Rapid determination of rifaximin on dried blood spots by LC-ESI-MS.

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.