In an HIV-infected patient with CD4 count 110 cells/microL and a sulfa allergy, which antimicrobial should be used prophylactically for Pneumocystis jirovecii pneumonia?

• A. Azithromycin 1,200 mg once weekly
• B. Dapsone 100 mg daily
• C. Rifabutin 300 mg daily
• D. Trimethoprim-sulfamethoxazole DS daily

Answer: (B)

When preventing Pneumocystis jirovecii pneumonia in an HIV patient, prophylaxis is indicated once the CD4 count falls below 200. The usual first-line drug is trimethoprim-sulfamethoxazole, but this patient has a sulfa allergy, so a non-sulfa alternative is needed. Dapsone, given as 100 mg daily, provides effective PCP prophylaxis and is a well-established option in this setting. It works through inhibition of folate synthesis like the sulfa component, but without using a sulfa drug, making it suitable for those with sulfa allergies.

Before starting dapsone, it’s important to check for G6PD deficiency because dapsone can cause hemolysis and methemoglobinemia in that condition; ongoing monitoring of the blood count is also advised. Other options listed, such as azithromycin or rifabutin, are used for Pneumocystis prophylaxis only indirectly or for different opportunistic infections (e.g., MAC) and are not appropriate PCP prophylaxis.