Purpose: The authors have shown that long-term treatment of cytomegalovirus (CMV) retinitis with 20-μg intravitreal injections of cidofovir (HPMPC) is highly effective but may be associated with iritis and profound hypotony. They evaluated the efficacy and safety of 10-μg intravitreal injections of cidofovir and made comparisons with their findings of 20-μg injections. Methods: The current study was conducted as a nonrandomized consecutive case series at the AIDS Ocular Research Unit of the University of California at San Diego. Twenty-seven eyes of 18 patients were injected with 10 μg intravitreal cidofovir and had complete follow-up. These were compared with another consecutive series of 24 eyes of 17 patients injected with 20 μg of cidofovir. Main Outcome Measures: The main outcome in this study was the incidence of failure to respond to treatment with 10-μg injections. The authors also compared the time to progression of CMV retinitis after the initial intravitreal injections of 10 μg and 20 μg of cidofovir. Secondary outcomes included incidence of iritis and changes in intraocular pressure (IOP) after cidofovir injections. Results: The median time to retinitis progression was 45 days after a single intravitreal injection of 10 μg cidofovir compared with 55 days with the authors' series of 20μg injections. This difference was statistically significant (P = 0.033, log-rank test) and appeared to be due principally to a 26% incidence of primary failure in the 10-μg group (progression ≤ 750 μm within 28 days, P = 0.0017 Wilcoxon test). Progression after a second injection of 10 μg cidofovir was more rapid (32 days, P = 0.037). The incidence of iritis after 10-μg injections was 2.2% compared with 23% with 20-μg injections (P = 0.003, Fisher's exact test, two-tailed). There was less decrease in IOP between the baseline injection and subsequent visits in the 10-μg group. Conclusions: Treatment of CMV retinitis with 10-μg intravitreal cidofovir injection was not as effective as with 20 μg and may allow development of drug resistance, but there were fewer side effects with the 10-μg dose. The drug appears to have a narrow therapeutic index, and other attempts at reducing the side effects while preserving the long-acting effect, such as liposome delivery, may be warranted.
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