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 (0.02ng/mL) and N-oxide (0.04ng/mL).•The method was validated in the concentration range of 0.02–10ng/mL and 0.04–50ng/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, 0.375mg, 0.5mg.•More detailed PK profiles of roflumilast and N-oxide were captured taking benefits of the rather low LLOQs.