An HIV-infected patient with a CD4 count of 120 cells per microlitre develops progressive exertional dyspnoea and diffuse bilateral interstitial infiltrates. Bronchoalveolar lavage stained with methenamine silver shows crushed ping-pong ball shaped cysts. Which agent is recommended both for treatment and for primary prophylaxis once the CD4 count falls below 200 cells per microlitre?
- A Trimethoprim-sulfamethoxazole ✓
- B Amphotericin B followed by itraconazole
- C Voriconazole
- D Fluconazole
Correct answer: A. Trimethoprim-sulfamethoxazole
Explanation
Pneumocystis jirovecii pneumonia occurs when the CD4 count falls below 200 cells per microlitre. Trimethoprim-sulfamethoxazole is the drug of choice for both treatment of active disease and primary prophylaxis, making it unique among antifungal regimens examined here. Amphotericin B has no role because Pneumocystis lacks ergosterol in its membrane, relying instead on cholesterol, which also explains intrinsic resistance to standard azoles and amphotericin. The cysts appear as collapsed crescentic or ping-pong ball forms on methenamine silver stain.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.