Long-acting therapy of viral retinitis with (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine

HPMPC (cidofovir), PMEA (adefovir) and Related Acyclic Nucleoside Phosphonate Analogues: A Review of their Pharmacology and Clinical Potential in the Treatment of Viral Infections

The acyclic nucleoside phosphonate (ANP) analogues are broad-spectrum antiviral agents, with potent and selective antiviral activity in vitro and in vivo. The prototype compounds are: ( S)-1-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC, cidofovir), which is active against a wide variety of DNA viruses; 9-(2-phosphonylmethoxyethyl)adenine (PMEA, adefovir), which is active against retro-, herpes- and hepadnaviruses, and ( R)-9-(2-phosphonylmethoxypropyl) adenine (PMPA), which is active against retro- and hepadnaviruses. The antiviral action of the ANP analogues is based on a specific interaction of the active diphosphorylated metabolite with the viral DNA polymerase. The long intracellular half-life of the active metabolite accounts for the optimal efficacy in infrequent dosing schedules. The potential of HPMPC as a broad-spectrum anti-DNA virus agent, as originally observed in vitro and in vivo, has been confirmed in clinical trials. HPMPC has recently been commercially released in the USA for the treatment of cytomegalovirus retinitis in AIDS patients. In addition, topical systemic HPMPC is being (or will be) explored for use against other herpesviruses (i.e. herpes simplex virus, Epstein-Barr virus, or varicella-zoster virus), by adenoviruses, or by human papilloma- or polyomaviruses. Intravenous HPMPC is associated with dose-dependent nephrotoxicity, that should be counteracted by prehydration and concomitant administration of probenecid, and by the application of an infrequent dosing schedule. The oral prodrug of PMEA, bis(pivaloyloxymethyl)-PMEA, is currently being evaluated in patients infected with human immunodeficiency virus (HIV) or hepatitis B virus. Finally, preclinical data on the efficacy of PMPA in animal retrovirus models point to its potential usefulness against HIV infections, when given either prophylactically or therapeutically in the treatment of established HIV infections.

Cidofovir, a New Agent with Potent Anti-Herpesvirus Activity

Cidofovir is a potent, broad spectrum antiviral agent with activity in vitro and in vivo against cytomegalovirus and other members of the herpesvirus family, as well as certain other DNA viruses. After uptake into cells it is converted enzymatically to cidofovir diphosphate, a structural analogue of deoxycytidine triphosphate, which selectively inhibits viral DNA polymerases relative to host cell polymerases. Cross-resistance to cidofovir is not usually seen with human cytomegalovirus isolates that are foscarnet-resistant, or isolates that are ganciclovir-resistant due to a deficiency in ganciclovir phosphorylation. Cross-resistance is seen, however, with isolates that are ganciclovir resistant due to polymerase mutations. A prolonged elimination phase seen in vivo, correlates with a long intracellular half-life seen in vitro and allows for efficacy in animal models of virus infection with infrequent dosing or prophylaxis. Clinical studies of intravenous cidofovir in cytomegalovirus retinitis in patients with AIDS are claimed to show delay of retinitis progression with maintenance doses given once every 2 weeks.

The antiviral activity and mechanism of action of (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides

One class of compounds that has shown promise as antiviral agents are the (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides, members of the broader class of acyclic nucleoside phosphonates. These HPMP nucleosides are nucleotide analogs and have been shown to be effective inhibitors of a wide range of DNA viruses. Prodrugs of these compounds, which achieve higher levels of the active metabolites within the cell, have an expanded activity spectrum that also includes RNA viruses and retroviruses. Because they are analogs of natural nucleotide substrates, HPMP nucleosides are predicted to target polymerases (DNA polymerases, RNA polymerases and reverse transcriptases), resulting in the inhibition of viral genome replication. Previous work using the replicative enzymes of different viruses including human cytomegalovirus (HCMV) and vaccinia virus DNA polymerases and human immunodeficiency virus type 1 (HIV-1) reverse transcriptase has shown that the activated forms of these compounds are substrates for viral polymerases and that incorporation of these compounds into either the primer strand or the template strand inhibits, but does not necessarily terminate, further nucleic acid synthesis. The activity of these compounds against other viruses that do not encode their own polymerases, like polyoma viruses and papilloma viruses, suggests that host cell DNA polymerases are also targeted. This complex mechanism of action and broad activity spectrum has implications for the development of resistance and host cell genome replication, and suggests these compounds may be effective against other viruses such as influenza virus, respiratory syncytial virus and Dengue virus. This class of nucleotide analogs also points to a potential avenue for the development of newer antivirals.

Reducing chorioretinal viral counts with intravitreal foscarnet injections in a rabbit model of Herpes simplex virus type-1 retinitis

The efficacy of intravitreal foscarnet injections was evaluated in a rabbit model of Herpes simplex virus type-1 (HSV-1) retinitis. In untreated infected animals, viral titration revealed that the optic chiasm, vitreous and chorioretina were positive for HSV-1. On the other hand, foscarnet treatment significantly decreased the viral count in the chorioretina when compared to the untreated group. Immunolocalization of HSV in untreated infected animals clearly showed infected cells in the outer and inner layers of the retina and also in the ciliary body of the eye. Clinical examination by indirect ophthalmoscopy indicated an absence of optic nerve congestion and a lower level of vitritis in foscarnet treated animals compared to the untreated group. It is concluded that intravitreal injections of foscarnet reduced the viral titer in the chorioretina in a rabbit model of HSV-1 retinitis. This route of administration might be valuable for the treatment of CMV retinitis in AIDS patients with sight threatening lesions or intolerance to intravenous anti-CMV drugs.

Cidofovir: a review of its use in cytomegalovirus retinitis in patients with AIDS

Cidofovir is an antiviral nucleotide analogue with significant activity against cytomegalovirus (CMV) and other herpesviruses. The drug is indicated for the treatment of CMV retinitis, a sight-threatening condition, in patients with AIDS. Cidofovir has a long intracellular half-life which allows for a prolonged interval (2 weeks) between maintenance doses. In contrast, other intravenous treatment options for patients with CMV retinitis (i.e. ganciclovir and foscarnet) must be administered on a daily basis. The efficacy of intravenous cidofovir has been demonstrated in patients with AIDS and previously untreated CMV retinitis in multicentre randomised trials, and in a dose-finding study of cidofovir in patients with AIDS and previously treated relapsing CMV retinitis. Clinical trials have been relatively small (n < or = 100 patients) and no studies have been conducted directly comparing intravenous cidofovir with the more established intravenous agents, ganciclovir or foscarnet. Indirect comparisons of clinical trial data suggest that intravenous cidofovir may have similar efficacy to intravenous ganciclovir or foscarnet in delaying progression of CMV retinitis. However, such comparisons must be made with caution because of potential differences in patient populations, data analysis techniques and interobserver variability in the masked assessment of retinal photographs. Nevertheless, intravenous cidofovir offers a less intrusive administration regimen than intravenous ganciclovir or foscarnet because of its prolonged dosage interval. Since therapy is life-long, patients receiving daily intravenous ganciclovir or foscarnet (but not cidofovir) usually require an indwelling central venous catheter and are therefore at increased risk of serious infection. The relatively long dosage interval for cidofovir may also have favourable implications in terms of overall treatment costs and patient quality of life, although specific data are very limited. Potentially irreversible nephrotoxicity is the major treatment-limiting adverse event associated with intravenous cidofovir in patients with AIDS-related CMV retinitis. Anterior uveitis/iritis has been reported frequently with intravenous cidofovir in postmarketing reports and a small number of patients have developed hypotony. Other treatment options for CMV retinitis are also associated with serious adverse events, and selection of pharmacotherapy will depend on a number of factors including retinitis lesion characteristics, patient quality-of-life issues and efficacy and tolerability profiles of available therapies.

CONCLUSION

Although the extent of its use may be limited by its adverse event profile, cidofovir offers a useful addition to the limited number of drugs available for the treatment of CMV retinitis in patients with AIDS.

Intravitreal and plasma cidofovir concentrations after intravitreal and intravenous administration in AIDS patients with cytomegalovirus retinitis

This study was undertaken to evaluate the intravitreal and plasma concentrations of cidofovir (HPMPC) after intravitreal and intravenous administration in AIDS patients with cytomegalovirus retinitis. Cohort series; undiluted vitreous and blood were collected from 9 patients at the time of pars plana vitrectomy. Vitreous samples from 9 eyes of 9 patients and plasma samples from 4 patients were assayed with high-performance liquid chromatography to determine cidofovir levels. The only eye that had a detectable vitreous concentration (673.7 ng/ml) was injected with 20 microg 24 hours prior to the surgery. The remaining samples including plasma were below the detection point of the assay (100 ng/ml) and were injected between 5 and 40 days prior to sampling. The intravitreal concentration of cidofovir in humans is consistent with pharmacokinetics data in laboratory animals, and suggests that the long duration of antiviral effect (1-3 months) in clinical trials is due to a prolonged intracellular half-life in retinal tissue.

Adverse events and autopsy findings after intravitreous cidofovir (HPMPC) therapy in patients with acquired immune deficiency syndrome (AIDS)

OBJECTIVE

The purpose of the study is to evaluate the adverse events and autopsy findings in a series of consecutive 20-microg intravitreous cidofovir injections at a single institution.

DESIGN

The study design was a nonrandomized, consecutive case series.

PARTICIPANTS

Seventy-six patients with acquired immune deficiency syndrome with cytomegalovirus retinitis were studied prospectively. Sixty-three patients had 1 month's follow-up or longer, and this comprised the study group. In addition, histopathologic findings from 18 eyes of 9 patients were studied at autopsy.

INTERVENTION

A total of 296 injections of 20 microg cidofovir were given in 115 eyes. Sixty-three patients who had 246 injections in 93 eyes had 1 month's follow-up or longer for the evaluation of adverse events.

MAIN OUTCOME MEASURES

Postinjection chronic hypotony associated with permanent visual loss, transient hypotony, iritis, and its long-term sequela (posterior synechia and cataract, retinal detachment, extraocular cytomegalovirus involvement) were the outcomes of interest in this study. Additionally, light and electron microscopic studies of human eyes were performed.

RESULTS

The most severe adverse event was postinjection chronic hypotony. This phenomenon was associated with permanent visual loss. This was observed in 1% of the injections and 3% of the eyes of the patients (95% confidence interval, 0%-6%). Transient hypotony associated with mild-to-moderate visual loss developed in 14%, but vision recovered to baseline levels in these eyes subsequently. Analysis showed that transient hypotony in the injected eye could predict postinjection chronic hypotony in the fellow eye (two-tailed Fisher's exact test, P = 0.02). The incidence of iritis was 32%; posterior synechia and cataract were the long-term sequela of the iritis and developed in 19% and 11% of the eyes, respectively. The incidence of retinal detachment was lower (6%). Histopathologic evaluation of the eyes showed mild-to-moderate atrophy of the nonpigmented epithelium of the ciliary body and no other evidence of intraocular toxicity.

CONCLUSIONS

The most serious adverse event was postinjection chronic hypotony, which occurred in 3% of eyes. Episodes of transient hypotony appear to indicate that the fellow eye was predisposed to chronic hypotony. Therefore, it may be prudent to give intravitreous injections at least 2 weeks apart in the fellow eye to evaluate the clinical response of the injected eye.

In search of a selective antiviral chemotherapy

This article describes several approaches to a selective therapy of virus infections: (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU [brivudin]) for the therapy of herpes simplex virus type 1 and varicella-zoster virus infections: (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)cytosine (HPMPC [cidofovir]) for the therapy of various DNA virus (i.e., herpesvirus, adenovirus, papillomavirus, polyomavirus, and poxvirus) infections; 9-(2-phosphonylmethoxyethyl)adenine (PMEA [adefovir]) for the therapy of retrovirus, hepadnavirus, and herpesvirus infections; (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) for the therapy and prophylaxis of retrovirus and hepadnavirus infections; and nonnucleoside reverse transcriptase inhibitors (NNRTIs), such as tetrahydroimidazo[4,5,1-jk][1,4]-benzodiazepin-2(IH)-one and -thione (TIBO), 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT), alpha-anilinophenylacetamide (alpha-APA), and 2',5'bis-O-(tert-butyldimethylsilyl)-3'-spiro-5"-(4"-amino-1",2"-oxat hiole- 2",2"-dioxide)pyrimidine (TSAO) derivatives, and thiocarboxanilides for the treatment of human immunodeficiency virus type 1 (HIV-1) infections. For the clinical use of NNRTIs, some guidelines have been elaborated, such as starting treatment with combinations of different compounds at sufficiently high concentrations to effect a pronounced and sustained suppression of the virus. Despite the diversity of the compounds described here and the different viruses at which they are targeted, they have a number of characteristics in common. As they interact with specific viral proteins, the compounds achieve a selective inhibition of the replication of the virus, which, in turn, should be able to develop resistance to the compounds. However, as has been established for the NNRTIs, the problem of viral resistance may be overcome if the compounds are used from the start at sufficiently high doses, which could be reduced if different compounds are combined. For HIV infections, drug treatment regimens should be aimed at reducing the viral load to such an extent that the risk for progression to AIDS will be minimized, if not avoided entirely. This may result in a real "cure" of the disease but not necessarily of the virus infection, and in this sense, HIV disease may be reduced to a dormant infection, reminiscent of the latent herpesvirus infections. Should virus replication resume after a certain time, the armamentarium of effective anti-HIV and anti-herpesvirus compounds now available, if applied at the appropriate dosage regimens, should make the virus return to its dormant state before it has any chance to damage the host. It is unlikely that this strategy would eradicate the virus and thus "cure" the viral infection, but it definitely qualifies as a cure of the disease.

Intraocular pressure and aqueous humor dynamics in patients with AIDS treated with intravitreal cidofovir (HPMPC) for cytomegalovirus retinitis

PURPOSE

To evaluate the decrease in intraocular pressure associated with cidofovir (1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine dihydrate; HPMPC) intravitreal injections.

METHODS

We followed up 97 eyes of 63 patients with acquired immunodeficiency syndrome (AIDS) who had cytomegalovirus retinitis and had been treated with up to nine 20-microgram intravitreal cidofovir injections. Measurements were taken at baseline, between 2 and 3 weeks, and at 5 to 6 weeks after injections. Anterior chamber fluorophotometry was studied in seven eyes (four patients) before and after injections. Ciliary body anatomy was evaluated in two patients.

RESULTS

After the first intravitreal injection, mean intraocular pressure was 2.2 mm Hg lower than that at baseline at 2 to 3 weeks (P < .001) and 1.3 mm Hg lower than at baseline at 5 to 6 weeks (P = .0025). After the second injection, mean pressure was 2.6 mm Hg lower at 2 to 3 weeks (P = .0013) and 1.5 mm Hg lower at 5 to 6 weeks (P = .043). After subsequent injections, however, the decrease was less than 1 mm Hg, suggesting that a plateau had been reached. Pressure in eyes with anterior uveitis after the first injection was lower than that in eyes without anterior uveitis (P < .0001). The mean rate of aqueous flow decreased from 2.8 to 1.9 microliters per minute 2 to 4 weeks after injection (P < .015). Ultrasound biomicroscopy disclosed that severe hypotony after cidofovir injections is associated with ciliary body atrophy.

CONCLUSIONS

Intraocular pressure decreases after the initial 20-microgram cidofovir intravitreal injection. However, eyes stabilize (pressure plateaus) after three injections. Effects on the ciliary body are the main cause of the decrease after cidofovir injections.

Low-dose intravitreal cidofovir (HPMPC) therapy of cytomegalovirus retinitis in patients with acquired immune deficiency syndrome

PURPOSE

The authors have shown that long-term treatment of cytomegalovirus (CMV) retinitis with 20-microgram 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-microgram intravitreal injections of cidofovir and made comparisons with their findings of 20-microgram 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 micrograms intravitreal cidofovir and had complete follow-up. These were compared with another consecutive series of 24 eyes of 17 patients injected with 20 micrograms of cidofovir.

MAIN OUTCOME MEASURES

The main outcome in this study was the incidence of failure to respond to treatment with 10-microgram injections. The authors also compared the time to progression of CMV retinitis after the initial intravitreal injections of 10 micrograms and 20 micrograms 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 micrograms cidofovir compared with 55 days with the authors' series of 20-microgram 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-microgram group (progression > or = 750 microns within 28 days, P = 0.0017 Wilcoxon test). Progression after a second injection of 10 micrograms cidofovir was more rapid (32 days, P = 0.037). The incidence of iritis after 10-microgram injections was 2.2% compared with 23% with 20-microgram 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-microgram group.

CONCLUSIONS

Treatment of CMV retinitis with 10-microgram intravitreal cidofovir injection was not as effective as with 20 micrograms and may allow development of drug resistance, but there were fewer side effects with the 10-microgram 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.

Herpes simplex: evolving concepts

A large body of molecular biologic research has begun to clarify some basic aspects of viral latency and reactivation. The clinical definition of herpes simplex virus infection is expanding, with the recognition that the disease is largely asymptomatic and that most transmission occurs during periods of asymptomatic viral shedding. With this awareness, serologic diagnosis has become increasingly important. New treatment modalities are now available, and other promising treatments are in development.

Evaluation of Cidofovir (HPMPC, GS-504) against adenovirus type 5 infection in vitro and in a New Zealand rabbit ocular model

The antiviral inhibitory activity of Cidofovir [1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]cytosine dihydrate, HPMPC, GS-504] against adenovirus type 5 (Ad5) in the New Zealand rabbit ocular replication model was evaluated. The 50% inhibitory dose (ID50) of Cidofovir was determined to be 4.7-9.5 micrograms/ml against four adenoviruses (two Ad5, Ad8 and Ad14) by plaque reduction assay in A549 cells. Twenty-four New Zealand rabbits received intrastromal inoculation and topical application of 2 x 10(6) plaque-forming units (PFU) per eye of Ad5 McEwen, a clinical isolate. Cidofovir was administered topically at three different concentrations twice per day, beginning 16 h postinoculation and continuing for 20 consecutive days. The inhibitory effects were determined by measuring suppression of virus replication and by observation of the clinical effects. Compared to the placebo group, the 1% and 0.5% Cidofovir-treated groups showed significantly reduced Ad5 ocular titers, fewer days of viral shedding and less severe subepithelial opacities (P = 0.0001). The 1% Cidofovir group had the lowest humoral antibody titer against adenovirus antigens, but the difference was not significant (P = 0.24). Cidofovir proved to have potent antiviral activity against adenovirus replication and may have great promise for the treatment of adenovirus infection. Further investigation is recommended.

Distribution and metabolism of intravitreal cidofovir and cyclic HPMPC in rabbits

PURPOSE

This study was designed to evaluate the intraocular distribution and metabolism of the antiviral nucleotide analogs cidofovir and cyclic 1-[(S)-3-hydroxy-2-(phosphonomethoxy) propyl]cytosine (HPMPC) in New Zealand white rabbits following intravitreal administration.

METHODS

Male rabbits received either 14C-cidofovir or 14C-cyclic HPMPC by intravitreal injection into both eyes (50 micrograms/eye, 11 microCi/eye). Two animals per group were sacrificed at 24, 48, 72 or 240 h post-dose. Ocular tissues, kidney and liver were oxidized to determine total radioactivity and metabolites were determined by HPLC.

RESULTS

At 24 h post-dose, total radioactivity was 9.96 and 5.18 micrograms-equiv/g for cidofovir and cyclic HPMPC, respectively, in vitreous and 20.9 and 3.54 micrograms-equiv/g, respectively, in retina. Although the initial vitreal clearance was 2-fold faster for the cyclic analog, the estimated terminal elimination half-lives in vitreous (42 hr) and in retina (66-77 hr) were similar for both drugs. By 240 h post-dose, radioactivity in all ocular tissues was approximately ten-fold higher for cidofovir. Radioactivity in vitreous at 240 h after intravitreal dosing with either drug contained cidofovir, cyclic HPMPC and cidofovir-phosphocholine.

CONCLUSIONS

The long retinal half-life observed presumably reflects formation of phosphorylated cidofovir within retinal cells. Cidofovir achieved a ten-fold higher level of phosphorylated drug in retina than cyclic HPMPC: Therefore, intravitreal cidofovir may be expected to suppress progression of retinitis for a longer period than an equivalent intravitreal dose of cyclic HPMPC: The intravitreal half-life of cidofovir was 20-fold longer than that of ganciclovir in the same animal model.

Intravitreal cidofovir (HPMPC) treatment of cytomegalovirus retinitis in patients with acquired immune deficiency syndrome

PURPOSE

The authors previously conducted a pilot, dose-escalating study which suggested that a 20-micrograms dose of intravitreal cidofovir (HPMPC) may be safe and effective in treating cytomegalovirus (CMV) retinitis in humans. The purpose of this series is to expand the authors' prior experience with the 20-micrograms dose of cidofovir as the sole treatment for CMV retinitis in patients with acquired immune deficiency syndrome.

METHODS

The study design was an unmasked consecutive case series trial in a single-center institutional retina referral practice. Eligible patients with acquired immune deficiency syndrome had active CMV retinitis in at least one eye and no evidence of extraocular CMV disease. Patients received a 20-micrograms cidofovir trans pars plana injection and were treated with concomitant oral probenecid. Retreatments were performed for progression of retinitis as determined by serial fundus photographs judged independently by three observers. The primary outcome was time to retinitis progression determined by Kaplan-Meier analysis. Both globes of one patient who had unilateral retinitis were examined pathologically.

RESULTS

There were 37 cidofovir injections in 24 eyes of 17 patients. The median time to retinitis progression after the initial 24 injections was 55 days. The median time to retinitis progression after 8 repeat cidofovir injections was 63 days. There was a significant decrease in intraocular pressure from baseline to both 2 and 4 weeks after injection. A mild to moderate iritis developed in five (20.8%) eyes that responded well to topical medications. Results of histopathologic examination of one treated globe did not show any significant toxic effects.

CONCLUSIONS

This study demonstrates that prolonged arrest of the progression of CMV retinitis may be obtained with a single 20-micrograms cidofovir intravitreal injection. In addition, the effect of the drug appears to be maintained after a second injection. The effects of cidofovir in causing uveitis and a slight lowering of the intraocular pressure require further study.

Phase I/II study of intravitreal cidofovir for the treatment of cytomegalovirus retinitis in patients with the acquired immunodeficiency syndrome

PURPOSE

In this study we evaluated the safety and efficacy of the nucleoside phosphonate analogue intravitreal cidofovir to treat cytomegalovirus retinitis in humans.

METHODS

We conducted a phase I/II unmasked consecutive case series in a single-center institutional referral practice. Eligible patients with the acquired immunodeficiency syndrome had active cytomegalovirus retinitis in at least one eye, despite adequate intravenous therapy with ganciclovir or foscarnet, were intolerant to intravenous therapy, were noncompliant with intravenous therapy, or refused intravenous therapy. In a preliminary safety study (Group 1), ten eyes of nine patients received 14 injections of cidofovir while being treated concurrently with intravenous ganciclovir. In a dose-escalating efficacy study (Group 2), eight eyes of seven patients received 11 injections of cidofovir as sole treatment for cytomegalovirus retinitis. The primary outcome was time to retinitis progression.

RESULTS

In the Group 1 eyes receiving 20 micrograms of cidofovir, the median time to retinitis progression was between 49 and 92 days (mean, 78 days). In Group 2 eyes treated with 20 micrograms cidofovir, the median time to retinitis progression was 64 days (mean, 63 days). Hypotony occurred in the two eyes treated with a 100-micrograms dose of cidofovir and in one of three eyes receiving a 40-micrograms dose. No adverse effects resulted from the remaining 20 cidofovir injections.

CONCLUSIONS

Cidofovir (also known as HPMPC) appears to be safe and effective for the local treatment of cytomegalovirus retinitis, providing a long duration of antiviral effect. These preliminary results indicate that additional studies should be performed to investigate more fully this promising medication.