Pharmacokinetics of zidovudine following intravenous bolus administration of a novel niosome preparation devoid of cholesterol

Abstract

A novel niosome preparation composed of nonionic surfactants, polyglyceryl-3-diisostearate and polysorbate-80, bilayers stabilized by myristyl alcohol instead of cholesterol was developed. Polyglyceryl-3-diisostearate, myristyl alcohol and polysorbate-80 were in 1:2:1 molar ratio in which 85% zidovudine (3'-azido-3'-deoxythymidine, azidothymidine, AZT, CAS 30516-87-1) was found to be encapsulated in aqueous core. Pharmacokinetic and tissue distribution studies were conducted on this niosome preparation using rabbits and albino rats, respectively, as animal models. AZT levels in rabbit serum were higher following application of niosomal AZT than with AZT solution. Such levels were maintained for prolonged time. T1/2 increased, clearance became slow and as a result AUC and AUMC increased and consequently MRT increased following niosomal AZT treatment. Tissue distribution studies on albino rats also confirmed higher concentration and slower decline of serum levels of AZT due to niosomal AZT. In addition niosomal AZT escaped uptake by reticuloendothelial tissues (liver, spleen, and kidney). Invitro release of AZT from niosomes was slow, about 20% releasing in 18 h. The prolonged AZT levels in rabbit serum following the treatment with niosomal AZT appear to be due to the combined effect of slow invivo release and avoidance of extravascular distribution. Though this preparation seems to maintain AZT levels in serum for a prolonged time, its therapeutic efficacy cannot be claimed as the present method estimates total AZT in the preparation and not free AZT. Further no specific experiments were conducted to substantiate its therapeutic effect.