Stability-indicating liquid chromatographic determination of etoposide and benzyl alcohol in injectable formulations

Simple and specific assays for etoposide, related impurities, and benzyl alcohol, as well as its degradation product, benzaldehyde, in injectable formulations were developed using high-performance liquid chromatography (HPLC). Etoposide, benzyl alcohol, benzaldehyde, and four etoposide impurities were determined with a mobile phase containing 26% acetonitrile in pH 4.0 acetate buffer with methyl p-aminobenzoate as the internal standard. Two etoposide precursors were additionally determined using 60% acetonitrile in the mobile phase with biphenyl as the internal standard. The assays were run sequentially. The etoposide assay had a total variability of less than 1% (RSD) and a recovery from placebo of 99.4%. Mean recovery of impurity standards spiked at the 2% level relative to the etoposide level was 98%. Recoveries for benzyl alcohol and benzaldehyde were 100.5% and 102.2%, respectively. Absorbance ratios generated from samples and compared with undegraded standards demonstrated specificity for etoposide. Similar response regression equations with correlation coefficients greater than 0.99 were obtained for etoposide and four impurities over the 2-8 micrograms/mL concentration range, indicating that an etoposide standard could be used to quantitate low impurity levels down to 0.2% relative to the etoposide injectable concentration. Benzaldehyde could be reliably detected at concentrations down to 0.5 micrograms/mL, equivalent to 0.16% of the benzyl alcohol level.