This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti Microbial, Subject name: Pharmacology
[{'content': 'Drug not used in CMV retinitis: \nSelect and explain. \nA. Acyclovir, B. Foscarnet, C. Ganciclovir, D. Cidofovir', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref: Goodman & Gillman\'s 13th ed. P 1106-7* Acyclovir\'s clinical use is limited to herpes viruses. Acyclovir is most active against HSV-1.* Approximately half as active against HSV-2, and a tenth as potent against VZV and EBV.* Book states: "Acyclovir is ineffective therapeutically in established CMV infections, but ganciclovir is effective for CMV prophylaxis in immunocompromised patients* EBV-related oral hairy leukoplakia may improve with acyclovir.* Drugs which can be used in treatment of CMV retinitis are cidofovir, ganciclovir, foscarnet, valaciclovir.* DOC for CMV retinitis: Ganciclovir* Fomivirsen is active against CMV strains resistant to ganciclovir, foscarnet, and cidofovir. Fomivirsen is given by intravitreal injection unresponsive to other therapies.', 'role': 'assistant'}]