Development and validation of a gradient HPLC method for the determination of clindamycin and related compounds in a novel tablet formulation.

A gradient reversed-phase HPLC method was developed and validated for potency, content uniformity, and impurity determinations for a novel tablet formulation containing clindamycin. The assay utilized UV detection at 214 nm and a Waters Xterra RP18 column (4.6 mm x 100 mm, 3.5 microm). The mobile phases were comprised of pH 10.5, 10 mM carbonate buffer and acetonitrile. Validation experiments were performed to demonstrate specificity, linearity, accuracy (i.e., average recovery from the formulation), precision (i.e., repeatability), limit of quantitation (LOQ), and robustness (i.e., sample solution stability and buffer pH effects on specificity). The assay was shown to be specific for clindamycin, several impurities, and triethyl citrate, a retained excipient that was present in the dosage form. The assay was proved linear (concentration versus peak area) for clindamycin and several select impurities over the ranges of 70-130% and 0.1-5%, respectively. UV relative response factors were determined for the impurities from the linearity data. The accuracy of clindamycin at the targeted assay concentration was 99.2% (n = 3; precision = 0.12%, R.S.D.); accuracy for lincomycin, a structurally related impurity, was 97.4% (n = 3; precision = 3.5%, R.S.D.) at 0.1% of the targeted assay concentration. By demonstrating an acceptable degree of precision for lincomycin at this level, the LOQ was shown to be no higher than 0.1%. The chromatography was virtually unaffected over a mobile phase buffer pH range spanning 0.4 pH units. Sample solutions were stable for 72 h under ambient conditions.