The antibiotic used for treating Pneumocystis jiroveci pneumonia (PCP) is?

The antibiotic trimethoprim-sulfamethoxazole is the first-line treatment for Pneumocystis jiroveci pneumonia (PCP). This combination works synergistically to inhibit bacterial folic acid synthesis, which is critical for the growth and replication of the organism responsible for PCP. Trimethoprim inhibits dihydrofolate reductase, while sulfamethoxazole blocks the enzyme dihydropteroate synthase, together disrupting the folate pathway essential for DNA synthesis.

PCP is particularly a concern in immunocompromised individuals, such as those with HIV/AIDS, and prompt treatment with trimethoprim-sulfamethoxazole is crucial in managing the infection effectively. Other treatments, like atovaquone and pentamidine, may be used in specific cases, but trimethoprim-sulfamethoxazole remains the standard choice due to its proven efficacy and the broad spectrum of coverage it offers.

The other options do not have the same effectiveness against Pneumocystis jiroveci. Azithromycin, while effective against various bacterial infections, does not target the specific metabolic pathways of Pneumocystis. Ciprofloxacin, a fluoroquinolone, is mainly used