A HIV patient with CD4 count of 160 cells/ul presented with fever, cough and shoness of breath for 3 weeks. Chest X ray is shown below. Based on the x ray findings silver staining of the bronchoalveolar lavage was done and shown below. What is drug of choice for the causative organism?

**Core Concept**
The patient's presentation with fever, cough, and shortness of breath, along with a low CD4 count, suggests an opportunistic infection in an immunocompromised individual. The chest X-ray findings and silver staining of the bronchoalveolar lavage suggest the presence of a fungal infection.

**Why the Correct Answer is Right**
The silver staining of the bronchoalveolar lavage shows the presence of Pneumocystis jirovecii, a fungus that primarily affects individuals with severely compromised immune systems, such as those with HIV/AIDS. The drug of choice for treating Pneumocystis jirovecii pneumonia (PCP) is trimethoprim-sulfamethoxazole (TMP-SMX), which acts by inhibiting dihydrofolate reductase and thus preventing the synthesis of tetrahydrofolate, an essential precursor for DNA synthesis.

**Why Each Wrong Option is Incorrect**
* **Option A:** Amphotericin B is an antifungal medication, but it is not the first-line treatment for PCP.
* **Option B:** Fluconazole is an antifungal medication, but it is not effective against Pneumocystis jirovecii.
* **Option D:** Ciprofloxacin is an antibiotic, but it is not effective against Pneumocystis jirovecii.

**Clinical Pearl / High-Yield Fact**
PCP is the most common opportunistic infection in HIV/AIDS patients, and TMP-SMX is the drug of choice for its treatment. However, resistance to TMP-SMX is increasing, and alternative treatments such as trimethoprim-dapsone or atovaquone may be necessary in some cases.

**Correct Answer:** C. Amphotericin B

✓ Correct Answer: D. Cotrimoxazole