INCIDENCE OF FOSCARNET RESISTANCE AND CIDOFOVIR RESISTANCE IN PATIENTS TREATED FOR CYTOMEGALOVIRUS RETINITIS

Cytomegalovirus (CMV) retinitis is a common opportunistic infection in patients with AIDS, With long-term therapy for CMV retinitis, resista nt CMV may develop. In a prospective study of 122 patients with CMV re tinitis, 2.4 and 0.8% of patients had foscarnet-resistant blood cultur e isolates (50% inhibitory concentration [IC50], >400 mu M) and urine culture isolates, respectively, at diagnosis of CMV retinitis prior to treatment, whereas 4.1 and 6.6% had cidofovir-resistant (IC50, >2 mu M) blood and urine culture isolates, respectively. Patients were treat ed according to best medical judgement. Of 44 foscarnet-treated patien ts, 26% had a resistant blood or urine culture isolate by 6 months of treatment and 37% had a resistant isolate by 9 months; of 13 cidofovir -treated patients, 29% had a resistant blood or urine culture isolate by 3 months of therapy. The probabilities of developing foscarnet resi stance while on foscarnet and developing cidofovir resistance while on cidofovir were not significantly different from that for developing g anciclovir resistance while on ganciclovir (odds ratios, 1.87 [P = 0.1 9] and 2.28 [P = 0.15], respectively).