A Pharmacokinetic Study of Methylphenidate Hydrochloride Multilayer Extended-Release Capsules (Aptensio XR®) in Preschool-Aged Children with Attention-Deficit/Hyperactivity Disorder.

OBJECTIVE: This was a single-dose, one-period, multicenter, pharmacokinetic (PK) study to evaluate the PK of methylphenidate (MPH) hydrochloride multilayer extended-release capsules (MPH-MLR) in preschool children aged 4 to < 6 years, previously diagnosed with attention-deficit/hyperactivity disorder (ADHD), and on a stable dose of MPH. METHODS: Preschool-aged children (N = 10) received a single oral dose of MPH-MLR (10, 15, or 20 mg) sprinkled over applesauce; a dose equivalent to their pre-enrollment daily dose of MPH. Blood samples for the measurement of MPH concentrations were obtained pre-dose and at 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 h post-dose. No structural model was assumed in the derivation of PK values for analysis. Maximum plasma concentration (Cmax), area under the concentration-time curve (AUC), elimination half-life, clearance (CL), and volume of distribution (Vd) data were compared with a historical group of older children aged 6-11 years (N = 11) and analyzed by bodyweight. Safety (adverse event monitoring, vital signs, electrocardiogram, clinical laboratory testing, physical examination) was assessed. RESULTS: Mean dose-normalized Cmax and area under the curve to the last measurable observation (AUC0-t) values were similar across dose groups, ranging from 0.67 ng/mL/mg (MPH 15 mg) to 0.81 ng/mL/mg (MPH 10 mg) for Cmax/dose, and from 7.80 h × ng/mL/mg (MPH 20 mg) to 8.92 h × ng/mL/mg (MPH 10 mg) for AUC0-t/dose. PK results were integrated into a previously described pharmacostatistical population PK model. Visual predictive check plots showed greater variability in the 6- to 11-year-old group than the 4- to < 6-year-old group, and CL increased with increasing body weight in a greater than dose-proportional manner. Mean CL, normalized for body weight, was constant for all dose groups, ranging from 4.88 L/h/kg to 5.80 L/h/kg. Median time to Cmax ranged from 2.00 to 3.00 h post-dose, and overall, dose-normalized Cmax concentrations indicated greater systemic exposures of MPH-MLR in preschool children aged 4 to < 6 years compared with children aged 6-11 years. Children aged 4 to < 6 years had a lower Vd than children aged 6-11 years. There were no unexpected safety signals. CONCLUSION: The PK of MPH-MLR in preschool children demonstrated the biphasic absorption profile described earlier in older children, and the PK profile in children with ADHD aged 4 to < 6 years was similar to the profile in those aged 6-11 years, apart from a lower Vd and relatively higher systemic MPH levels for children in the preschool group. TRIAL REGISTRATION: Clinicaltrials.gov Identifier: NCT02470234.

Analytically Confirmed Intoxication by 4-Fluoromethylphenidate, an Analog of Methylphenidate.

4-Fluoromethylphenidate (4F-MPH) is an halogenated derivative of methylphenidate (MPH), a re-uptake inhibitor for dopamine and norepinephrine used for the treatment of attention deficit hyperactivity disorders. In the last few years, several compounds structurally related to MPH have been marked as new psychoactive substances (NPS) with stimulating and euphoric effects similar to the parent drug, but with more dopaminergic activity. This report represents the first case of an analytically confirmed non-fatal intoxication by 4F-MPH. A 26-year-old female was admitted to the emergency department with neuropsychiatric and cardiologic symptoms that lasted for a week, during which she sniffed a powder named 4F-MPH acquired as entactogen on the Internet. The patient required sedation with intravenous diazepam and was discharged two days later with a prescription of promazine and quetiapine. The seized product was analytically characterized by gas chromatography-mass spectrometry, liquid chromatography high-resolution mass spectrometry and nuclear magnetic resonance. These analyses confirmed the composition of the product as a 4F-MPH diastereomeric (±)-threo and (±)-erythro mixture, with a large preponderance of the active (±)-threo isomer. A minimal validation, intended for rare analytes, was performed for the quantification of 4F-MPH in the biological samples by liquid chromatography-tandem mass spectrometry. Accuracy (bias) and precision were within ±15% for both blood and urine. The blood and urine concentration of (±)-threo 4F-MPH were 32 ng/mL and 827 ng/mL, respectively. Analyses for classic drugs (opiates, methadone, cocaine, cannabis metabolites, amphetamines, ecstasy and LSD), ethanol, qualitative full screen by gas chromatography-mass spectrometry and targeted analysis for 50 NPS by liquid chromatography-tandem mass spectrometry tested negative; comorbidities were excluded, too. Based on these data, it can be assumed that the clinical manifestations were due to 4F-MPH only.

Postmortem Brain-Blood Ratios of Amphetamine, Cocaine, Ephedrine, MDMA and Methylphenidate.

Brain tissue may serve as a useful supplement to blood in postmortem investigations. However, reference concentrations for central stimulant drugs are scarce in brain tissue. This study involves some frequently used stimulants: amphetamine, cocaine, ephedrine, MDMA and methylphenidate. We present concentrations from brain and blood and brain-blood ratios of the analytes from autopsies. The cases were grouped according to the cause of death: A: The compound solely caused a fatal intoxication. B: The compound contributed to a fatal outcome in combination with other drugs, alcohol or disease. C: The compound was not related to the cause of death. Analyses were carried out using solid-phase extraction and ultra high-performance liquid chromatography. Paired brain and femoral blood concentrations from 133 cases were analysed. Positive correlations were observed for all analytes with correlation coefficients ranging from 0.58 to 0.95. The following median brain-blood ratios were obtained: cocaine 2.0 (range 0.20-7.0), amphetamine 3.2 (range 1.5-4.5), ephedrine 2.3 (range 1.1-6.2), MDMA 3.9 (range 0.92-5.1) and methylphenidate 2.4 (0.92-4.6). The concentrations in femoral blood generally agreed with the literature for all compounds. The metabolite of cocaine, benzoylecgonine, was also quantified in brain and blood from 60 cases, and the median brain-blood ratio was 0.66 with 10-90 percentiles of 0.39-1.27. The results of this study can aid the toxicological investigation in determining the cause of death.

Novel and rapid LC-MS/MS method for quantitative analysis of methylphenidate in dried blood spots.

AIM: Development and validation of a novel, sensitive, specific and rapid dried blood spots (DBS)-LC-MS/MS method for methylphenidate (MPH), an attention-deficit hyperactivity disorder drug. Methodology & results: Protein precipitation with acetonitrile was used to extract MPH from the DBS cards. Chromatographic separation was achieved on a Zorbax C18 column using an isocratic mobile phase composed of acetonitrile and 5 mM ammonium formate buffer (20:80, v/v) at a flow rate of 0.5 ml/min. MPH was quantified over a linear range of 200-25,000 pg/ml. CONCLUSION: The clinical DBS-LC-MS/MS method was successfully validated as per the US FDA's Bioanalytical Method Validation Guidance to support an ongoing pediatric pharmacokinetic study.

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.

Interindividual and Intraindividual Variation of Methylphenidate Concentrations in Serum and Saliva of Patients With Attention-Deficit/Hyperactivity Disorder.

BACKGROUND: Therapeutic drug monitoring is becoming increasingly important in psychiatric therapy, especially in children. However, for several reasons, it cannot yet be implemented as a daily routine in clinical or outpatient settings. To evaluate new, noninvasive procedures, blood and saliva (oral fluid) samples were collected from patients with attention-deficit/hyperactivity disorder (ADHD) who were also being administered methylphenidate (MPH). The study's main purposes were to correlate MPH concentrations in serum and saliva between subjects and to analyze intraindividual variation of serum concentration. METHODS: Thirty-six patients with ADHD (27 children and 9 adults) on MPH medication were included for drug analysis. MPH and its major metabolite ritalinic acid were quantified using liquid chromatography-tandem mass spectrometry measurements. The following correlations were investigated: (1) between drug concentrations in serum and saliva, and (2) between pH value and saliva to serum concentration ratio. Furthermore, the mean intraindividual MPH-concentration fluctuation in saliva under constant frame conditions was analyzed. RESULTS: After quantification, MPH concentrations were approximately 5 times higher in the saliva than in the serum, whereas the concentrations of ritalinic acid were much lower in saliva. We found significant correlations between concentrations of MPH in serum and saliva (r = 0.51, P < 0.05). Saliva MPH measures, compared with serum, were pH-dependent (r = -0.56, P < 0.01). Daily coefficient of variance of saliva concentration in children taking constant medication was 27.3% (11%-42%), whereas the coefficient of variance for the ratio of saliva to serum was 122% (2%-2060%). CONCLUSIONS: Our data indicate that the interindividual variation in saliva to serum concentrations is rather high, whereas the intraindividual variation is fairly low, as already shown in the literature for repeated citalopram serum measurements. Saliva may well serve as an alternative matrix for therapeutic drug monitoring of MPH in patients with ADHD, especially for follow-up examinations. Future research should focus on analyzing the relationship between drug levels in saliva and clinical effects as well as on understanding the mechanisms that generate saliva drug concentrations. These are essential steps before potential clinical use.

Solid phase microextraction combined with thermal-desorption electrospray ionization mass spectrometry for high-throughput pharmacokinetics assays.

Labor- and time-intensive sample preparation and liquid chromatography mass spectrometry (LC-MS) analysis are required for traditional pharmacokinetics (PK) studies. In order to simplify and accelerate the analytical process of the PK study, solid phase microextraction (SPME) combined with thermal desorption-electrospray ionization/mass spectrometry (TD-ESI/MS) was developed for rapid characterization of trace drug in biological fluids. Methylphenidate in plasma was extracted and concentrated by direct immersion SPME using fused-silica fibers coated with polydimethylsiloxane. The analytes on the SPME fiber were then characterized by TD-ESI/MS. Matrix-matched calibration with multiple reaction monitoring analysis was conducted to quantify methylphenidate. A linear calibration curve was constructed over a concentration range of 0.2-25 ng mL-1 (r = 0.997). The quantitative results obtained by SPME-TD-ESI/MS were validated by LC-MS/MS. The average relative error for both methods was found to be -5.3%. As a viable alternative to LC-MS, SPME-TD-ESI/MS enables simple, rapid, and high-throughput analysis of drugs in plasma. The developed approach is particularly beneficial to PK studies for a very small sample volume (10 µL) is needed, the extraction time is as short as 3 min, and the detection time is less than 30 s.

Fed and Fasted Administration of a Novel Extended-Release Methylphenidate Orally Disintegrating Tablet Formulation for the Treatment of ADHD.

Extended-release methylphenidate is a first-line treatment for attention-deficit/hyperactivity disorder. A methylphenidate extended-release orally disintegrating tablet (MPH XR-ODT) has recently been developed. Here we report an open-label, randomized, 2-period, 2-treatment crossover study to determine the effect of food on the bioavailability of a single 60-mg dose of MPH XR-ODT in healthy adults. Blood samples were collected predose through 36 hours postdose. Maximum plasma concentration (Cmax ), time to maximum plasma concentration (Tmax ), terminal elimination half-life (T1/2 ), overall systemic exposure (AUClast and AUCinf ), and partial areas under the concentration curve (AUC0-3 , AUC3-7 , and AUC7-12 ) were calculated. In total, 48 participants completed the study. For total methylphenidate from MPH XR-ODT, the lower limit of the 90% confidence interval (CI) around the geometric mean ratio (GMR, fed/fasted) for Cmax was below 80%, indicating a slightly decreased rate of absorption with food, whereas the 90%CIs around the GMRs of AUClast and AUCinf were within the 80%-125% limits, suggesting no food effect on exposure. The most common adverse events (AEs) were palpitations and decreased appetite. No serious, unusual, or unexpected AEs were reported. Thus, food had no substantial effect on overall bioavailability of MPH XR-ODT, which may be an important factor for some patients.

A Comparison of the Pharmacokinetics of Methylphenidate Extended-Release Orally Disintegrating Tablets With a Reference Extended-Release Formulation of Methylphenidate in Healthy Adults.

Extended-release (ER) methylphenidate (MPH) is a first-line treatment for attention-deficit/hyperactivity disorder. A methylphenidate extended-release orally disintegrating tablet (MPH XR-ODT) has recently been developed. This was a randomized, open-label, 3-period, 3-treatment study comparing the bioavailability and absorption of 2 MPH XR-ODT formulations with an MPH ER reference medication. Here we report the 2 treatments comparing the commercial MPH XR-ODT formulation and reference medication. Following a ≥10-hour fast, 42 healthy adults received 60 mg of reference medication or MPH XR-ODT (2 × 30 mg). The following pharmacokinetic (PK) parameters were calculated for total methylphenidate (d + l): maximum plasma concentration (Cmax ), time to maximum plasma concentration (Tmax ), terminal half-life (T1/2 ), and areas under the concentration-time curve from time zero to the time of the last quantifiable concentration (AUClast ), and from time zero extrapolated to infinity (AUCinf ). Secondary PK end points included partial AUCs. Safety was also assessed. Overall systemic exposure to methylphenidate after MPH XR-ODT administration was similar to that of the reference product, and the concentration-time profiles for MPH XR-ODT and the reference drug were similar, although the Cmax was 25% higher for MPH XR-ODT. The most common treatment-emergent adverse events were nausea (6) and anxiety (4), which were similar across treatments.

Ethanol Interactions With Dexmethylphenidate and dl-Methylphenidate Spheroidal Oral Drug Absorption Systems in Healthy Volunteers.

BACKGROUND/PURPOSE: Ethanol coadministered with immediate-release dl-methylphenidate (dl-MPH) or dexmethylphenidate (d-MPH) significantly increases the geomean maximum plasma concentration (Cmax) of d-MPH 22% and 15%, respectively, and elevates overall drug exposure and psychostimulant effects. We asked the question: Are these ethanol-MPH interactions based more fundamentally on (1) inhibition of postabsorption d-MPH metabolism or (2) acceleration of MPH formulation gastric dissolution by ethanol in the stomach? This was investigated using the pulsatile, distinctly biphasic, spheroidal oral drug absorption systems of dl-MPH and d-MPH. METHODS: In a randomized, 4-way crossover study, 14 healthy subjects received pulsatile dl-MPH (40 mg) or d-MPH (20 mg), with or without ethanol (0.6 g/kg), dosed 4 hours later. These 4 hours allowed the delayed-release second MPH pulse to reach a more distal region of the gut to preclude gastric biopharmaceutical influences. Plasma was analyzed using a highly sensitive chiral method. Subjective/physiological effects were recorded. FINDINGS/RESULTS: Ethanol increased the second pulse of d-MPH Cmax for dl-MPH by 35% (P < 0.01) and the partial area under the plasma concentration curve from 4 to 8 hours by 25% (P < 0.05). The respective values for enantiopure d-MPH were 27% (P = 0.001) and 20% (P < 0.01). The carboxylesterase 1-mediated transesterification metabolite ethylphenidate served as a biomarker for coexposure. Ethanol significantly potentiated stimulant responses to either formulation. IMPLICATIONS/CONCLUSIONS: These findings support drug dispositional interactions between ethanol and MPH as dominant over potential biopharmaceutical considerations. Understanding the pharmacology underlying the frequent coabuse of MPH-ethanol provides rational guidance in the selection of first-line pharmacotherapy for comorbid attention-deficit/hyperactivity disorder-alcohol use disorder.

Metabolic Patterns of Fentanyl, Meperidine, Methylphenidate, Tapentadol and Tramadol Observed in Urine, Serum or Plasma.

Drug testing is a useful tool to identify drug use or monitor adherence to prescription drugs. The interpretation of drug results can be complicated based on the pattern and proportional concentrations of drugs and/or drug metabolite(s). The purpose of this retrospective study was to detect the positivity rates and metabolic patterns of five prescription drugs, including fentanyl, meperidine, methylphenidate, tapentadol and tramadol. Retrospective data were retrieved from the laboratory information system in a national reference laboratory. Drug testing was performed using four mass spectrometry methods that were validated for clinical use. For urine specimens, the positivity rate was the highest for methylphenidate (62.3%, n = 2,489), followed by tramadol (43.7%, n = 3,483), fentanyl (41.9%, n = 4,657), tapentadol (37.9%, n = 736) and meperidine (8.3%, n = 138). Among positive samples, both parent drug and metabolite(s) was detectable in 94.9% of meperidine samples, 94.5% of tramadol samples, 93.8% of fentanyl samples, 89.9% of methylphenidate and 86.6% of tapentadol samples. For serum or plasma specimens, the positivity rate was the highest for tapentadol (75.0%, n = 39), followed by methylphenidate (74.2%, n = 569), fentanyl (53.6%, n = 113), meperidine (41.9%, n = 18) and tramadol (28.9%, n = 213). Similar metabolic patterns were found in serum or plasma. Of positive results, both parent drug and metabolite(s) were found in 94.7% of fentanyl samples, 83.3% of meperidine samples, 79.6% of methylphenidate samples, 53.8% of tapentadol samples and 44.1% of tramadol samples. Our data demonstrates the metabolic patterns of five drugs from a random urine or serum/plasma collection in patients that have been prescribed these medications. The data presented can be used to guide clinicians in determining drug adherence by assessing the positivity rates of the parent drug and corresponding metabolite(s).

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.

A chiral UFLC-MS/MS method was established and validated for quantifying d-threo-methylphenidate (d-threo-MPH), l-threo-methylphenidate (l-threo-MPH), d-threo-ethylphenidate (d-threo-EPH), l-threo-ethylphenidate (l-threo-EPH) and d,l-threo-ritalinic acid (d,l-threo-RA) in rat plasma over the linearity range of 1-500ng/mL. Chiral separation was performed on an Astec Chirobiotic V2 column (5µm, 250×2.1mm) with isocratic elution using methanol containing 0.003% ammonium acetate (w/v) and 0.003% trifluoroacetic acid (v/v) at a flow of 0.3mL/min. All analytes and IS were extracted from rat plasma by a one-step liquid-liquid extraction (LLE) method. The intra- and inter-run accuracies were within 85-115%, and the intra- and inter-run precision were <10% for all analytes. Extraction recoveries were 55-62% for d-threo-MPH, 54-60% for l-threo-MPH, 55-60% for d-threo-EPH, 53-57% for l-threo-EPH and 25-30% for d,l-threo-RA. The validated UFLC-MS/MS method successfully applied to the pharmacokinetic interaction study of oral d-threo-MPH and l-threo-MPH (alone or in combination) in female Sprague Dawley rats. The EPH was not detected in rat plasma following oral administrated MPH without EtOH. As far as it is known to the authors, this study is the first one step liquid-liquid extraction method to extract and UFLC-MS/MS method to quantify d-threo-MPH, l-threo-MPH, d-threo-EPH, l-threo-EPH and d,l-threo-RA simultaneously.

A review of ethylphenidate in deaths in east and west Scotland.

Ethylphenidate is a psychostimulant and analogue of methylphenidate. Interestingly it is also produced as a metabolite from the co-ingestion of methylphenidate and alcohol (ethanol). In the UK, between April and June 2015, ethylphenidate and 6 other methylphenidate based novel psychoactive substances (NPS) were subjected to a temporary class drug order under the Misuse of Drugs Act 1971. Ethylphenidate is being abused by both novel and habitual drug users, more prominently in the East of Scotland. What is unknown in the literature is the contribution of ethylphenidate in deaths. A search was conducted for an 18 month period (July 2013 to December 2014) to identify cases where ethylphenidate was detected during post-mortem toxicological analysis. Nineteen cases were identified and these cases were examined with regards to case circumstances, pathology findings, toxicology results and adverse effects. The individuals ranged in age from 20 to 54 (median 37) and the majority were male (n=14) and from the East of Scotland (n=16), more specifically Edinburgh and surrounding area. Current or previous heroin abuse was a common theme in these cases (n=16) and injection was a common route of administration of "legal highs" or "burst". The concentration of ethylphenidate in the cases ranged from 0.008 mg/L to over 2 mg/L in post-mortem femoral blood (median 0.25 mg/L, average 0.39 mg/L). Other drugs commonly detected were benzodiazepines (n=15), followed by opiates (n=11, 4 of which were positive for 6-monoacetylmorphine) and then methadone (n=8). All 19 cases received a full post-mortem examination and there were 10 cases where drug toxicity was the sole or potentially contributory factor to the cause of death. Ethylphenidate was specifically mentioned in the cause of death for 5 cases, chronic intravenous (IV) drug use was named as part of the cause of death for 2 cases and in 6 cases there was evidence of complications and infections through IV drug use. As far as it is known to the authors, this is the first review of post-mortem cases involving the use of ethylphenidate in East and West Scotland. This study can be used as a guide for toxicologists and pathologists when interpreting cases which are positive for ethylphenidate.

A pharmacokinetic model of oral methylphenidate in the rat and effects on behavior.

Most animal studies using methylphenidate (MP) do not administer it the same way it is administered clinically (orally), but rather by injection, resulting in an altered pharmacokinetic profile (quicker and higher peak concentrations). We evaluated several oral-dosing regimens in rats, including dual-dose drinking, to mimic clinical drug delivery. Using an 8-hour-limited-access-drinking-paradigm, MP solutions were delivered at different doses (20, 30, or 60mg/kg/day; as well as dual-dosages of 4 and 10mg/kg/day, 20 and 30mg/kg/day, or 30 and 60mg/kg/day, in which the low dose was administered in the first hour of drinking followed by 7 h of drinking the high dose). Plasma was assayed for MP levels at many time points. Results showed that an 8-hour limited drinking of a dual-dosage 30/60mg/kg MP solution achieved a pharmacokinetic profile similar to clinically administered doses of MP at the high end of the spectrum (peaking at ~30ng/mL), while the 4/10mg/kg MP dual-dosage produced plasma levels in the range produced by typically prescribed clinical doses of MP (peaking at ~8ng/mL). Treatment with the higher dual-dosage (HD: 30/60mg/kg) resulted in hyperactivity, while the lower (LD: 4/10mg/kg) had no effect. Chronic effects of these dual-dosages were assessed throughout three months of treatment and one month of abstinence, beginning in adolescence. MP dose-dependently decreased body weight, which remained attenuated throughout abstinence. MP decreased food intake during early treatment, suggesting that MP may be an appetite suppressant and may also speed metabolism and/or suppress growth. Chronic HD MP resulted in hyperactivity limited during the dark cycle, decreased exploratory behavior, and increased anxiolytic behavior. Findings suggest that these dual-dosage-drinking-paradigms can be used to examine the effects of clinically relevant pharmacokinetic doses of MP and that chronic treatment with such dosages can result in long-lasting developmental and behavioral changes.

Plasma Methylphenidate Levels in Youths With Attention Deficit Hyperactivity Disorder Treated With OROS Formulation.

BACKGROUND: There are limited studies investigating the relationship between oral release osmotic system-methylphenidate (OROS-MPH) doses and plasma methylphenidate (MPH) concentrations in children and adolescents. The aim of this study was to investigate the relationship between the doses of OROS-MPH and the plasma levels of the drug. We also examined the effects of the other drugs including aripiprazole, risperidone, fluoxetine, and sertraline on the levels of the MPH in the plasma. METHODS: The files of 100 attention deficit hyperactivity disorder (ADHD) subjects (76 male, 24 female) who were diagnosed as ADHD according to the Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition criteria, were screened. The ages of subjects were between 6 and 18 years (mean = 11.5 ± 3.8 years). Plasma MPH levels were determined by high-performance liquid chromatography-tandem mass spectrometry assay. RESULTS: Daily mean OROS-MPH dose used in ADHD children was 0.7 ± 0.2 mg/kg (range: 0.3-1.3 mg/kg). The mean plasma OROS-MPH was 11.6 ± 7.3 ng/mL (range: 0.5-43.4 ng/mL). There was no group difference in the mean plasma MPH and dose-related MPH levels between the groups that used any additional drug including aripiprazole (n = 25), risperidone (n = 10), fluoxetine (n = 16), sertraline (n = 10), and did not use these drugs (P > 0.05). There was a positive correlation between the OROS-MPH doses (mg/kg) and the blood MPH levels (Pearson correlation = 0.40; P < 0.001). The plasma levels of MPH were found to be less than 13 ng/mL in 65% of the subjects. CONCLUSIONS: Our findings point to the fact that plasma levels of MPH show a wide range of changes at similar doses, correlate positively with the doses and, as expected, are not affected by using risperidone, sertraline, fluoxetine, and aripiprazole. Therapeutic drug monitoring may help to optimize MPH dose in patients not responding to treatment or in those experiencing serious side effects, but not in routine clinical practice. The presence of intermediate dose formulations such as 45-mg tablets for OROS-MPH may contribute to the optimization.

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.

Methylphenidate intoxication: somnolence as an uncommon clinical symptom and proof of overdosing by increased serum levels of ritalinic acid.

There is considerable evidence for an increase of methylphenidate (MPH) abuse; thus, physicians might be confronted more frequently with MPH intoxications. Possible symptoms of intoxications with MPH are orofacial, stereotypic movements and tics as well as tachycardia, cardiac arrhythmias, arterial hypertension, hyperthermia, hallucinations and epileptic seizures. Here we report a patient who demonstrated somnolence as an uncommon clinical feature of MPH intoxication. The patient exhibited subnormal MPH serum levels (3 µg/l), however markedly increased serum levels of ritalinic acid (821 µg/l; inactive metabolite of MPH), that finally confirmed the initially suspected MPH intoxication. Due to the short half-life of orally administered MPH (t1/2~3 h) the sole measurement of MPH serum levels might be misleading concerning the proof of MPH overdosing in some cases. Parallel measurement of MPH and ritalinic acid is recommended in cases with suspected MPH intoxication and insufficient anamnestic data.

[LC-MS/MS assay of methylphenidate: stability and pharmacokinetics in human].

The study aims to solve the instability problem of methylphenidate (MPH) in plasma, and establish a LC-MS/MS method for simultaneous determining of MPH in human plasma. The stabilities of MPH in different media were studied, and the degradation characteristics of MPH in these media were also investigated by HPLC and LC-MS/MS. To a 200 microL aliquot of freshly collected plasma sample, 10 microL 2% formic acid was added immediately to prevent the hydrolysis of MPH in human plasma samples. Chromatographic separation was performed on a Sapphire C18 column using the mobile phase of methanol - 5 mmol.L-1 ammonium acetate buffer solution containing 0.1% formic acid (46 : 54). MPH was quantified by tandem mass spectrometry operating in positive electrospray ionization mode with multiple reaction monitoring. The detection used the transitions of protonated molecules at m/z 234.2-->84.1 for MPH and m/z 260.3-->183.1 for propranolol (IS), separately. The intra- and inter-assay precisions were all below 5.0%. The accuracies were all in standard ranges. The linear calibration curve was obtained in the concentration range of 0.035-40 ng.mL-1. The methods fulfilled the demand. The method was used to determine the concentration of MPH in human plasma after a single dose of 36 mg MPH tablet to 6 healthy Chinese volunteers. The method is suitable for the precisely determination of MPH and for pharmacokinetic study of MPH in human plasma.

Abuse liability assessment in preclinical drug development: predictivity of a translational approach for abuse liability testing using methylphenidate in four standardized preclinical study models.

OBJECTIVES: Preclinical abuse liability assessment of novel clinical CNS-active candidates involves several tests, addressing different aspects characteristic for abuse potential, which are considered predictive for substance abuse of these candidates, thus ensuring an appropriate translational approach. To demonstrate how such a strategy could work, a known drug of abuse, methylphenidate was evaluated in a full rodent test battery, comprising four test models, and in accordance with the requirements of the FDA, ICH and EMA guidelines. METHODS: Methylphenidate was tested orally at 2.5, 5 or 10mg/kg for its physical dependence potential in a repeated dose non-precipitated withdrawal test, for its drug profiling in a drug discrimination learning procedure (single escalating doses), and for its reinforcing properties in a conditioned place preference test (alternate dosing days) and an intravenous self-administration procedure (0.05 to 1mg/kg/IV infusion during 5 daily 1-h test sessions). The stimulant d-amphetamine served as positive control and was administered subcutaneously at 0.8mg/kg in the first three test models. In the intravenous self-administration procedure rats were habituated to intravenously self-administer d-amphetamine at 0.06mg/kg/IV infusion prior to methylphenidate substitution. RESULTS: Cessation of subchronic dosing up to 10mg/kg methylphenidate led to sustained or even exacerbated effects on locomotion and behavior, body temperature, body weight, food consumption, and alteration of the diurnal rhythm during withdrawal. Clear generalization to d-amphetamine was obtained in the drug discrimination test at 5 and 10mg/kg. Distinct reinforcing properties were present in the conditioned place preference test at 10mg/kg and in the intravenous self-administration study from 0.05mg/kg/IV infusion onwards. The maximum plasma exposure after oral administration of methylphenidate over the dose ranges tested in the present rat studies covered at least 1.9-fold to 18.9-fold the recommended human therapeutic exposure of 10ng/ml, a plasma level that is considered representative of the human efficacious methylphenidate dose. The ratio Cmax Hu/rat calculated from the intravenous self-administration data ranged from 14.9 to 576.5. Consequently the regulatory requirements, stating that preclinical drug abuse liability studies should include high doses that produce plasma levels that are multiples of the therapeutic dose were fulfilled (FDA, EMA, ICH). DISCUSSION: The presented preclinical models, implemented within a drug development environment, were considered highly predictive to assess the abuse potential of methylphenidate, and in accordance with the regulatory requirements of drug licensing authorities in terms of appropriate methods, dose selection and subsequent plasma exposure.