Drug resistance among previously treated tuberculosis patients, a brief report.

The choice of an appropriate chemotherapeutic regimen for the treatment of tuberculosis is more difficult if the patient has been treated for tuberculosis in the past. This study was undertaken to determine drug-resistance rates among patients previously treated with isoniazid (INH), streptomycin (SM), and/or paraaminosalicylic acid (PAS). The study population consisted of 4,017 patients for whom the length and type of previous therapy was known. Forty-one per cent of these patients were found to be excreting organisms resistant to 1 or more of the following 3 drugs: INH, SM, and PAS. Resistance to INH was encountered most (36.8%), followed by resistance to SM (19.2%), and resistance to PAS (17.2%). Resistance rates were considerably higher among the 1,168 patients who had previously received monotherapy (60%) than among those who had never received single-drug therapy (33%). In general, the percentage of patients excreting resistant organisms increased with increasing duration of the previous therapy. The implications of these findings for the design of retreatment regimens are discussed.

The incidence of cancer among participants in controlled, randomized isoniazid preventive therapy trial.

Cancer morbidity and mortality were examined among 11,894 Puerto Rican participants in a US Public Health Service preventive therapy trial begun in 1957. The mean duration of follow-up was 18 years (range 16-19 years). No statistically significant difference in overall cancer rates was observed between the participants in the trial assigned isoniazid and those assigned placebo. There were also no significant differences between the groups when rates for specific types of cancer and age-specific cancer rates were compared. No trend toward an increasing cancer rate in the isoniazid group was observed with the passage of time. The mortality rate due to cancer was similar in the two groups. These data coupled with other information reported in the literature provide substantial evidence that isoniazid, when given in the usual therapeutic doses, is not carcinogenic in humans.