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A spectrophotometric method for the quantitative determination of rifampicin in urine is described and its specificity and precision are discussed. It is shown that the mean cumulative urinary elimination of rifampicin is reproducible when the same dose is administered twice in two different experiments to the same group of volunteers. The percentage of the amount eliminated increases with increasing dose. The renal elimination of apparent rifampicin can be used as a parameter for assessment of relative bioavailability of rifampicin from oral dosage forms of the same nominal strength if an appropriate number of volunteers is involved in the test.

Two studies were carried out in man with the aim of assessing the serum and urine concentrations of rifampicin administered by i.v. infusion. In patients suffering from various diseases, a dose of 600 mg i.v. proved to be equieffective with a 600 mg oral dose. Repeated administration of a 600 mg dose by i.v. infusion for a week produced serum levels corresponding to those achieved by oral administration. With the i.v. preparation the drop in serum rifampicin levels during continuous administration was less marked than with the oral administration. The recovery of antibiotic in the urine seems to be lower with i.v. than with the oral preparation. The i.v. preparation was very well tolerated by all the patients.

Two-stage pharmacokinetic studies were conducted in patients suffering from pulmonary tuberculosis treated with rifampicin (RMP). At the first stage of the studies in 100 patients blood and urinary drug levels were determined. The results showed that RMP applied orally penetrates rapidly into the circulation and reaches high serum concentrations varying largely in individual patients. At the second stage of the studies in further 30 patients blood, urinary and sputum RMP levels were simultaneously determined and the biological half-life of RMP and its distribution were checked. It was found that the biological half-life of RMP was 3.79 h, the distribution at the initial stage 38%, and after a few weeks of treatment 52.1%. The authors are of the opinion that the increased value of this parameter has a direct effect on the fall in serum RMP concentration at the later period of treatment. The amount of active RMP excreted by the kidneys of patients with lung tuberculosis averages 33.5%.