulfamethoxazole and adjunctive dexamethasone given his hypoxemia. On day 4 of therapy, he develops a diffuse maculopapular pruritic rash over his trunk and extremities accompanied by recurrent fever to 38.6°C and mild periorbital edema. Which of the following is the most likely etiology?
Answer choices
- ASecondary infection with Pneumocystis jirovecii in the skin
- BTrimethoprim-sulfamethoxazole hypersensitivity reaction, more common in HIV-infected patientsCorrect answer
- CConcurrent development of acute leukemia from long-term sulfonamide use
- DDexamethasone-induced dermatitis from immunosuppression
- EImmune reconstitution inflammatory syndrome caused by antiretroviral therapy
- FDrug reaction with eosinophilia and systemic symptoms (DRESS) syndrome caused by dexamethasone
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.