Tuberculosis and Trimethoprim-Sulfamethoxazole

The sulfonamides were the first drugs with antituberculous effects. Their use was abandoned and basically forgotten with the advent of streptomycin and isoniazid combination treatment. There is a widespread belief, apparently based on testing a single isolate on questionable media, that Mycobacterium tuberculosis is resistant to trimethoprim-sulfamethoxazole (TMP-SMX). We saw a complex immunocompromised patient with tuberculosis who was initially treated with TMP-SMX without antituberculous drugs and defervesced on this treatment. An isolate of M. tuberculosis from this patient was found to be sensitive to TMP-SMX. We examined how frequently M. tuberculosis is sensitive to TMP-SMX. Isolates were tested for susceptibility to TMP-SMX on supplemented Middlebrook 7H10 plates. We found that 43 of 44 (98%) isolates of M. tuberculosis were susceptible to the combination of < or = 1 microg/ml of TMP and 19 microg/ml of SMX (< or = 1/19 microg/ml). Thus, the vast majority of our M. tuberculosis isolates were susceptible to TMP-SMX at an MIC similar to that for Mycobacterium kansasii, Mycobacterium marinum, and sensitive rapidly growing mycobacteria, organisms successfully treated with TMP-SMX as part of the treatment regimen. It is possible that TMP-SMX may be useful in treating patients with multiple-drug-resistant and extended drug-resistant tuberculosis. We feel that a clinical trial looking at the effectiveness of TMP-SMX as an antituberculous drug is worthwhile.