Design and Patients
Nine patients with clinically resistant cytomegalovirus retinitis who had shown progression of retinitis despite extended intravenous induction single drug therapy or alternating therapy with induction doses of ganciclovir or foscarnet at 6 weeks were subsequently treated with a combination of ganciclovir and foscarnet. The dosing regimen for induction combination therapy was ganciclovir at 5 mg/kg every 12 hours and foscarnet at 60 mg/kg every 8 hours. Maintenance combination therapy was ganciclovir at 5 mg/kg every 12 to 24 hours and foscarnet at 90 to 120 mg/kg every day. Patients were observed closely for signs of a toxic effect or intolerance to the drug regimen.

Results
All patients exhibited a favorable response to combination therapy, with complete healing of retinitis in 12 of 14 eyes and partial healing of retinitis with decreased border activity and a cessation of border advancement in two of 14 eyes. Two of the nine patients stopped receiving combination therapy before completion of the study owing to their dissatisfaction with the time commitment. The regimen was otherwise well tolerated, with no significant medical toxic effects attributable to the drugs requiring cessation of therapy.

Conclusions
Combination anticytomegalovirus therapy should be considered in those patients who have shown a poor clinical response to sustained single-drug induction therapy and alternating drug therapy. As survival time for patients with cytomegalovirus retinitis continues to improve, clinical resistance may become more common. Further work to delineate the optimal dosing and indications for combination therapy will be important.