Development and Validation of Microbiological Assay for Ceftriaxone and its Application in Photo-stability Study

The aim of this work is to develop and validate a microbiological assay for ceftriaxone with a view to the employment of this method to assess photo-stability in commercial products. The experimental conditions included: (1) ceftriaxone standard solution in concentrations of 2.6 μg/mL, 3.2 μg/mL, 4.0 μg/mL, 5.0 μg/mL and 6.3 μg/mL, using phosphate buffer pH 6.0 as diluent, (2) Petri dishes prepared by adding 21-mL of antibiotic medium as base layer and 4-mL of the same medium, inoculated with Bacillus subtilis (ATCC 6633) in a proportion of 0.5% and (3) incubation at 37ºC for 18 hours. The method showed specificity, good linearity in the range from 2.6 to 6.3 μg/mL, as well as good precision (RSD repeatability of 1.7% and RSD intermediate precision of 2.2%) and accuracy (recovery of 101.1%). Commercial samples of ceftriaxone were exposed to light in their primary and secondary packing, being afterwards directly exposed to light. The potencies of commercial samples were then determined by the developed and validated microbiological assay. The results indicate that primary and secondary packing provide satisfactory protection of ceftriaxone from light.