Efficacy of once-weekly isoniazid-streptomycin in preventing relapse of pulmonary tuberculosis.

Two controlled studies were undertaken to assess the efficacy of streptomycin 1 g. or 0.75 g. (by random allocation) plus isoniazid 15 mg./kg. body-weight once-weekly (the SHOW regimen) in the prevention of bacteriological relapse over a 4 year period, in patients with quiescent pulmonary tuberculosis at the end of one year of chemotherapy. In the first study which involved patients with residual cavitation at one year, bacteriological relapse requiring treatment occurred in 3 per cent of 87 patients given the SHOW regimen for 12 months as compared with 21 per cent of 94 patients on a placebo, a high proportion of the relapses in the latter occurred in the 2nd year and with sensitive organisms. In the second study on patients with no residual cavitation at one year, relapse requiring treatment occurred in 2 per cent of 98 patients given the SHOW regimen for 6 months as compared with 1 per cent of 90 patients given isoniazid approximately 4.5 mg./kg. daily for 12 months.