At present, the most important regimen of tuberculosis chemotherapy is a combinationof isoniazid and rifampicin combination, to which either of streptomycin, ethambutol or/and pyrazinamide is added in the earlier stage. If isoniazid is resistant, the efficacy of thisregimen is diminished. In order to confirm this fact, we investigated the prognosis of isoniazid-resistant patients of pulmonary tuberculosis, comparing with that of sensitivepatients or resistant patients to the other anti-tuberculous drugs.
Out 456 patients of pulmonary tuberculosis, who were admitted to our sanatoriumduring 3 years from 1982 to 1984, 196 were culture positive for tubercle bacilli on admission.
They were composed of 128 original treatment cases and 68 re-treatment cases. All of these culture strains were assessed for the grade of resistance to various anti-tuberculousdrugs, according to the sensitivity tests advocated by the Japanese Society for Tuberculosis (1% Ogawa solid media). The criterion of resistance to isoniazid was determined as follows: completely resistant to than 1 μg/
ml or higher, and incompletely resistant to 1 and 5 μg/
ml of isoniazid.
In 128 original treatment cases, 7 patients (5.4%) were completely resistant and 7patients (5.4%) were incompletely resistant to isoniazid. Among these 14 patients (10.9%), only 2 cases failed to convert to negative sputum. The other 126 patients, including notonly sensitive but also resistant cases, converted to negative. It is suggested that no cleardecrease in the efficacy of original treatment is seen, even if drug resistance exists in a fewcases, but we must be careful only for isoniazid-resistant cases, as treatment failure maybe found in a few isoniazid-resistant cases.
In 68 patients of re-treatment group, 23 patients (33.8%) were completely resistant, and 7 patients (10.3%) were incompletely resistant to isoniazid. Among these 30 patients (44.1%), 15 patients failed to convert to negative sputum with various kinds of drugcombination treatment. As a whole, in re-treatment cases, isoniazid resistant patientswere frequently detected, and the more the number of resistant drugs, the less theeffectiveness of treatment. Moreover, much worse results were obtained in patientsshowing double resistance to isoniazid and rifampicin. Therefore, we should choose morecarefully the combination of anti-tuberculous drugs, not to make the other drugs resistant, especially not to make double resistance to isoniazid and rifampicin. But such a choice wasoften very difficult.
Conclusively, isoniazid-resistance, and isoniazid-rifampicin double resistance arethought to give unfavorable influence on the efficacy of isoniazid-rifampicin combinationtreatment, especially in re-treatment. The attenuation of virulence of isoniazid resistanttubercle bacilli was not observed in our patients as the grade of isoniazid resistance was notso high.
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