Determination of ketoconazole in capsules by high-performance liquid chromatography and microbiological assay

The development and validation of an HPLC-UV method and a microbiological assay were performed for the analysis of ketoconazole in capsule formulations. The bioassay was developed using a specific agar diffusion technique with the strain of Candida albicans ATCC 18804 as the test organism. The effect of the mobile phase pH in the range of 2.5-7.5 on the retention and tailing factors of the ketoconazole peak was analyzed in the chromatography method and a pH value of 4.5 was considered to be adequate. A prospective validation of both methods showed adequate linearity (r2 > 0.99 for the two methods), precision, (RSD = 2.42% for intraday and 2.69% for interday precision for bioassay; RSD = 0.74% for intraday and 0.66% for interday precision for HPLC-UV), and accuracy (mean recoveries were 103 +/- 1.0% for bioassay and 99 +/- 1.0% for HPLC-UV). Student's t-test revealed no significant difference between the results obtained by the two methods (P < 0.05). The contents found for three capsule samples showed a strong correlation, as attested by Pearson's coefficient value (r = 0.9998), which also evidenced the concordance between the studied methodologies.