Chemotherapeutic agents for the treatment of pulmonary tuberculosis have been with us now for nearly thirty years but only comparatively slowly have we learnt how best to deploy them. As a result of a mixture of clinical experience and well-planned controlled clinical trials, we learnt that the use of any single agent alone would lead to a substantial proportion of treatment failures due to the development of bacteriological resistance. This problem was virtually overcome when two or more drugs were used in combination but gradually it became clear that the duration of chemotherapy would have to be prolonged way beyond that employed for most other bacterial infections, failing which a substantial proportion of patients would relapse, with re-emergence of tubercle bacilli in their sputum. This is exemplified by the results of the controlled clinical trial initiated by the British Medical Research Council in 1956 in which different durations of therapy with a combination of PAS plus isoniazid, supplemented in some instances by an initial course of streptomycin, were compared in patients with chronic cavitated tuberculosis. (see Table 1).
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J H Angel (1977) studied this question.