A new efficacious antiviral therapy with a favorable therapeutic index is needed for acute infections caused by human adenovirus (Ad5). Ad5 is a moderately large (~90 nm in diameter), very stable, double-stranded DNA virus. The Ad5 family comprises at least 51 serotypes, subdivided into A to F species.
1 Although infections are typically self-limiting, adenoviruses are extraordinarily infectious and are associated with community and nosocomial epidemics, especially conjunctivitis, in the United States and worldwide.
2–4 Ad5 infections often lead to visual damage. Such outbreaks can be costly because of lost productivity; severe epidemics have necessitated the closing of facilities such as hospitals, schools, and nurseries.
5 Epidemic adenoviral keratoconjunctivitis (EKC) typically is a self-limiting disease that resolves in approximately 2 weeks. However, given the disproportionate morbidity and potential economic impact associated with an outbreak of EKC, a therapeutic agent that reduces clinical symptoms of EKC and minimizes shedding of infectious virus would be desirable. Currently, no specific antiadenoviral drug is available for the treatment of ocular adenoviral infection. Although numerous therapeutic agents have been assessed for adenoviral keratoconjunctivitis, none of the candidate drugs has been approved for the treatment of adenoviral eye disease by the U.S. Food and Drug Administration (FDA).
6–8 However, the clinical trials websites for Alcon Research
8 and Foresight Biotherapeutics
9 note ongoing clinical trials for ocular antiadenoviral agents.
Various antiviral agents effective against DNA viruses have been evaluated as treatments for EKC.
10,11 Many reports document the inhibition of Ad5 replication in vitro by cidofovir
7,12,13 and another similar drug, the anti-HIV nucleoside reverse transcriptase inhibitor (NRTI) zalcitabine, or 2′,3′-dideoxycytidine (ddC).
14,15 Cidofovir has shown some limited efficacy in clinical trials, as indicated by a lower frequency of severe corneal opacities in individuals with adenoviral keratoconjunctivitis, although dose-dependent toxicity has been observed.
16 Cidofovir has also shown success in the treatment of Ad5 eye infection in the New Zealand White (NZW) rabbit ocular model.
17 Two anti-HIV NRTIs, ddC and stavudine (Zerit, or d4T; Bristol-Meyers Squibb, New York, NY), showed significant antiadenoviral activity in vitro.
18 The FDA has approved ddC for the treatment of HIV (Hivid; Roche Laboratories, Indianapolis, IN), but Roche discontinued the production and distribution of ddC in December 2006. A recent study evaluated ddC+cidofovir as a standard against a panel of ocular adenovirus serotypes and in a rabbit Ad5 replication ocular model and demonstrated potent antiadenovirus activity in vitro and in vivo.
19 A recent study of the adverse effects of the potential antiadenoviral agent cidofovir and the anti-HIV agents ddC and d4T in uninfected eyes and ocular adnexa of healthy female Japanese albino rabbits reported some toxicity associated mainly with cidofovir.
20 In a separate study, ddC was more cytotoxic than cidofovir.
19 Thus, the toxicity in these animal studies reduces the suitability of either cidofovir or ddC for use as an ocular therapeutic agent for EKC in humans.
Case studies on the nucleoside analogue ribavirin for systemic adenoviral infection have yielded inconsistent results,
21,22 because among species A to F, only C serotypes are sensitive to ribavirin in vitro.
23Current approaches to treatment of EKC include the use of artificial tears and cold compresses to reduce patient discomfort and topical regimens including antibiotics and steroids with varied outcomes.
24 A small, prospective, open-label, single-armed clinical trial of dexamethasone 0.1%/povidone-iodine 0.4% (FST-100) administration in humans with symptoms of acute conjunctivitis who tested positive for adenoviral antigen was therapeutically successful.
25 This proprietary mixture containing a steroid and antiseptic is promising as a suitable therapeutic agent for the treatment of EKC. Dexamethasone is a potent, well-tolerated steroid
26,27 that has been used extensively as a topical ophthalmic agent alone and in combination regimens.
25,28–30 Povidone-iodine is an antiseptic extensively used in preparation for general surgery, ophthalmic purposes, and laboratory disinfection.
31–37 Dilute povidone-iodine solutions inhibit numerous viruses, bacteria, fungi, and some other parasites.
38,39 Jiang et al.
40 have reported the safety and feasibility of the use of 0.5% or 1.0% concentrations of povidone-iodine on the rabbit cornea by administration through conjunctival sac instillation for preoperative antisepsis. In this study, FST-100 was compared for its therapeutic efficacy against 0.5% cidofovir with two controls, tobramycin/dexamethasone (Tobradex; Alcon Laboratories, Fort Worth, TX) and balanced salt solution (BSS; Alcon Laboratories), in a rabbit model of adenoviral keratoconjunctivitis.