Liposome-Encapsulated (S)-1-(3-Hydroxy-2-Phosphonylmethoxypropyl)cytosine for Long-Acting Therapy of Viral Retinitis

The effect of liposome-encapsulated (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC; cidofovir) was evaluated as prophylaxis in a rabbit model of experimentally induced retinitis caused by preretinal inoculation of herpes simplex virus type 1 (HSV-1). Cidofovir (100 micrograms) in liposomes (0.1 mL) was injected intravitreally 10-120 days before retinal inoculation with HSV-1. Twenty-two of 26 eyes pretreated with liposome-encapsulated cidofovir 10-60 days before HSV-1 inoculation were protected from experimentally induced retinitis, and 2 of 5 eyes pretreated 120 days before inoculation were protected. Intravitreal levels of cidofovir were low (0.7 microgram/mL) but detectable 120 days after injection. One 100-micrograms intravitreal injection of liposome-encapsulated cidofovir appears to have a remarkably potent and prolonged (up to 4 months) antiviral effect in this experimental model of HSV-1 retinitis. Since HPMPC is even more potent against cytomegalovirus than HSV-1, liposome-encapsulated cidofovir may prove to be effective local therapy for AIDS patients with cytomegalovirus retinitis.