Further study on the cytogenetic effects of combined chemotherapy with isoniazid and para-aminosalicylic acid on human lymphocytes in vivo: sister chromatid exchanges, chromosome aberrations in first-division metaphases, cell growth kinetics, and mitotic index.

Tuberculosis patients under therapy with the drug combination isoniazid (INH) and para-aminosalicylic acid (PAS) were screened to investigate the cytogenetic effects. Results were compared with those from the patient controls (ie, tuberculosis patients before starting drug therapy) and general controls (individuals from the general population). The induction of chromosome aberrations was homogeneous and increased significantly in all the drug-exposed patients, whereas the frequency of sister chromatid exchanges (SCEs) was increased only in one of them. These results indicated differences in the two processes: chromosome aberrations and SCEs. Patients under therapy exhibited no change in cell growth kinetics, but the mitotic index was slightly enhanced compared to patient controls. It is concluded that the drug combination of INH + PAS induces damage in lymphocyte chromosomes in vivo. Further studies should be carried out on germ cells.