Development and Validation of a Microbiological Agar Assay for Determination of Thiamphenicol in Soft Capsules

Background: Thiamphenicol belongs to the amphenicol class of antibiotic and possesses a broad-spectrum antimicrobial activity. An alternative microbiological assay for quantification of thiamphenicol in pharmaceutical formulations has not yet been reported in the literature. Objective: This study aimed to develop and validate an agar diffusion method for quantification of thiamphenicol in soft capsules. Methods: The assay was based on the inhibitory effect of thiamphenicol on the following: a strain of Kocuria rhizophila ATCC 9341, used as the test microorganism, Antibiotic 1culture medium, phosphate buffer pH 6, 0, inoculum at a concentration of 1%, as well as standard and sample solutions at the concentrations of 20.0, 40.0 and 80.0 μg mL-1. Results: The method validation yielded good results for the parameters of linearity, precision, accuracy, robustness and selectivity. The experimental statistic results were analyzed using analysis of variance (ANOVA). The method was found to be linear (r2 = 0.9992) in the range of 20-80 μg mL-1, precise (inter-assay R.S.D = 0.09%), accurate (R.S.D. = 4.65%), specific, and robust. Conclusion: The results demonstrated the validity of the proposed bioassay, which allows for reliable quantification of thiamphenicol in a pharmaceutical sample. An alternative methodology for thiamphenicol determination in routine quality control has been reported herein.