Which medication is recommended for prophylaxis against Pneumocystis jirovecii in AIDS patients?

Trimethoprim-sulfamethoxazole is the recommended medication for prophylaxis against Pneumocystis jirovecii pneumonia (PCP) in patients with AIDS, especially when their CD4 count falls below 200 cells/mm³. PCP is a significant opportunistic infection associated with AIDS, and the use of this combination antibiotic has been shown to be effective in reducing the incidence of PCP among immunocompromised patients.

The mechanism of action involves the inhibiting of bacterial folic acid synthesis, which disrupts the growth of the organism responsible for PCP. This treatment is particularly important in the setting of AIDS and is a standard part of preventive care for patients with elevated risk.

Amphotericin B, while a potent antifungal, is not indicated for PCP prevention. Azithromycin is primarily used for different types of infections and does not have a role in PCP prophylaxis. Vancomycin is an antibiotic effective against certain gram-positive bacteria and is unrelated to Pneumocystis jirovecii. Thus, Trimethoprim-sulfamethoxazole is the most appropriate choice in this clinical scenario.