Stability studies and degradation kinetics of some commercially available metronidazole suspensions in Nigeria

Abstract

The present study was undertaken to investigate the effect of temperature on the degradation of metronidazole suspensions commercially available in Nigeria. Six different brands of metronidazole suspension, coded as MTZ A to MTZ F, were evaluated for their active contents using microbiological assay method. They were stored at three different elevated temperatures of 30 °C, 37 °C and 45 °C and at each temperature, the degradation rate constant was determined from a plot of logarithm of concentration versus time. The shelf-life of the various brands of the drug was predicted from Arrhenius equation and compared with their manufacturers’ label claim. Results confirmed that increase in temperature led to increase in the degradation rate constants for the various brands of the drug. The shelf-life ranged from 35.0 to 80.8 weeks for all the brands studied while the percentage of the calculated shelf -life in comparison with the label claim ranged from 29.3 % to 67.3 % of the manufacturers’ stated shelf-life. This study has shown that increase in temperature causes increased degradation of metronidazole suspensions. It may be concluded that some of the metronidazole suspensions commercially available in Nigeria may have expired long before the actual date stated on the product labels.