Withania somnifera (WS) is one of the popular botanical medicines widely used in Ayurveda. Withanolides such as withaferin A (WA) and withanolide A (WLD) are its bioactive constituents reported as promising drug candidates in cancer and neurological disorders respectively. A new, selective and rapid high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method has been developed and validated for simultaneous determination of WA and WLD in mice plasma. Simple liquid-liquid extraction procedure was followed using ter-butyl methyl ether (TBME) for plasma sample pretreatment. Analytes were separated on Hypurity C18 column using methanol and ammonium acetate (95:5, v/v) as a mobile phase and detected by electrospray ionization in the multiple reaction monitoring (MRM) mode. The mass transition ion-pair was followed as m/z 471.3→281.2 for WA; m/z 437.2→292.2 for tianeptine (IS) and m/z 488.3→263.1 for WLD; m/z 315.9→270 for clonazepam (IS). The method showed excellent linearity (r(2)>0.997) over the concentration range of 0.484-117.880ng/ml for WA and from 0.476-116.050ng/ml for WLD. The lower limits of quantification (LLOQs) were found to be 0.484ng/ml and 0.476ng/ml for WA and WLD respectively. Precision (% CV) and accuracy (% bias) were found in the range of 3.7-14.3% and -14.4-4.0%, respectively. The validated method was successfully applied to a pharmacokinetic (PK) study for estimation of WA and WLD in mice plasma following oral administration of W. somnifera root aqueous extract (WSE). The PK study suggested rapid oral absorption of these withanolides. The PK study revealed that withaferin A has one and half times more relative bioavailability as compared to withanolide A.
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