Pneumocystis pneumonia treatment — DTM&H MCQ

Correct answer: C — High-dose co-trimoxazole

High-dose co-trimoxazole (option E) is correct because trimethoprim-sulfamethoxazole is the first-line treatment of choice for Pneumocystis jirovecii pneumonia (PCP) of any severity in HIV-positive patients, as recommended by current UK HIV guidance. The vignette gives the classic triad of an HIV-positive patient with a low CD4 count, subacute dry cough, exertional hypoxia and diffuse interstitial infiltrates, with the diagnosis confirmed by induced sputum microscopy, which is diagnostic and mandates specific anti-Pneumocystis therapy rather than empirical antibacterial cover. High-dose co-trimoxazole is given intravenously or orally depending on severity, and adjunctive corticosteroids are added when there is significant hypoxaemia (arterial oxygen tension under 9.3 kPa) to reduce inflammatory deterioration during treatment. No other agent listed has activity against this fungal-like organism. Why the other options are wrong: E. Praziquantel: this is an anthelmintic used for schistosomiasis and other trematode or cestode infections; it has no activity against Pneumocystis, which is not a helminth. D. Fluconazole: this triazole antifungal targets ergosterol synthesis in true fungi such as Candida and Cryptococcus, but Pneumocystis lacks ergosterol in the same pathway and is intrinsically resistant to azoles. A. Amoxicillin: this beta-lactam antibiotic covers typical bacterial pathogens and would be relevant for community-acquired bacterial pneumonia, but it has no effect on Pneumocystis jirovecii, which is unaffected by cell-wall-active antibiotics. B. Artesunate: this is an antimalarial used for severe Plasmodium falciparum infection and has no role whatsoever in a confirmed Pneumocystis pneumonia. Key point: in HIV-associated PCP confirmed on sputum or lavage, high-dose co-trimoxazole is first-line therapy regardless of severity, with corticosteroids reserved for those with significant hypoxaemia.

Reference: British HIV Association (BHIVA) Guidelines on the management of opportunistic infection in people living with HIV: the clinical management of pulmonary opportunistic infections (2024), Section 5.5.2, First-line regimens for treatment of PCP; https://onlinelibrary.wiley.com/doi/full/10.1111/hiv.13637