**Question:** Treatment of CMV retinitis in AIDS patient is -

A. Ganciclovir
B. Valganciclovir
C. Foscarnet
D. Cidofovir

**Correct Answer:** C. Foscarnet

**Core Concept:**

CMV (Cytomegalovirus) retinitis is a severe vision-threatening ocular complication in immunocompromised patients, particularly those suffering from AIDS (Acquired Immunodeficiency Syndrome). In such cases, antiviral therapy is essential to control the infection and preserve vision. The four options provided are antiviral medications used for treating CMV retinitis.

**Why the Correct Answer is Right:**

Foscarnet (CIDO) is a phosphonoacetic acid analogue that inhibits CMV DNA polymerase, a critical enzyme for viral replication. In patients with AIDS, Foscarnet is a first-line option due to its efficacy, low toxicity compared to other antiviral agents (like Ganciclovir and Cidofovir), and favorable pharmacokinetics.

**Why Each Wrong Option is Incorrect:**

A. Ganciclovir (GCV) is a nucleoside analogue that inhibits CMV DNA polymerase. However, it is less preferred due to its limited oral bioavailability, frequent intravenous administration, and potential nephrotoxicity.

B. Valganciclovir (GCV oral prodrug) is an oral prodrug of Ganciclovir. While it is convenient due to its oral administration, it still has limitations like Ganciclovir, like lower bioavailability, frequent monitoring, and potential nephrotoxicity.

D. Cidofovir is a nucleotide analogue that inhibits CMV DNA polymerase. However, it is associated with high nephrotoxicity, ototoxicity, and reduced efficacy in AIDS patients.

**Clinical Pearl:**

In AIDS patients with CMV retinitis, the choice of antiviral therapy should consider factors like pharmacokinetics, pharmacodynamics, toxicity, and patient convenience. The correct option, Foscarnet (CIDO), addresses these concerns with fewer side effects compared to Ganciclovir, Valganciclovir, and Cidofovir.