The phamacokinetics in man of a combination of rifampicin and trimethoprim

Abstract

Six volunteers were given 300 mg of rifampicin and 80 mg of trimethoprim 8-hourly for 7 days. Serum and urine levels of both drugs were measured on days 1 and 8 by modified plate diffusion assay methods. The decrease of serum concentrations of both rifampicin and trimethoprim followed first order kinetics. The serum half life of rifampicin was 2.7 h on day 1 and 1.5 h for day 8, the change being attributed to enzyme induction by rifampicin. The serum half-lives of trimethoprim were 6.1 h and 5.4 h on days 1 and 8 respectively. The urinary clearance of trimethoprim from serum was statistically significantly increased on day 8 compared with day 1 whereas the clearance of rifampicin was unchanged. Faecal flora studies were performed on samples collected before treatment, at the end of treatment and one week after completing treatment. No rifampicin resistant organisms were detected in the faeces of volunteers given rifampicin/ trimethoprim. No untoward side effects were observed.