Rapid determination of rifaximin in rat serum and urine by direct injection on to a shielded hydrophobic stationary phase by HPLC.

A simple and rapid reversed-phase HPLC method for determination of rifaximin in rat serum and urine was developed. Separation of rifaximin from biological matrix was achieved by direct injection of rat serum and urine onto a restricted-access medium, Supelco LC-Hisep, a shielded hydrophobic stationary phase, using acetonitrile:water:acetic acid (18:82:0.1 v/v/v) as a mobile phase. The linear range was 0.10-20 microg/mL (r(2 )> 0.999, n = 6), intraday and interday variation was <6.10%. The limits of detection and quantification were 0.03 (signal-to-noise ratio >3) and 0.10 microg/mL (signal-to-noise ratio >10), respectively. The method was successfully applied to pharmacokinetic studies of rifaximin after an oral administration to rats.