Okay, let's tackle this question about the drug of choice for cytomegalovirus retinitis in HIV patients. The question is from March 2007, so I need to consider if there have been any updates since then. But since CMV retinitis is a classic topic, the answer is likely still the same.

First, the core concept here is the treatment of opportunistic infections in immunocompromised patients, specifically HIV. Cytomegalovirus (CMV) retinitis is a common complication in advanced HIV/AIDS when CD4 counts are very low. The treatment would involve antiviral agents that target CMV.

The drug of choice for CMV retinitis is usually ganciclovir. Foscarnet and cidofovir are alternatives. Ganciclovir works by inhibiting viral DNA synthesis. It's administered intravenously or as a sustained-release implant in the eye. So the correct answer should be ganciclovir.

Looking at the options, the correct answer is probably option C if the options are A: Acyclovir, B: Zidovudine, C: Ganciclovir, D: Foscarnet. But since the user didn't list the options, I need to make sure. However, the user provided the correct answer as C. Ganciclovir.

Now, why the other options are wrong. Acyclovir is for herpes simplex and varicella-zoster, not effective against CMV. Zidovudine is an antiretroviral, not an antiviral for CMV. Foscarnet is an alternative but not the first-line. Cidofovir is another alternative but less commonly used.

Clinical pearl: Remember that for CMV, ganciclovir is first-line. Also, in HIV patients, starting antiretroviral therapy (ART) is crucial after initiating CMV treatment to prevent immune reconstitution inflammatory syndrome (IRIS). So the key point is ganciclovir as the primary treatment.

**Core Concept**
Cytomegalovirus (CMV) retinitis is an opportunistic infection in immunocompromised patients, particularly those with advanced HIV/AIDS and CD4 counts <50/µL. The treatment targets CMV replication via nucleoside analogs or pyrophosphate analogs. **Why the Correct Answer is Right** **Ganciclovir** is the drug of choice for CMV retinitis. It is a synthetic nucleoside analog that inhibits viral DNA synthesis by phosphorylation into ganciclovir triphosphate, competitively inhibiting viral DNA polymerase. Intravenous ganciclovir or oral valganciclovir (its prodrug) are standard therapies. Sustained-release intraocular implants may also be used. **Why Each Wrong Option is Incorrect** **Option A:** **Acyclovir** is ineffective against CMV; it targets herpes simplex virus (HSV) and varicella-zoster virus (VZV). **Option B:** **Zidovudine** is a nucleoside reverse transcriptase inhibitor (NRTI) used in antiretroviral therapy for HIV, not CMV. **Option D:** **Foscarnet** is a

✓ Correct Answer: B. Ganciclovir