Oral Fluid Drug Testing: Analytical Approaches, Issues and Interpretation of Results

With advances in analytical technology and new research informing result interpretation, oral fluid (OF) testing has gained acceptance over the past decades as an alternative biological matrix for detecting drugs in forensic and clinical settings. OF testing offers simple, rapid, non-invasive, observed specimen collection. This article offers a review of the scientific literature covering analytical methods and interpretation published over the past two decades for amphetamines, cannabis, cocaine, opioids, and benzodiazepines. Several analytical methods have been published for individual drug classes and, increasingly, for multiple drug classes. The method of OF collection can have a significant impact on the resultant drug concentration. Drug concentrations for amphetamines, cannabis, cocaine, opioids, and benzodiazepines are reviewed in the context of the dosing condition and the collection method. Time of last detection is evaluated against several agencies' cutoffs, including the proposed Substance Abuse and Mental Health Services Administration, European Workplace Drug Testing Society and Driving Under the Influence of Drugs, Alcohol and Medicines cutoffs. A significant correlation was frequently observed between matrices (i.e., between OF and plasma or blood concentrations); however, high intra-subject and inter-subject variability precludes prediction of blood concentrations from OF concentrations. This article will assist individuals in understanding the relative merits and limitations of various methods of OF collection, analysis and interpretation.

Precise simultaneous quantification of methadone and cocaine in rat serum and brain tissue samples following their successive i.p. administration

A sensitive high-performance liquid chromatography (HPLC) assay with dual UV detection has been developed and validated for the simultaneous quantification of methadone and cocaine in rat serum and brain tissue samples. Liquid-liquid extraction using hexanes was applied for samples extraction with Levo-Tetrahydropalmatine (L-THP) as the internal standard. Chromatographic separation of the analytes was achieved on a reversed-phase Waters Symmetry^® C₁₈ column (150mm×4.6mm, 5μm). A gradient elution was employed with a mobile phase consisting of 5mM potassium phosphate containing 0.1% triethylamine (pH=6.5) (A) and acetonitrile (B) with a flow rate of 1mL/min. UV detection was employed at 215nm and 235nm for the determination of methadone and cocaine, respectively. The calibration curves were linear over the range of 0.05-10μg/mL for both methadone and cocaine. The assay was validated according to FDA guidelines for bioanalytical method validation and results were satisfactory and met FDA criteria. Inter-day accuracy values of serum and brain samples ranged from 96.97 to 105.59% while intra-day accuracy values ranged from 91.49 to 111.92%. Stability assays showed that both methadone and cocaine were stable during sample storage, preparation, and analytical procedures. The method was successfully used to analyze biological samples obtained from a drug- drug interaction pharmacokinetics (PK) study conducted in rats to investigate the effect of methadone on cocaine PK. Our method not only can be used for bioanalysis of samples obtained from rats but also can potentially be applied to human biological serum samples to monitor compliance to methadone maintenance therapy (MMT) and to detect possible cocaine-methadone co-abuse.

Determination and Validation of a Solid-phase Extraction Gas Chromatography-mass Spectrometry for the Quantification of Methadone and Its Principal Metabolite in Human Plasma

This study aimed to develop a solid-phase extraction gas chromatography-selected ion monitoring-mass spectrometry method for the determination of methadone (MDN) and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP) in human plasma. The linear response was obtained over the concentration range from 10 to 2000 ng/mL for MDN and EDDP. The absolute recoveries of MDN and EDDP were 95.9%–98.9% and 94.8%–102.4%, with relative standard deviation (RSD) ranging from 1.8% to 2.7% and 1.8% to 3.9%, respectively. The intra- and interday precisions were found to be less than 5% for both analytes. The limits of detection of MDN and EDDP were 4 and 5 ng/mL, respectively. The presented method was convenient for therapeutic drug monitoring and pharmacokinetic studies in patients on heroin-assisted MDN therapy.