Drug of choice for prophylaxis of Pneumocystis jiroveci pneumonia in immunocompromised patients is:
**Core Concept**
Pneumocystis jiroveci pneumonia (PCP) is an opportunistic infection that affects immunocompromised patients, such as those with HIV/AIDS or undergoing chemotherapy. The prophylaxis of PCP requires the use of antimicrobial agents that can prevent the growth of this pathogen.
**Why the Correct Answer is Right**
The drug of choice for prophylaxis of PCP is trimethoprim-sulfamethoxazole (TMP-SMX). TMP-SMX acts by inhibiting dihydrofolate reductase, an enzyme necessary for the synthesis of tetrahydrofolate, which is required for the growth and replication of P. jiroveci. This combination therapy is effective in preventing PCP in immunocompromised patients and is considered the first-line treatment for PCP prophylaxis.
**Why Each Wrong Option is Incorrect**
**Option A:** Pentamidine is an alternative option for PCP prophylaxis, but it is not the preferred choice due to its potential side effects and the development of resistance.
**Option B:** Cotrimoxazole-resistant P. jiroveci strains have been reported, but this is not a common issue with TMP-SMX prophylaxis.
**Option C:** Atovaquone is another option for PCP prophylaxis, but it is not as effective as TMP-SMX and is typically reserved for patients who cannot tolerate TMP-SMX.
**Clinical Pearl / High-Yield Fact**
It is essential to note that PCP prophylaxis should be initiated in immunocompromised patients with a CD4 count below 200 cells/μL or those with a history of PCP.
**Correct Answer: C. Atovaquone.