High-pressure liquid chromatographic quantitation of rifampin and its two major metabolites in urine and serum.

Rifampin and two of its major metabolites, 25-O-desacetylrifampin and 3-formylrifamycin SV, were quantitated in serum, urine, and aqueous solutions by high-pressure, reverse-phase liquid chromatography. This rapid, precise, and simple method utilizes a single-step extraction, dual-wavelength monitoring, and quantitation by comparison of the absorbance of the drug or metabolite with that of an internal standard; the wavelengths used are 337 nm and 254 nm. The degrees of precision are +/- 1.3% and + 4.0% for rifampin only (within run and run to run); recovery in the assay is linear, with concentrations of up to 20 micrograms/ml. Comparison of this method with the reference bioassays yielded a good correlation (r = .975). Short turnover time and small sample size make the assay ideal for the monitoring of therapeutic drug concentrations and for pharmacokinetic studies.