TB regimens and anti-TB drug formulations have changed regularly in the past in response to new insights and circumstances in TB control. The introduction of rifampicin in the 1970s shortened the regimen from 12-18 months to 6-8 months (short course chemotherapy: SCC). In the 1990s, SCC was expanded worldwide together with the expansion of DOTS strategy. More recently, the majority of countries using DOTS strategy have replaced rifampicin and isoniazid loose tablets with combination tablets (2-drug FDCs [RH]) as recommended by WHO and IUATLD since 1994. Since the early 1990s, many high HIV prevalence countries have replaced thioacetazone with ethambutol or rifampicin in the continuation phase and some countries have also changed from a daily to intermittent treatment regimen. The 1997 WHO Model List of Essential Medicines recommended the use of rifampicin 150 mg + isoniazid 75 mg (R150 mg + H75 mg) instead of the previously recommended rifampicin 150 mg + isoniazid 100 mg (R150 mg + H100 mg) and pyrazinamide 400 mg (Z400 mg) instead of pyrazinamide 500 mg (Z500 mg). All these changes were included in guidelines and training, and have been implemented at local level, resulting in increased DOTS efficiency.
Since 1999, 4-drug FDCs have been proposed for the initial phase of treatment of category 1 and 2 patients. Availability on the international market, quality and price no longer represent an obstacle. Considering the advantages, e.g. simpler prescription, decreased chance to select resistant strains, and increased patient and health worker acceptance, it is expected that 4-drug FDCs will become the standard formulation for TB regimens in the very near future.