Effect of temperature on storage of ethionamide during susceptibility testing

Objective: Ethionamide being thermolabile in nature, effect of temperature on the drug and its stability in liquid and solid media during susceptibility testing procedures was assessed to understand the inconsistency in DST formats. Methods: Working solution of ethionamide and LowensteinJensen (LJ) media incorporated with ethionamide were preincubated at 4°C and 37°C prior to DST methods was incubated till 4 weeks at different temperatures and utilized for DST in MGIT 960. Results: Degradation of ethionamide working solution was observed at 37°C after 3 weeks of incubation. Ethionamide incorporated LJ media can be stored without compromise on susceptibility up to 5 weeks. But, a week of prior incubation at 37°C has deleterious effect on the DST profile. Ethionamide was found to degrade at 37°C after different time points when stored as solution or as LJ media. Conclusion: Use of DST formats that provide results within 2 weeks can be recommended for ethionamide susceptibility testing. J Microbiol Infect Dis 2013; 3(3): 128-132