Snapshot A 33-year-old man presents to the emergency department with new-onset vision blurriness with "flashing lights." His symptoms began approximately 4 days prior to presentation and have progressively worsened. He occasionally sees floaters, and his symptoms affect both eyes but are more severe on the left eye. He has a past medical history of HIV infection and reports to not taking his medication for the past year. Ophthalmology was consulted and performed a dilated ocular exam. Indirect ophthalmoscopy demonstrated 1-2 yellow-white foci of disease in a perivascular distribution accompanied by retinal hemorrhage in a "brush fire" pattern. His CD4+ count is 39/uL. She is started on cidofovir and antiretroviral therapy. (Cytomegalovirus retinitis) Introduction Mechanism of action acts as a nucleotide analog, by which it competitively inhibits nucleotide (deoxycytidine triphosphate) incorporation into viral DNA by viral DNA polymerase no viral kinase activity is required for activation of cidofovir (in contrast to ganciclovir) however, host cell kinases still required for activation Mechanism of resistance altered viral DNA polymerase Clinical use cytomegalovirus (CMV) infection CMV retinitis acyclovir-resistant herpes simplex virus infections Adverse effects dose-dependent nephrotoxicity monitored by checking serum creatinine and urine protein nephrotoxicity can be reduced with hydration and probenecid ophthalmologic disturbances due to toxicity to ciliary body iritis uveitis decreased intraocular pressure possible vision loss