This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Viral Drugs, Subject name: Pharmacology
Which of the following is drug of choice for CMV retinitis? 
Select and explain. 
A. Acyclovir, B. Tenofovir, C. Ganciclovir, D. Abacavir
C: Ganciclovir
Answer: C: Ganciclovir 
Explanation: Doc for CMV retinitis - Ganciclovir Other drugs used - Foscarnet, cidofovir Herpes simplex virus (HSV), Varicella zoster virus (VZV) - Acyclovir Anti HIV drugs - Tenofovir, Abacavir Ganciclovir: Activated intracellularly by virus specific thymidine kinase Due to poor oral absorption, bioavailability of ganciclovir is low (<10%) It's prodrug valganciclovir ,which is better absorbed orally, has replaced it for oral therapy Systemic S/E: Bone marrow depression Rash ,fever,vomiting Neuro psychiatric disturbances