Chromosomal studies in vivo and in vitro of trimethoprim and sulphamethoxazole (co-trimoxazole)

Because both trimethoprim (TMP) and sulphamethoxazole (SMX) could interfere with folate metabolism and the former is a pyrimidine analogue it seemed advisable to try to ascertain whether these drugs alone, or in combination, determine damage in human chromosomes.In nine patients who had been taking a standard daily dosage of co-trimoxazole for periods varying from 3 to 112 weeks no damage in chromosomes of lymphocytes was found. In vitro experiments were cultured in concentrations of TMP and SMX considerably higher than the steady state plasma levels of patients being treated with the combination of drugs, also showed no chromosomal damage.