Spectrophotometric and bioassay methods for the estimation of erythromycin formulation

Author(s): Benjamin U Ebeshi*, Adebola Onanuga, Paulette I Oruye

Abstract

Erythromycin is a naturally occurring chemotherapeutic agent used in the treatment of aerobic gram positive cocci, bacilli and a few gram negative organisms. In view of its resurgent use due to resistance to anti-bacterial chemotherapy, the study sets out to provide simple, sensitive and cost-effective analytical and bioassay techniques involving UV-spectrophotometric and Microbiological methods. Method validation was by means of a precision and accuracy assays. Ten brands of erythromycin formulation comprising, seven tablets and three suspension dosage forms were assayed by UV spectrophotometric at the λmax of 285nm and bioassay methods. Thin Layer Chromatographic (TLC) method was used to establish the identity of the active ingredient in the formulations. The spectrophotometric results, expressed as a percentage of stated amounts of erythromycin were 79 - 120%w/w, which shows that 70% of the test samples conformed to the official stated standard. The bioassay determination gave MICs ranging from 0.5-2µg/ml for all the samples, 0.5μg/ml and 1.0μg/ml for reference erythromycin against S. aureus and B. subtilis, respectively. Thus, 80% of the samples met the bioassay requirement. TLC fingerprint gave Rf values ranging from 0.71 - 0.79 for 80% of the samples while the remaining 20% gave no change in colour, elution nor increase in size of the principal spot. Hence, no single method could be adequate in the determination of the quality of pharmaceutical formulations.

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