Simultaneous determination of roflumilast and its metabolite in human plasma by LC–MS/MS: Application for a pharmacokinetic study

• An LC–MS/MS method was developed for the detection of roflumilast and roflumilast N-oxide (N-oxide) in human plasma.
• The lower limits of quantitation (LLOQs) were rather low for both roflumilast (0.02 ng/mL) and N-oxide (0.04 ng/mL).
• The method was validated in the concentration range of 0.02–10 ng/mL and 0.04–50 ng/mL for roflumilast and N-oxide.
• The method was applied for a PK study of roflumilast in Chinese heathy subjects after oral dose of 0.25 mg, 0.375 mg, 0.5 mg.
• More detailed PK profiles of roflumilast and N-oxide were captured taking benefits of the rather low LLOQs.

Roflumilast had shown good efficacy and safety in Caucasian COPD patients after oral administration of 0.5 mg. The main active metabolite of it is roflumilast N-oxide. A reliable liquid chromatography–tandem mass spectrometry (LC–MS/MS) quantitation method was developed for the simultaneous determination of them in human plasma with rather low limits of quantitation for roflumilast (0.02 ng/mL) and roflumilast N-oxide (0.04 ng/mL). Human plasma samples were prepared by solid phase extraction (SPE), which ensured high recovery and slight matrix effect for the both analytes. This method showed good linearity, accuracy, precision and stability in the range of 0.02–10 ng/mL and 0.04–50 ng/mL for roflumilast and roflumilast N-oxide respectively. The developed method was successfully applied for the pharmacokinetic research in Chinese healthy volunteers after oral administration of 0.25 mg, 0.375 mg and 0.5 mg of roflumilast tablet.