Cytogenetic effects of chemotherapy with three combinations of anti-tubercular drugs involving isoniazid, thiacetazone, para-aminosalicylic acid and streptomycin on human lymphocytes: chromosome aberrations, sister chromatid exchanges and mitotic index.

Cytogenetic effects of three combinations of anti-tubercular drugs were evaluated on human lymphocytes in vivo and were compared with controls of two types: (1) newly diagnosed tuberculosis patients before starting therapy and (2) individuals from the general population. The drugs used were: isoniazid (INH), thiacetazone (TAZ), para-aminosalicylic acid (PAS), and streptomycin (SM). These drugs were tested in the following combinations: (a) INH + TAZ + SM, (b) INH + PAS + SM, (c) INH + SM. The frequency of chromosome aberrations was significantly increased in patients treated with both the triple drug combinations, i.e., with INH + TAZ + SM and INH + PAS + SM, whereas patients treated with INH + SM did not exhibit an increase in the frequency of chromosome aberrations as compared to the controls. Although both the triple drug combinations were clastogenic, none of the three drug combinations tested induced an increase in the frequency of sister chromatid exchanges (SCEs). In other words, the mechanisms leading to SCEs and chromosome aberrations may be different. SM appeared to depress the mitotic index in patients treated with INH + SM and INH + PAS + SM, though it was found to possess a mild anti-clastogenic effect. INH + TAZ + SM, on the other hand, enhanced the mitotic index. This enhanced mitotic index was probably due to the presence of TAZ.