Rapid microbiological method for analysis of clindamycin-based product potency and its equivalence to UV and HPLC...

Clindamycin is an antimicrobial sold in capsules, injectable solution, or gel for topical use. Despite its wide use, current official compendia and literature lack microbiological methods to assess its potency, relying mainly on physicochemical assays such as high-performance liquid chromatography (HPLC). These techniques, however, do not evaluate the biological activity of the drug. In this context, the present study proposes, for the first time, aimed to develop and validate a rapid microbiological method to determine the potency of clindamycin in capsule form and to compare its results with those obtained from UV and HPLC methods. The method employed Escherichia coli ATCC 8739, BHI broth as the growth medium, and a hydroalcoholic diluent (ethanol: water, 1:1 v/v) for solution preparation. Concentrations tested were 8, 16, and 32 μg mL^-1, with incubation at 35 ± 2 °C for 4 h under agitation (70 rpm), followed by absorbance measurement at 530 nm. The method exhibited linearity (r > 0.99), selectivity, precision (RSD 3.16 %, 3.57 %, 3.14 %), accuracy (average recovery of 99.47 %), and robustness under most tested conditions, as percentage of inoculum, brand of BHI broth, and volume of BHI broth used in the tube. Statistical comparison confirmed the equivalence of the proposed method with UV and HPLC (F_cal 0.68 < F_tab 5.14). This validated microbiological method offers a fast, reliable, and biologically relevant alternative for routine potency determination of clindamycin capsules, addressing a major analytical gap in the quality control of antimicrobial products.