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A highly sensitive and selective on-line two-dimensional reversed-phase liquid chromatography/electrospray ionization-tandem mass spectrometry (2D-LC-ESI/MS/MS) method was developed and validated to determine rifaximin in rat serum by direct injection. The 2D-LC-ESI/MS/MS system consisted of a restricted access media column for trapping proteins as the first dimension and a Waters C(18 )column as second dimension using 0.1% aqueous acetic acid:acetonitrile as mobile phase in a gradient elution mode. Rifampacin was used as an internal standard. The linear dynamic range was 0.5-10 ng/mL (r(2) > 0.998). Acceptable precision and accuracy were obtained over the calibration range. The assay was successfully used in analysis of rat serum to support pharmacokinetic studies.

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The use of blood spot collection cards is a simple way to obtain specimens for therapeutic drug monitoring, assessing adherence to medications and preventing toxicity in a clinical setting. A high-throughput liquid chromatography-electrospray ionization mass spectrometric (LC-ESI-MS) method for determination of rifaximin on dried blood spots (DBS) was developed and validated. It involves solvent extraction of a punch of DBS followed by reversed-phase LC on a monolithic column consisting of a silica rod with bimodal pore structure and detection by ESI-MS. Rifampicin was used as an internal standard (IS). The run time was within 5.0 min with a very low back-pressure at a flow rate of 0.5 mL/min. The assay was linear from 0.1 to 10 ng/mL. The mean recovery was 98.42%. The developed method is very simple, rapid and useful for clinical applications.