Determination of telmisartan in human plasma by liquid chromatography–tandem mass spectrometry

A rapid, selective and sensitive method for the determination of the angiotensin II receptor antagonist, telmisartan, in human plasma has been developed. Telmisartan and the internal standard, diphenhydramine, were extracted from plasma using diethyl ether–dichloromethane (60:40, v/v), and separated on a Zorbax extend C18 column using methanol–10 mM ammonium acetate (85:15, v/v) adjusted to pH 4.5 after mixing with formic acid as mobile phase. Detection was carried out by multiple reaction monitoring on a Q-trap™ LC–MS/MS system with an ESI interface. The assay was linear over the range 0.5–600.0 ng/ml with a limit of quantitation of 0.5 ng/ml and a limit of detection of 0.05 ng/ml. Intra- and inter-day precision were <6.7% and <8.1%, respectively, and the accuracy was in the range 88.9–111.0%. The assay was applied to a pharmacokinetic study of telmisartan given as a single oral dose (80 mg) to healthy volunteers.