Quantitative determination of the enantiomers of methadone in human plasma and saliva by chiral column chromatography coupled with mass spectrometric detection

• Published in: Talanta (Oxford) 2016-03, Vol.149, p.142-148
• Main Authors: George, Rani, Lobb, Michael, Haywood, Alison, Khan, Sohil, Hardy, Janet, Good, Phillip, Hennig, Stefanie, Norris, Ross
• Format: Article
• Language: English
• Subjects: Adsorption; Adult; Chromatography, High Pressure Liquid; Enantiomers; HPLC–MS/MS; Humans; Methadone; Methadone - analysis; Methadone - blood; Plasma; Plasma - chemistry; Saliva; Saliva - chemistry; Tandem Mass Spectrometry
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2015.11.044

Methadone is a potent lipophilic synthetic opioid that is effective in the treatment of cancer pain and perceived benefit in difficult pain control scenarios (especially in cases of neuropathic pain). The use of methadone in clinical practice is challenging however, due to the narrow therapeutic window and large inter- and intra-individual variability in therapeutic response. Quantitation of the enantiomers d- and l-methadone (d- and l-MTD) in plasma and saliva provides a basis for studying its pharmacokinetics in patients with cancer and for monitoring efficacy, toxicity and side-effects. This assay involves quantitation of the enantiomers of methadone using their respective deuterated internal standards, in plasma and saliva matrices with no impact of ion suppression in either matrix. The analytical recoveries of d- and l-MTD from the saliva collection devices (Salivette®) are optimised in this novel method with an accurate and simple extraction method employing dichloromethane. Optimal enantioselective separations were achieved using an α1-acid glycoprotein chiral stationary phase and triple quadrupole tandem mass spectrometer. Linearity was demonstrated over 0.05–1000µg/L for both enantiomers in plasma and in saliva with correlation coefficients greater than 0.998. The lower limit of quantitation (LLOQ) was determined to be 0.1µg/L in plasma and saliva for d- and l-MTD. Accuracy of the method ranges from 100% to 106% even at the LLOQ and total precision, expressed as the coefficient of variation, was between 0.2% and 4.4% for both analytes in both matrices. A simple one step extraction procedure resulted in recoveries greater than 95% for both analytes, at concentrations as low as 0.5µg/L, from the Salivette®. The validated method was applied successfully in 14 paired plasma and saliva samples obtained from adult patients with cancer pain receiving methadone. [Display omitted] •A highly sensitive HPLC–MS/MS method for quantitation of methadone enantiomers.•Validated in plasma and saliva matrices, using Salivettes® for saliva collection.•Applicable for studies in cancer patients with very low saliva sample volume.•Novel one step extraction of methadone from saliva samples collected in Salivettes®.•Nonspecific adsorption of methadone to Salivettes® is addressed.