Assay of rifampicin in serum

Two methods for the assay of rifampicin in serum are described. The first is a conventional plate diffusion method, measuring concentrations down to 0.02 mug/ml, and the second a chemical extraction followed by measurement of the inhibition of uptake of (14)C-uridine by Staphylococcus aureus, which estimates in the range of 0.02 to 0.001 mug/ml. The methods were used to measure serum concentrations in man following doses of about 1050 mg and 75 mg rifampicin.