Development and validation of an UFLC-MS/MS method for enantioselectivity determination of d,l-thero-methylphenidate, d,l-thero-ethylphenidate and d,l-thero-ritalinic acid in rat plasma and its application to pharmacokinetic study

Chiral separation and quantitation of methylphenidate, ethylphenidate, and ritalinic acid in blood using supercritical fluid chromatography

Supercritical fluid chromatography (SFC) is a technique that analyzes compounds that are temperature-labile, have moderately low weight, or are chiral compounds. Methylphenidate (MPH) is a chiral compound with two chiral centers. MPH has two chiral metabolites, ethylphenidate (EPH) and ritalinic acid (RA). MPH is sold as a racemic mixture. The d-enantiomer of threo-MPH is responsible for medicinal effects. Due to the differing effects of the enantiomers, it is important to analyze the enantiomers individually to better understand their effects. This method utilizes SFCand solid-phase extraction (SPE) to separate and analyze the enantiomers of MPH, EPH, and RA in postmortem blood. The objective of this method was to assess a unique approach with SFC for enantiomeric separation of MPH, EPH, and RA. A SPE method was developed and optimized to isolate the analytes in blood and validated as fit-for-purpose following international guidelines. The linear range for MPH and EPH was 0.25-25 and 10-1000 ng/mL for RA in blood. Bias was -8.6% to 0.8%, and precision was within 15.4% for all analytes. Following method validation, this technique was applied to the analysis of 49 authentic samples previously analyzed with an achiral method. Quantitative results for RA were comparable to achiral technique, whereas there was loss of MPH and EPH over time. The l:d enantiomer ratio was calculated, and MPH demonstrated greater abundance of the d-enantiomer. This is the first known method to separate and quantify the enantiomers of all three analytes utilizing SFC and SPE.

L- and D-threo ethylphenidate concentrations, pharmacokinetics, and pharmacodynamics in horses

Ethylphenidate is a psychostimulant and analog of the commonly prescribed compound, methylphenidate (Ritalin®). There are a limited number of studies describing the disposition and pharmacologic/toxicological effects of ethylphenidate in any species. The abuse potential in equine athletes along with the limited data available regarding administration in horses necessitates further study. The objectives of the current study were to describe drug concentrations, develop an analytical method that could be used to regulate its use, and describe the pharmacodynamic effects of ethylphenidate in horses. To that end, 12 horses were randomized into 3 dose groups (intravenous: 10 mg or 40 mg, oral: 40 mg). Ethylphenidate was administered and blood and urine samples were collected prior to and for up to 72 hours post drug administration. Concentrations of D-threo ethylphenidate and the metabolite ritalinic acid were measured using Liquid Chromatography-tandem Mass Spectrometry. L-threo ethylphenidate concentrations were estimated from D-threo ethylphenidate concentrations. Serum concentrations of ethylphenidate were below detectable levels by 8, 18, and 12 hours following intravenous administration of 10 mg and 40 mg and oral administration of 40 mg, respectively. Ritalinic acid was non-detectable at 72 hours in the group that received a 10-mg intravenous and 40-mg oral dose of ethylphenidate. Ritalinic acid concentrations were below the LOQ at 72 hours following intravenous administration of 40 mg of ethylphenidate. While the number of animals per dose group were small, no stimulatory behavior or significant changes in heart rate were noted. Untoward effects including gastrointestinal adverse effects were noted in all dose groups.