Cremophor-free intravenous microemulsions for paclitaxel II. Stability, in vitro release and pharmacokinetics

Two cremophor-free microemulsion systems LBMW (lecithin:butanol:myvacet:water) and CMW (capmul:myvacet:water), for intravenous (IV) administration of paclitaxel (PAC) were previously developed and characterized. Their chemical stability, in vitro release and pharmacokinetics of PAC were assessed using Taxol (cremophor:ethanol 1:1, 6 mg/ml) as a reference. The shelf-lives of PAC at 25 degrees C in Taxol, LBMW and CMW, in an accelerated stability study, were 71, 57 and 31 days, respectively. The activation energy (Ea) for PAC in Taxol, LBMW and CMW was 23, 16 and 14 kcal/mol, respectively. PAC released from LBMW and CMW using a dialysis technique was significantly slower than that from Taxol. The extents of release of PAC from LBMW and CMW were 25 and 50% of that from Taxol. In vivo pharmacokinetic studies in male Sprague-Dawley rats after IV administration revealed that PAC in LBMW and CMW remained in the systemic circulation five and two times longer and was eight and three times more widely distributed than PAC from Taxol. LBMW and CMW offer a significant clinical advantage in terms of the prolonged half-life and wide tissue distribution, indicating that PAC delivered by these systems intravenously may result in prolonged exposure of PAC to the tumor and subsequently an improved clinical efficacy.