Chemical stability of new acyclovir analogues with peptidomimetics

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.

Calculation procedures and HPLC method for analysis of the lipophilicity of acyclovir esters

Acyclovir (ACV) belongs to a class of drugs with low bioavailability. Selected ACV esters including acetyl (Ac-), isobutyryl (iBut-), pivaloyl (Piv-), ethoxycarbonyl (Etc-) and nicotinoyl (Nic-) were synthesized, and their lipophilicity was determined by the high-performance liquid chromatography (HPLC) RP method. Statistical analyses of the comparative values of log P and clog P were carried out using computational methods. It was proved that the AC log P algorithm can be useful for the analysis of these compounds and has a statistically justified application in the assessment of the quantitative structure-activity relationship. Moreover, the lipophilicity determined by the HPLC method appears as follows: ACV < Ac- < Nic- < Etc- < iBut- < Piv-.

Novel water-soluble prodrugs of acyclovir cleavable by the dipeptidyl-peptidase IV (DPP IV/CD26) enzyme

We herein report for the first time the successful use of the dipeptidyl peptidase IV (DPPIV/CD26) prodrug approach to guanine derivatives such as the antiviral acyclovir (ACV). The solution- and solid-phase synthesis of the tetrapeptide amide prodrug 3 and the tripeptide ester conjugate 4 of acyclovir are reported. The synthesis of the demanding tetrapeptide amide prodrug of ACV 3 was first established in solution and successfully transferred onto solid support by using Ellman's dihydropyran (DHP) resin. In contrast with the valyl ester prodrug (valacyclovir, VACV), the tetrapeptide amide prodrug 3 and the tripeptide ester conjugate 4 of ACV proved fully stable in PBS. Both prodrugs converted to VACV (for 4) or ACV (for 3) upon exposure to purified DPPIV/CD26 or human or bovine serum. Vildagliptin, a potent inhibitor of DPPIV/CD26 efficiently inhibited the DPPIV/CD26-catalysed hydrolysis reaction. Both amide and ester prodrugs of ACV showed pronounced anti-herpetic activity in cell culture and significantly improved the water solubility in comparison with the parent drug.