Kinetics of rifampicin and isoniazid administered alone and in combination to normal subjects and patients with liver disease.

The possible existence of kinetic interactions between rifampicin and isoniazid and the effect of the concomitant presence of an impaired liver function were investigated in man. In a first study normal healthy subjects and patients with chronic liver disease received, on three different occasions, a single dose of 600 mg rifampicin or isoniazid and of rifampicin and isoniazid associated in randomized sequences. The results have shown that in both groups the serum levels, half-life values, and urinary excretion of each drug given alone are not significantly different from those observed when the other drug is associated. Serum levels and half-life of rifampicin and isoniazid were significantly higher in patients with chronically impaired liver. In a second study, rifampicin and isoniazid were given in combination at the same doses as in the first study over a period of one week. The results have shown a trend to decrease in the serum levels of rifampicin of the healthy subjects and a trend to increase in the patients with chronic liver disease on day 7 of treatment. In both groups a reduction in the half-life of rifampicin was also observed. No changes in serum isoniazid concentrations were observed between day 1 and day 7 in the healthy subjects, whereas a significant increase was observed in the patients. No significant changes in the half-life of isoniazid were observed.