Esterification of Cidofovir with Alkoxyalkanols Increases Oral Bioavailability and Diminishes Drug Accumulation in Kidney

Smallpox was eradicated by vaccination in the 1970s. However, concerns have arisen about the potential use of variola virus as a biological weapon. Most of the world's population has little residual immunity because systematic vaccination against smallpox ceased in the early 1970s. Vaccination of key elements of the population against smallpox is again being considered. However, there are now large numbers of persons who cannot be safely vaccinated with the current vaccine because of AIDS, immunosuppressive drugs, and certain common skin disorders. It would be useful to have a potent orally active drug as an alternative for these persons in case of an outbreak of smallpox. Alkoxyalkyl esters of cidofovir (CDV) have been shown to be highly active and selective against poxviruses in vitro with activities several logs greater than the activity of unmodified CDV. This is due in large part to increased cellular penetration and conversion to CDV-diphosphate, the active antiviral. In this paper, the oral pharmacokinetics of 14C-labeled hexadecyloxypropyl-cidofir (HDP-CDV), octadecyloxyethyl-cidofir (ODP-CDV), and oleyloxypropyl-cidofir (OLP-CDV) are examined and oral bioavailability and tissue distribution assessed and compared with parenteral CDV. The alkoxyalkyl CDVs are highly orally bioavailable and do not concentrate in kidney, the site of the dose-limiting toxicity of CDV. Plasma and tissue drug levels are many times greater than the in vitro EC(50s) for variola, cowpox, and vaccinia viruses. Thus, the compounds are good candidates for further development for prevention and treatment of smallpox infection and the complications of vaccination.