CMV Colitis in HIV/AIDS

A 36-year-old man with poorly controlled HIV (CD4 28 cells/µL, not on ART) presents with 2 weeks of crampy abdominal pain, profuse watery diarrhea progressing to bloody diarrhea, fever, and 6 kg weight loss. Colonoscopy reveals deep, well-demarcated longitudinal serpiginous ulcers in the descending colon with patchy yellow-white pseudomembranes and submucosal hemorrhage. Biopsies from the **ulcer edges** show enlarged endothelial and stromal cells with characteristic "owl-eye" intranuclear inclusions surrounded by a clear halo, plus cytoplasmic basophilic inclusions. CMV PCR is positive. The diagnosis is **Cytomegalovirus colitis** as marked in position **B** of the diagram. What is the most appropriate initial management?