Metabolite Ritalinic Acid Research Articles

The Pharmacokinetics and Pharmacogenomics of Psychostimulants.

The psychostimulants-amphetamine and methylphenidate-have been in clinical use for well more than 60 years. In general, both stimulants are rapidly absorbed with relatively poor bioavailability and short half-lives. The pharmacokinetics of both stimulants are generally linear and dose proportional although substantial interindividual variability in pharmacokinetics is in evidence. Amphetamine (AMP) is highly metabolized by several oxidative enzymes forming multiple metabolites while methylphenidate (MPH) is primarily metabolized by hydrolysis to the inactive metabolite ritalinic acid. At present, pharmacogenomic testing as an aid to guide dosing and personalized treatment cannot be recommended for either agent. Few pharmacokinetically based drug-drug interactions (DDIs) have been documented for either stimulant.

Development of analytical method for the determination of methylphenidate, the analog ethylphenidate and their metabolite ritalinic acid in oral fluid samples by micro-QuEChERS and liquid chromatography–tandem mass spectrometry

The aim of this study was to develop a quantitative method for the analysis of methylphenidate, the analog ethylphenidate and their metabolite ritalinic acid in oral fluid, using micro-QuEChERS extraction and liquid chromatography–tandem mass spectrometry (LC–MS/MS). Oral fluid samples were collected with Quantisal™ device, extracted by micro-QuEChERS technique and analyzed by LC–MS/MS. The developed method met the validation criteria of Academy Standards Board (ASB) Standard Practices for Method Validation in Forensic Toxicology (Standard 036, 2019) with limits of detection and quantification of 0.5 ng/mL and calibration curve from 0.5 to 50 ng/mL. Within-run imprecision was greater than 18.7% while between-run imprecision was greater than 17.0 % for all analytes. Bias did not vary more than 7.7 %. No evidence of carryover was found. Stability studies presented satisfactory results for 24 h on autosampler (10 °C), after 3 cycles of freeze/thaw, 7 days on freezer (−20 °C) and until 7 days on refrigerator (4 °C) for methylphenidate. The validated method was further successfully applied to the analysis of 5 authentic oral fluid samples collected from volunteers at parties and music festivals from different cities in Brazil. Four samples had positive results for methylphenidate and ritalinic acid, and only one sample was positive for methylphenidate. Ethylphenidate was not detected in the samples. The method showed acceptable analytical performance and is environmentally friendly, requiring reduced use of solvents and reagents, with potential to be applied to clinical and forensic analyses.

Development of Analytical Method for the Determination of Methylphenidate, the Analog Ethylphenidate and Their Metabolite Ritalinic Acid in Oral Fluid Samples by Micro-Quechers and Liquid Chromatography−Tandem Mass Spectrometry

Development of Analytical Method for the Determination of Methylphenidate, the Analog Ethylphenidate and Their Metabolite Ritalinic Acid in Oral Fluid Samples by Micro-Quechers and Liquid Chromatography−Tandem Mass Spectrometry

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: 10mg or 40mg, oral: 40mg). Ethylphenidate was administered and blood and urine samples were collected prior to and for up to 72hours 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 12hours following intravenous administration of 10mg and 40mg and oral administration of 40mg, respectively. Ritalinic acid was non-detectable at 72hours in the group that received a 10-mg intravenous and 40-mg oral dose of ethylphenidate. Ritalinic acid concentrations were below the LOQ at 72hours following intravenous administration of 40mg 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.

Development of a physiologically based model to describe the pharmacokinetics of methylphenidate in juvenile and adult humans and nonhuman primates.

The widespread usage of methylphenidate (MPH) in the pediatric population has received considerable attention due to its potential effect on child development. For the first time a physiologically based pharmacokinetic (PBPK) model has been developed in juvenile and adult humans and nonhuman primates to quantitatively evaluate species- and age-dependent enantiomer specific pharmacokinetics of MPH and its primary metabolite ritalinic acid. The PBPK model was first calibrated in adult humans using in vitro enzyme kinetic data of MPH enantiomers, together with plasma and urine pharmacokinetic data with MPH in adult humans. Metabolism of MPH in the small intestine was assumed to account for the low oral bioavailability of MPH. Due to lack of information, model development for children and juvenile and adult nonhuman primates primarily relied on intra- and interspecies extrapolation using allometric scaling. The juvenile monkeys appear to metabolize MPH more rapidly than adult monkeys and humans, both adults and children. Model prediction performance is comparable between juvenile monkeys and children, with average root mean squared error values of 4.1 and 2.1, providing scientific basis for interspecies extrapolation of toxicity findings. Model estimated human equivalent doses in children that achieve similar internal dose metrics to those associated with pubertal delays in juvenile monkeys were found to be close to the therapeutic doses of MPH used in pediatric patients. This computational analysis suggests that continued pharmacovigilance assessment is prudent for the safe use of MPH.

Ethylphenidate: From biomarker to designer drug

The following is a brief background and account of the psychostimulant "designer drug" and curious methylphenidate-ethanol transesterification metabolite, ethylphenidate (EPH; Fig 1). That is ethylphenidate with an "E", not it's well known homolog, methylphenidate (MPH; Ritalin, Concerta, others) – the first-line agent for the treatment of attention-deficit/hyperactivity disorder (ADHD). Note that the only structural difference resides in the ester where EPH has an ethyl group rather than the methyl group in MPH.

Enantioselective Determination of Methylphenidate and Ritalinic Acid in Whole Blood from Forensic Cases Using Automated Solid-Phase Extraction and Liquid Chromatography-Tandem Mass Spectrometry

A chiral liquid chromatography tandem mass spectrometry (LC-MS-MS) method was developed and validated for quantifying methylphenidate and its major metabolite ritalinic acid in blood from forensic cases. Blood samples were prepared in a fully automated system by protein precipitation followed by solid-phase extraction. The LC-MS-MS method was linear in the range of 0.5 to 500 ng/g for the enantiomers of both analytes. For concentrations above the limit of quantification, coefficients of variation were 15% or less, and the accuracy was 89 to 94%. For 12 postmortem samples in which methylphenidate was not determined to be related to the cause of death, the femoral blood concentration of d-methylphenidate ranged from 5 to 58 ng/g, and from undetected to 48 ng/g for l-methylphenidate (median d/l-ratio 5.9). Ritalinic acid was present at concentrations 10-20 times higher with roughly equal amounts of the d- and l-forms. In blood from 10 living subjects that were not suspected of being intoxicated by methylphenidate, the concentration ranges and patterns were similar to those of the postmortem cases. Thus, methylphenidate does not appear to undergo significant postmortem redistribution.

Determination of methylphenidate and its metabolite ritalinic acid in urine by liquid chromatography/tandem mass spectrometry

Methylphenidate (MPH) is a drug that is licensed for treatment of ADHD and also narcolepsy. Monitoring of the parent drug and its major metabolite ritalinic acid (RA) in urine is considered necessary to ensure compliance with treatment programmes. A rapid, simple and sensitive liquid chromatography/tandem mass spectrometry (LC–MS/MS) assay was developed for the determination of MPH and its metabolite RA in human urine. After urine was diluted with water, methylphenidate, the major metabolite ritalinic acid, and d 6-amphetamine as the internal standard were resolved on a PFP propyl column using gradient elution of 0.02% ammonium formate and acetonitrile. The total analysis time was 13.5 min. The three compounds were detected using electrospray ionisation in the positive mode. Standard curves were linear over the concentration range 5–5000 μg/L ( r > 0.997), bias was ≤±20%, intra- and inter-day coefficients of variation (imprecision) were <8% and the limit of detection was 5 μg/L. The limit of quantitation was set at 100 μg/L. Matrix effects were up to 140% but these were accounted for by the internal standard. The assay is being used successfully in clinical practice to enhance the safe and effective use of methylphenidate.

Determination of methylphenidate and ritalinic acid in blood, plasma and oral fluid from adolescents and adults using protein precipitation and liquid chromatography tandem mass spectrometry—A method applied on clinical and forensic investigations

A validated, accurate and sensitive LC–MS/MS method for determination of racemic methylphenidate and its metabolite ritalinic acid has been developed. The analytes were quantified by tandem mass spectrometry operating in positive electrospray ionization mode with multiple reaction monitoring. Blood, plasma and oral fluid samples of 100 μl were prepared by simple precipitation with 200 μl of an aqueous solution of zinc sulphate in methanol. Corresponding deuterated internal standards were used for quantification. Calibrations for methylphenidate and ritalinic acid were linear within the selected range of 0.2–30 ng/ml and 10–1500 ng/ml in blood or plasma and in the range of 1–500 ng/ml and 0.25–125 ng/ml in oral fluid, respectively. The method was successfully applied for the analysis of samples from patients treated with methylphenidate in the dose range of 36–72 mg/day and some representative ante mortem and post mortem samples from clinical and forensic toxicological investigations. A three to fourfold higher concentration of methylphenidate was found in oral fluid compared with blood while for ritalinic acid the concentrations were about 25-fold lower in oral fluid.

Occurrence and fate of the human pharmaceutical metabolite ritalinic acid in the aquatic system

To investigate the occurrence and fate of ritalinic acid – the main human metabolite of the psychostimulant drug methylphenidate – in the aquatic environment, a HPLC–electrospray–MS/MS method for the quantification of ritalinic acid in wastewater, surface water and bank filtrate was developed. Carbamazepine known as very stable in the aquatic environment was analyzed as anthropogenic marker in parallel. Furthermore, the removal of ritalinic acid was studied in a sewage treatment plant using an activated sludge system during a field study and in lab-scale plants. In good agreement between lab-scale and field studies a low removal rate of 13% and 23%, respectively, was determined. As a consequence, the concentration of ritalinic acid in the wastewater effluents were in the range of <50–170 ng L −1 which corresponds to a mean specific load per capita of 17.7 μg d −1. Ritalinic acid has further been detected in German rivers at concentrations of 4–23 ng L −1 and in bank filtrate samples in 100–850 m distance from the river up to 5 ng L −1 demonstrating the widespread occurrence of this stable metabolite in the aquatic environment. A comparison to available sales data shows that a significant amount of methylphenidate applied can be found in waters as ritalinic acid.

Correlation Between Methylphenidate and Ritalinic Acid Concentrations in Oral Fluid and Plasma

We studied the excretion profile of methylphenidate (MPH) and its metabolite ritalinic acid (RA) in oral fluid and plasma, the oral fluid-to-plasma (OF/P) drug ratio, and the variations of oral fluid pH after drug administration. We analyzed oral fluid and plasma samples, obtained from 8 healthy volunteers after ingestion of a single dose of 20 mg fast-release or extended-release MPH, for MPH and RA by LC-MS. We estimated the apparent pharmacokinetic parameters of MPH in plasma and oral fluid and calculated the OF/P ratio for each time interval. MPH and RA were detected in oral fluid. Whereas parent drug concentrations in oral fluid were an order of magnitude higher than those in plasma, the opposite was observed for RA. Oral fluid concentrations of MPH ranged between 0.5 and 466.7 microg/L and peaked at 0.5 h after administration of the fast-release formulation; they ranged between 0.7 and 89.5 microg/L and peaked at 2 h after administration of the extended-release formulation. Both formulations presented bimodal time-course curves for the OF/P ratio, ranging between 1.8 and 242.1 for the fast-release formulation and between 2.6 and 27.0 for extended-release. Oral fluid pH did not appear to be modified by the administration of the drug, and its influence on OF/P ratio did not affect the correlation of MPH between the 2 body fluids. The results obtained support the measurement of MPH in oral fluid as an alternative to plasma if the extended-release formulation is used.

Pharmacokinetics of methylphenidate in oral fluid and sweat of a pediatric subject

Methylphenidate (MPH) is a stimulant medication widely used for treating attention-deficit hyperactivity disorder (ADHD) in children and adolescents. Therapeutic monitoring for this drug is essentially lacking and alternative biological matrices, such as oral fluid and sweat, should be investigated for noninvasive assessment of short- and long-term history of drug use. We report the excretion profile of MHP and its metabolite ritalinic acid (RA) in oral fluid and sweat from a 12-year-old boy treated with the extended release drug formulation. Concentrations of MPH and RA in oral fluid, sweat and plasma were measured by liquid chromatography–mass spectrometry. Oral fluid-to-plasma ratio at each time interval was calculated at the start of the treatment and correlated with salivary pH. Excretion of MPH in sweat patches, collected up to 24 h with PharmChek patches was also investigated. MPH and RA were both detected in oral fluid with a pharmacokinetic profile similar to that in plasma. Oral fluid peak concentrations of MPH ranged between 13.5 and 30.9 ng/mL at 3.0 h after drug intake. Oral fluid-to-plasma MPH ratio between 13.1 and 3.2 demonstrated an accumulation of the drug in oral fluid. Conversely, RA was found in oral fluid at peak concentration (23.4–62.9 ng/mL) equivalent to one-tenth of those found in plasma. Concentration profiles of MPH and RA in oral fluid were quite constant during the four weeks of drug administration. In sweat, MPH was detected for the first time at 5 h after drug administration (range: 9.3–11.2 ng/patch) up to 24 h (range: 29.8–38.7 ng/patch). RA was not detected in the sweat patches during the 24 h time of collection. The results suggest that measurement of MPH in oral fluid can be used as a potential alternative to drug monitoring in plasma. Moreover, MPH measurement in sweat patches can be used for noninvasive monitoring of MPH consumption and misuse in situations where detection of recent abuse is of interest.

Liquid chromatography–electrospray ionization mass spectrometry determination of methylphenidate and ritalinic acid in conventional and non-conventional biological matrices

A procedure based on liquid chromatography–electrospray ionization mass spectrometry is described for determination of methylphenidate (MPH) and its principal metabolite ritalinic acid (RA) in plasma, urine, oral fluid and sweat using 3,4-methylendioxypropylamphetamine (MDPA) as internal standard. Aliquots of 100 μL biological fluids and sweat patch were initially treated with acetonitrile, centrifuged, and clear supernatants evaporated and redissolved in 10 mM ammonium acetate. Chromatography was performed on a reversed-phase column using a gradient of 10 mM ammonium acetate and acetonitrile as a mobile phase at a flow rate of 1 mL/min. Separated analytes were confirmed and quantified by positive electrospray ionization mass spectrometry and selected ion monitoring acquisition mode. Limits of quantifications were 1 ng/mL plasma, 1 ng/sweat patch, 0.5 ng/mL oral fluid and urine for MHF; 1 ng/mL plasma and oral fluid, 1 ng/sweat patch, 0.5 ng/mL urine for RA using 100 μL biological fluids or one sweat-patch per assay. Calibration curves were linear over the calibration ranges for both MPH and RA, with r 2 > 0.99. At three concentrations spanning the linear dynamic range of the assay, mean recoveries ranged between 67.9–90.3% for MPH and 36.3–92.4% for RA in the different biological matrices. This method was applied to therapeutic monitoring of MHP and RA in conventional and non-conventional biological matrices from individuals in drug treatment.

Analysis of methylphenidate and its metabolite ritalinic acid in monkey plasma by liquid chromatography/electrospray ionization mass spectrometry.

Methylphenidate (MP, Ritalin) is a psychotropic drug widely prescribed to children for treating the symptoms of attention deficit disorder with and without hyperactivity. Because little information exists about the effects of chronic MP administration on cognitive function in children, measures of behavior changes in non-human primates are important surrogates. An essential component of such studies is the determination of MP plasma levels under chronic and acute dosing conditions. An analytical method was developed that provided sufficient sensitivity to measure low levels of the active parent drug (lower limit of quantitation = 0.25 ng/mL) and the inactive metabolite, ritalinic acid (RA), in monkey plasma as well as the ability to conveniently analyze large numbers of samples. The method uses a polymeric reversed-phase sorbent for solid phase extraction, an efficient reverse-phase high performance liquid chromatography (HPLC) separation, deuterated internal standards for isotope dilution quantification of MP and RA, and detection by sensitive electrospray ionization mass spectrometry (ES-MS) with a single quadrupole instrument. The method responses are linear over the range of plasma concentrations of MP and RA observed in monkeys, gives respective analyte recoveries of 75 and 60% with reasonable precision and accuracy, and demonstrates robust MS performance for rapid determination of MP/RA plasma levels. The average peak MP concentration (ca. 16 ng/mL) and half-lives for MP and RA elimination in monkeys (1.79 and 2.31 h, respectively) were not significantly different under acute vs. chronic dosing conditions and were comparable to values previously reported from human studies.

Enantioselective gas chromatographic assay with electron-capture detection for dl-ritalinic acid in plasma

Enantioselective gas chromatographic assays for the quantitation of methylphenidate and its major metabolite ritalinic acid in plasma are described. The procedures involved the extraction of methylphenidate enantiomers from alkanised plasma. The plasma was then washed to ensure complete removal of methylphenidate before saturation with sodium carbonate to promote the extraction of ritalinic acid enantiomers with ethyl acetate-isopropanol (60:40) solvent mixture. Subsequently, ritalinic acid enantiomers were converted back into methylphenidate enantiomers by Fisher-Speier esterification. N-Heptafluorobutyryl- l-prolyl chloride, a chiral acylating reagent, was used to convert the enantiomers of methylphenidate into their corresponding diastereomeric amide derivatives, which were separated cleanly on an achiral capillary column (OV-225) and quantitated with electron-capture detection. The assays were sensitive, reliable and reproducible.