Determination of paclitaxel and related taxanes in bulk drug and injectable dosage forms by reversed phase liquid chromatography

Baseline separation of 15 taxanes including paclitaxel (Taxol) was achieved on pentafluorophenyl (PFP) HPLC columns. Methods using aqueous acetonitrile gradients on each of two commercial PFP columns were developed that are suitable for the determination of potency, content uniformity, and degradation profile of the paclitaxel bulk drug and injectable dosage form. The elution order is apparently related to molecular size, the number of acetylated hydroxyl groups, and the substitution of a xylosyl group at the 7-position. The resolution of several of the taxanes is a sensitive function of the starting eluent composition and the programming rate, which requires optimization of the methods on both columns. Retention of 10 of the taxanes was studied over the temperature range from 30 to 70 degrees C, and enthalpies of transfer, delta H degree, were determined. Conversion of a hydroxy group to an acetyl group, which can interact more strongly with the fluorines on the PFP, has a large effect on the delta H degree, as does the addition of a xylosyl derivative to the 7-hydroxy. The methods developed for the injectable drug form allow good resolution of the taxanes from the excipient Cremophor EL, a polyethoxylated castor oil used with ethanol to solubilize the paclitaxel. The methods for the bulk drug were fully validated in terms of accuracy, precision, specificity including forced degradation, limits of detection and quantitation, and linearity and range.