Miniaturized Microbiological Method to Determine the Potency of Rifaximin in Tablets

BACKGROUND: Rifaximin, a semi-synthetic antimicrobial, does not present microbiological method described in official compendia, and there is a lack of literature on this topic. The quality control of antimicrobials is extremely important to evaluate the real potency of pharmaceutical products. OBJECTIVE: A miniaturized turbidimetric method for determining the potency of rifaximin in tablets was developed and validated by turbidimetry, according to the international guidelines. METHOD: Escherichia coli ATCC 10536 IAL 2393, brain heart infusion (BHI) broth, inoculum at 8%, rifaximin in purified water with 20% ethanol at 5, 10, and 20 μg/mL and 530 nm were used. RESULTS: The method was considered selective for rifaximin, as the adjuvants did not show activity; linear with correlation coefficients 0.9998 for standard and 0.9999 for sample; accurate with 99.73% recovery; precise with RSD less than 3%; and robust in the face of small variations in (i) rifaximin volume, (ii) proportion of ethanol, (iii) inoculum volume. CONCLUSIONS: The method is considered adequate and safe to evaluate the potency of rifaximin in tablets, contemplating speed, low cost, low waste generation, and ease of operation. HIGHLIGHTS: This work usescurrent, sustainable, and green analytical chemistry and can be used in the routine analyses of rifaximin by laboratories and the pharmaceutical industry around the world.