Cremophor-free intravenous microemulsions for paclitaxel I: formulation, cytotoxicity and hemolysis

Two cremophor-free microemulsions, lecithin:butanol:myvacet oil:water (LBMW) and capmul:myvacet oil:water (CMW) for paclitaxel (PAC) were developed for intravenous (i.v.) administration. Six surfactants and four oils were screened with various combinations for maximal water incorporation and PAC solubility. Microemulsion regions were subsequently determined in ternary phase diagrams. Cytotoxicity in an MDA-M231 human breast cancer cell line and hemolytic potential were assessed in these systems compared to Taxol (cremophor EL:ethanol, 1:1, 6 mgPAC/ml). The maximal water incorporation into the lecithin:butanol surfactant blend was greater than that incorporated into capmul when combined with the oils screened. PAC solubility in myvacet oil was increased 1389-fold over its aqueous solubility. LBMW had a larger microemulsion region (46.5% of total ternary phase diagram) than that seen with CMW (18.6%). The droplet size of the dispersed phase was 111.5 (4.18)nm for LBMW and 110.3 (8.09)nm for CMW. Cytotoxicity of PAC was in decreasing order of: Taxol>LBMW>CMW. The IC50 values for LBMW and CMW ranged from 4.5 to 5.7 and >10 microM, respectively, as compared to that of Taxol (1.3 to 1.8 microM). Eighty-three percent, 68%, and 63% of red blood cells remain unlysed at a formulation volume to blood ratio of 0.035 in LBMW, CMW and Taxol. Promising microemulsions, LBMW and CMW were developed that can incorporate approximately 12 mg/g of PAC, substantially higher than its aqueous solubility (10.8 microg/ml) and that in the Taxol vehicle (6 mg/ml). PAC retained its cytotoxicity in the LBMW and CMW and was less likely to cause hemolysis compared to Taxol. This higher drug loading results in a smaller vehicle volume in required doses of these formulations and potentially less vehicle-related side effects are anticipated.