Although therapy with foscarnet or ganciclovir halts retinitis progression in 90 percent of patients treated, relapses are common and may accelerate due to development of drug resistance, deteriorating immune function, or other factors. Treatment strategies currently being investigated include switching patients from one drug to the other or combining the two drugs.

Patients are randomized to receive foscarnet, ganciclovir, or a combination of the two drugs (administered sequentially). Initially, patients undergo single or multiple cycles of induction therapy for 14 days followed by maintenance therapy. Patients in whom the retinitis continues to progress or who are intolerant of the initial treatment switch to the alternative drug for further cycles of induction and maintenance. Patients on the combination arm in whom retinitis continues to progress are given further cycles of the combination at an increased dose, or, if one drug is causing toxicity, are given further cycles with the alternative drug. Patients are followed monthly for 6 months and then every 3 months thereafter.