Immunocompromised patient at risk of Pneumocystis jirovecii infection should receive primary prophylaxis with which agent?

• A. Acyclovir
• B. Fluconazole
• C. TMP-SMX for duration of risk
• D. Valacyclovir

Answer: (C)

The key idea is using the most effective preventive therapy to stop Pneumocystis jirovecii pneumonia in someone with suppressed immunity. Trimethoprim-sulfamethoxazole is the standard choice for primary PCP prophylaxis because it reliably prevents Pneumocystis infection across various immunocompromised conditions, such as HIV infection with low CD4 counts and patients on long-term immunosuppressive therapy. Prophylaxis should continue for the duration of risk—renewed immune function or resolution of the immunosuppressive state allows stopping it. If TMP-SMX isn’t possible, alternatives exist (like dapsone, atovaquone, or pentamidine), but they aren’t as consistently effective. The other agents listed target viruses or Candida and do not prevent PCP.