[Urinary excretion of rifampicin in kidney failure when administered alone or together with isoniazid]

Rifampicin excretion with urine and its plasma levels were studied in 46 patients with nephrophthisis treated with rifampicin alone or in combination with isoniazid in doses of 8--10 mg/kg bw with regard to the degree of renal insufficiency. It was shown that excretion of rifampicin with urine decreased with progression of renal insufficiency and had no effect on its plasma levels. The combined use of isoniazid and rifampicin in a single dose was accompanied by a decrease in the latter's excretion with urine and different changes in its plasma concentration. The use of the two drugs for 4--6 weeks resulted in a further decrease in rifampicin excretion with urine not dependent on renal function and in decreased plasma levels of the antibiotic in 1/3 of patients. The findings indicate that the use of rifampicin in a dose less than 10 mg/kg of the body weight in patients with chronic renal insufficiency is not advisable. The absence of rifampicin in the urine specimens collected during the first hours on the 2nd day after its single use or its use for 4--6 weeks indicate that rifampicin does not accumulate in patients with renal insufficiency.