Innovative Famciclovir Eye Drop Formulations for Herpes Zoster Infections.

Purpose: Herpes zoster ophthalmicus, a manifestation of the varicella-zoster virus in the eye, presents significant clinical challenges. As there is no direct ocular treatment for this infection, new therapeutic options should be studied. Famciclovir, a widely used antiviral drug for herpes zoster, offers higher bioavailability than acyclovir (a common herpes zoster treatment). However, this drug is currently limited to oral dosage forms, which are associated with inherent limitations such as variable absorption or gastrointestinal side effects. This study aimed to formulate new famciclovir eye drops for controlled drug release and targeted delivery to the cornea and sclera.

Method: Eye drop formulations containing various polymers (polyvinyl alcohol, hydroxypropyl methyl cellulose and chitosan) were developed and evaluated for physicochemical properties, irritation index and stability. The best performing formulation was used in ex-vivo diffusion and retention studies with rabbit cornea and sclera. The results were analyzed with a new HPLC validation method.

Results: The formulation with polyvinyl alcohol exhibited superior properties regarding transparency, turbidity and absence of bubbles. It maintained a physiological pH over time and had an appropriate viscosity of 19.97 ± 0.25 mPa^.s. Non-irritancy was confirmed by the HET-CAM test, and the formulation was stable at room temperature (25 °C), fridge (4 °C) and freezer (-80 °C). Ex- vivo diffusion studies revealed higher diffusion through the sclera compared to the cornea, with greater drug accumulation in sclera.

Conclusions: These findings suggest that famciclovir eye drops may offer a viable treatment for ocular herpes zoster infections. Famciclovir also diffuses and retains in targeted membranes, possibly enhancing its therapeutic effects.