<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 45-year-old man comes to the emergency department with fever, nonproductive cough, and difficulty breathing. Three years ago, he underwent lung transplantation. A CT scan of the chest shows diffuse bilateral ground-glass opacities. Pathologic examination of a transbronchial lung biopsy specimen shows several large cells containing intranuclear inclusions with a clear halo. Treatment with ganciclovir fails to improve his symptoms. He is subsequently treated successfully with another medication. This drug does not require activation by viral kinases and also has known in-vitro activity against HIV and HBV. The patient was most likely treated with which of the following drugs?? A: Foscarnet, B: Lamivudine, C: Elvitegravir, D: Zanamivir, E: Acyclovir,  <response>: This is a clinical vignette describing a 45-year-old male lung transplant recipient who presents with fever, cough, and dyspnea. He has ground glass opacities on CT chest and transbronchial biopsy shows intranuclear inclusions suggestive of viral infection. He fails ganciclovir but improves with another antiviral medication that does not require viral activation and has activity against HIV and HBV. Based on the clinical presentation of viral pneumonia in an immunocompromised host and the pathologic findings of intranuclear inclusions, this is most likely cytomegalovirus CMV pneumonia. Ganciclovir is first-line for CMV but the patient failed this medication. The medication that ultimately worked does not require viral activation and has activity against other viruses like HIV and HBV. This narrows down the options to foscarnet or cidofovir. However, cidofovir requires activation by viral kinases. Therefore, the patient was most likely treated successfully with foscarnet.A: Foscarnet 