Clinical correlates of methylphenidate blood levels

A Practical, Evidence-informed Approach to Managing Stimulant-Refractory Attention Deficit Hyperactivity Disorder (ADHD)

Stimulants (methylphenidate or amphetamines) are the recommended first-line option for the pharmacological treatment of individuals with attention deficit hyperactivity disorder (ADHD). However, some patients with ADHD will not respond optimally to stimulants. Here, we discuss strategies to manage stimulant-refractory ADHD, based on the recommendations advanced in clinical guidelines, knowledge of expert practice in the field, and our own clinical recommendations, informed by a comprehensive literature search in PubMed, PsycInfo, EMBASE + EMBASE classic, OVID Medline, and Web of Science (up to 30 March 2021). We first highlight the importance of stimulant optimization as an effective strategy to increase response. We then discuss a series of factors that should be considered before using alternative pharmacological strategies for ADHD, including poor adherence, time action properties of stimulants (and wearing-off of effects), poor tolerability (that prevents the use of higher, more effective doses), excessive focus on or confounding from presence of comorbid non-ADHD symptoms, and tolerance. Finally, we consider the role of non-stimulants and combined pharmacological approaches. While the choice of medication for ADHD is still to a large extent based on a trial-and-error process, there are reasonably accepted data and guidelines to aid in clinical decision-making. It is hoped that advances in precision psychiatry in the years ahead will further guide prescribers to tailor medication choice to the specific characteristics of the patient.

Psychotropic drug concentrations and clinical outcomes in children and adolescents: a systematic review

INTRODUCTION

The use of psychotropic drugs in children and adolescents is widespread but associated with suboptimal treatment effects. Therapeutic drug monitoring (TDM) can improve safety of psychotropic drugs in children and adolescents but is not routinely performed. A major reason is that the relationship between drug concentrations and effects is not well known.

AREAS COVERED

This systematic review evaluated studies assessing the relationship between psychotropic drug concentrations and clinical outcomes in children and adolescents, including antipsychotics, psychostimulants, alpha-agonists, antidepressants, and mood-stabilizers. PRISMA guidelines were used and a quality assessment of the retrieved studies was performed. Sixty-seven eligible studies involving 24 psychotropic drugs were identified from 9,298 records. The findings were generally heterogeneous and the majority of all retrieved studies were not of sufficient quality. For 11 psychotropic drugs, a relationship between drug concentrations and side-effects and/or effectiveness was evidenced in reasonably reported and executed studies, but these findings were barely replicated.

EXPERT OPINION

In order to better support routine TDM in child- and adolescent psychiatry, future work must improve in aspects of study design, execution and reporting to demonstrate drug concentration-effect relationships. The quality criteria proposed in this work can guide future TDM research. Systematic review protocol and registration PROSPERO CRD42018084159.

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.

Stimulant 'rapid metabolizers': wrong label, real phenomena

This is a review of the empirical literature regarding what has been described anecdotally as patients who are 'rapid metabolizers' of stimulant medication. The authors propose that this is a misnomer used to describe two types of atypical pharmacokinetic patterns of response: high-dose responders, short-duration responders and two types of atypical pharmacodynamics patterns of response: patients who develop either acute or chronic tolerance. The authors propose that use of more precise terminology should facilitate both patient education and research to better understand the physiology and clinical management of atypical response patterns to stimulant treatment. Presently, the understanding of the pharmacokinetics and pharmacodynamics of psychostimulants is still quite limited. Further scientific research is needed to understand unusual patterns of pharmacological response seen in the clinic. Careful identification and precise description of these patterns would facilitate understanding the pharmacokinetics and pharmacodynamics of stimulants impacts the atypical response patterns seen in the clinic.

The impact of CES1 genotypes on the pharmacokinetics of methylphenidate in healthy Danish subjects

AIMS

This study investigated the influence of CES1 variations, including the single nucleotide polymorphism (SNP) rs71647871 (G143E) and variation in copy number, on the pharmacokinetics of a single oral dose of 10 mg methylphenidate.

METHODS

CES1 genotype was obtained from 200 healthy Danish Caucasian volunteers. Based on the genotype, 44 (19 males and 25 females) were invited to participate in an open, prospective trial involving six predefined genotypes: three groups with two, three and four CES1 copies, respectively; a group of carriers of the CES1 143E allele; a group of individuals homozygous for CES1A1c (CES1VAR); and a group having three CES1 copies, in which the duplication, CES1A2, had increased transcriptional activity. Plasma concentrations of methylphenidate and its primary metabolites were determined at scheduled time points.

RESULTS

Median AUC of d-methylphenidate was significantly larger in the group carrying the 143E allele (53.3 ng ml^-1  h^-1 , range 38.6-93.9) than in the control group (21.4 ng ml^-1  h^-1 , range 15.7-34.9) (P < 0.0001). Median AUC of d-methylphenidate was significantly larger in the group with four CES1 copies (34.5 ng ml^-1  h^-1 , range 21.3-62.8) than in the control group (P = 0.01) and the group with three CES1 copies (23.8 ng ml^-1  h^-1 , range 15.3-32.0, P = 0.03). There was no difference between the groups with two and three copies of CES1.

CONCLUSIONS

The 143E allele resulted in an increased AUC, suggesting a significantly decreased CES1 enzyme activity. Surprisingly, this was also the case in subjects with homozygous duplication of CES1, perhaps reflecting an undiscovered mutation affecting the activity of the enzyme.

[Methylphenidate in the treatment of children with attention-deficit hyperactivity disorder: monitoring in biological matrices]

Attention-deficit hyperactivity disorder (ADHD) has emerged in the last few years as the most commonly diagnosed and treated psychiatric disorder in the paediatric population. In 1980's, methylphenidate (MFD) a psychomotor stimulant drug, was approved in Spain for the symptomatic therapy of ADHD. Since then, MFD has become one of the most extensively prescribed and studied treatment for ADHD both in children and adults. In this paper, the main pharmacological issues of MFD are reviewed, focusing on its pharmacokinetics in conventional (blood and urine) and non-conventional (hair, oral fluid and sweat) biological matrices, its pharmaceutical preparations, therapeutic levels and side effects.

An update on the pharmacotherapy of attention-deficit/hyperactivity disorder in adults

Adults with attention-deficit/hyperactivity disorder (ADHD) are more frequently presenting for diagnosis and treatment. Medication is considered to be appropriate among available treatments for ADHD; however, the evidence supporting the use of pharmacotherapeutics for adults with ADHD remains less established. In this article, the effectiveness and dosing parameters of the various agents investigated for adult ADHD are reviewed. In adults with ADHD, short-term improvements in symptomatology have been documented through the use of stimulants and antidepressants. Studies suggest that methylphenidate and amphetamine maintained an immediate onset of action, whereas the ADHD response to the nonstimulants appeared to be delayed. At a group level, there appears to be some, albeit not entirely consistent, dose-dependent responses to amphetamine and methylphenidate. Generally speaking, variability in diagnostic criteria, dosing parameters and response rates between the various studies was considerable, and most studies were of a relatively short duration. The aggregate literature shows that the stimulants and catecholaminergic nonstimulants investigated had a clinically significant beneficial effect on treating ADHD in adults.

Pharmacokinetic variability of long-acting stimulants in the treatment of children and adults with attention-deficit hyperactivity disorder

Methylphenidate- and amfetamine-based stimulants are first-line pharmacotherapies for attention-deficit hyperactivity disorder, a common neurobehavioural disorder in children and adults. A number of long-acting stimulant formulations have been developed with the aim of providing once-daily dosing, employing various means to extend duration of action, including a transdermal delivery system, an osmotic-release oral system, capsules with a mixture of immediate- and delayed-release beads, and prodrug technology. Coefficients of variance of pharmacokinetic measures can estimate the levels of pharmacokinetic variability based on the measurable variance between different individuals receiving the same dose of stimulant (interindividual variability) and within the same individual over multiple administrations (intraindividual variability). Differences in formulation clearly impact pharmacokinetic profiles. Many medications exhibit wide interindividual variability in clinical response. Stimulants with low levels of inter- and intraindividual variability may be better suited to provide consistent levels of medication to patients. The pharmacokinetic profile of stimulants using pH-dependent bead technology can vary depending on food consumption or concomitant administration of medications that alter gastric pH. While delivery of methylphenidate with the transdermal delivery system would be unaffected by gastrointestinal factors, intersubject variability is nonetheless substantial. Unlike the beaded formulations and, to some extent (when considering total exposure) the osmotic-release formulation, systemic exposure to amfetamine with the prodrug stimulant lisdexamfetamine dimesylate appears largely unaffected by such factors, likely owing to its dependence on systemic enzymatic cleavage of the precursor molecule, which occurs primarily in the blood involving red blood cells. The high capacity but as yet unidentified enzymatic system for conversion of lisdexamfetamine dimesylate may contribute to its consistent pharmacokinetic profile. The reasons underlying observed differential responses to stimulants are likely to be multifactorial, including pharmacodynamic factors. While the use of stimulants with low inter- and intrapatient pharmacokinetic variability does not obviate the need to titrate stimulant doses, stimulants with low intraindividual variation in pharmacokinetic parameters may reduce the likelihood of patients falling into subtherapeutic drug concentrations or reaching drug concentrations at which the risk of adverse events increases. As such, clinicians are urged both to adjust stimulant doses based on therapeutic response and the risk for adverse events and to monitor patients for potential causes of pharmacokinetic variability.

Psychopharmacology in pediatric critical care

Psychopharmacologic treatment in pediatric critical care requires a careful child or adolescent psychiatric evaluation, including a thorough review of the history of present illness or injury, any current or pre-existing psychiatric disorder, past history, and laboratory studies. Although there is limited evidence to guide psychopharmacologic practice in this setting, psychopharmacologic treatment is increasing in critical care, with known indications for treatment, benefits, and risks; initial dosing guidelines; and best practices. Treatment is guided by the knowledge bases in pediatric physiology, psycho-pharmacology, and treatment of critically ill adults. Pharmacologic considerations include pharmacokinetic and pharmcodynamic aspects of specific drugs and drug classes, in particular elimination half-life, developmental considerations, drug interactions, and adverse effects. Evaluation and management of pain is a key initial step, as pain may mimic psychiatric symptoms and its effective treatment can ameliorate them. Patient comfort and safety are primary objectives for children who are acutely ill and who will survive and for those who will not. Judicious use of psychopharmacolgic agents in pediatric critical care using the limited but growing evidence base and a clinical best practices collaborative approach can reduce anxiety,sadness, disorientation, and agitation; improve analgesia; and save lives of children who are suicidal or delirious. In addition to pain, other disorders or indications for psychopharmacologic treatment are affective disorders;PTSD; post-suicide attempt patients; disruptive behavior disorders (especially ADHD); and adjustment, developmental, and substance use disorders. Treating children who are critically ill with psychotropic drugs is an integral component of comprehensive pediatric critical care in relieving pain and delirium; reducing inattention or agitation or aggressive behavior;relieving acute stress, anxiety, or depression; and improving sleep and nutrition. In palliative care, psychopharmacology is integrated with psychologicapproaches to enhance children's comfort at the end of life. Defining how best to prevent the adverse consequences of suffering and stress in pediatric critical care is a goal for protocols and for new psychopharmacologic research [23,153].

[Pharmacological treatment in adults with attention deficit hyperactivity disorder]

Treatment in adults with attention deficit hyperactivity disorder predominantly relies on pharmacotherapeutic approaches especially with psychostimulants. Empirical studies indicate that their clinical effectiveness may be as high as in children and adolescents, especially in higher dosages. However, due to the high prevalence of comorbidities, e.g. depression, psychopharmacological treatment requires an extended use of other substance groups, especially antidepressants. An optimal treatment response necessitates the choice of an adequate substance depending on the leading clinical symptoms and a procedure of an individual titration of different dosages. This article reviews the current empirical results in the pharmacological treatment of ADHD in adults and provides possible treatment strategies for clinical practice.

Association of the 480 bp DAT1 allele with methylphenidate response in a sample of Irish children with ADHD

Several studies have implicated the dopamine transporter gene (DAT1) as conferring susceptibility to attention deficit hyperactivity disorder (ADHD), in particular, a VNTR situated at the 3' end of the gene. In addition, the 10-repeat VNTR allele associated with ADHD has been reported to be associated with an over-active transporter protein (DAT). Thus children possessing this variant might be particularly responsive to methylphenidate, a drug known to act by blocking DAT. We have examined this hypothesis and now report an association between the 10-repeat VNTR DAT1 polymorphism and retrospectively rated methylphenidate response in a sample of 119 Irish children with ADHD (chi(2) = 7.918, df = 1, P = 0.005). Our findings suggest a role for the 10-repeat DAT1 risk allele in medication response and may help to predict positive clinical outcome in ADHD.

Pharmacokinetics of methylphenidate after oral administration of two modified-release formulations in healthy adults

OBJECTIVE

To compare the rate and extent of absorption of DL-threo-methylphenidate (MPH) from two modified-release MPH formulations at their respective recommended starting doses in healthy adult volunteers.

DESIGN

Open-label, randomised, crossover, bioavailability study.

PARTICIPANTS

Twenty healthy adult male and female volunteers.

METHODS

Subjects received single doses of two modified-release formulations of MPH, a 20mg capsule (Ritalin) LA) and an 18 mg tablet (Concerta). A total of 19 plasma samples was collected over 24 hours, and MPH plasma concentrations were determined by liquid chromatography-mass spectrometry (LC-MS/MS). These values were used to calculate standard noncompartmental pharmacokinetic parameters describing the rate (peak concentration and time to peak concentration) and extent (area under the concentration-time curve, AUC) of absorption of the two formulations. The relative bioavailability of the two drugs was assessed using a 90% confidence interval, based on the lower and upper endpoints of the confidence interval for the ratios of the geometric means (log transformed) being within the 0.80-1.25 equivalence criterion.

RESULTS

Nineteen subjects, ten male and nine female, aged 21-34 years completed both treatment phases of the study. The Ritalin LA formulation displayed a distinctly biphasic pharmacokinetic profile, with mean initial peak plasma concentration of 7 microg/L at an average of 2.1 hours after administration and a second peak of 9.3 microg/L occurring at 5.6 hours. In contrast, the profile of the Concerta formulation rapidly reached an initial plateau concentration of 3.4 microg/L at 3.3 hours after administration and a second mean plateau concentration of 5.9 microg/L approximately 6 hours after administration. Substantially more MPH was absorbed from Ritalin LA than from Concert over the first 4 hours; the respective AUC(4) values were 18.5 and 9.3 microg x h/L (p < 0.001). The overall extent of absorption of MPH was similar between the two formulations. Oral clearance was identical between the two dosage forms.

CONCLUSIONS

The Ritalin LA formulation exhibited more rapid initial absorption and reached significantly higher peak plasma concentrations compared with the Concerta formulation, although the oral bioavailability of MPH was similar between the two formulations. The Ritalin LA capsule demonstrated a distinctly bimodal plasma concentration-time profile. MPH plasma concentrations resulting from Concerta reached a peak at 6 hours. These results indicate that the recommended starting dose of the Ritalin LA 20 mg capsule formulation provides more rapid absorption and higher peak plasma concentrations than the recommended 18 mg starting dose of the Concerta formulation.

Pharmacokinetic and pharmacodynamic properties of stimulants: implications for the design of new treatments for ADHD

In the USA, the stimulant drug methylphenidate (MPH) is used to treat a large number (2 million or more per year) of children with Attention Deficit Hyperactivity Disorder (ADHD). Although the US FDA approved MPH in the 1960s, the pharmacokinetic (PK) properties of serum concentrations of MPH in children with ADHD were not described until the 1980s, and then in only a few cases. Recently, information from drug development programs have increased our knowledge about the serum PK and some pharmacodynamic (PD) characteristics of MPH in ADHD children, and studies based on positron emission tomograpy (PET) in adult volunteers have provided new knowledge about the PK properties of MPH at the primary site of action in the brain. We will review these two topics and use this new information to evaluate the mechanisms of action of MPH.

A review of the pharmacotherapy of adults with attention-deficit/hyperactivity disorder

OBJECTIVE

Despite the increasing recognition of attention deficit hyperactivity disorder (ADHD) in adults, the use of pharmacotherapeutics remains less established.

METHODS

A systematic review of the literature identified 15 studies (N = 435 subjects) of stimulants, and 22 studies of non-stimulant medications (N = 421 subjects) including antidepressants, antihypertensives, amino acids, and wake-promoting agents for the treatment of ADHD in adults.

RESULTS

Studies with stimulants and antidepressants demonstrated significant short-term improvement in ADHD symptoms compared to placebo in adults. Methylphenidate (MPH) and amphetamine had an immediate onset of action whereas the ADHD response to pemoline and antidepressants appeared delayed. The response to amphetamine and MPH appears to be dose-dependent. Controlled data on nicotonic and noradrenergic compounds appear promising. There was considerable variability in diagnostic criteria, dosing parameters, and response rates between the various studies.

CONCLUSIONS

Under controlled conditions, the aggregate literature shows that the stimulants and noradrenergic antidepressants had a clinically and statistically significant beneficial effect on treating ADHD in adults.

A postmarketing clinical experience study of Metadate CD

OBJECTIVE

The objective of the study was to investigate the effectiveness and safety of Metadate CD (methylphenidate HCl, USP) Extended Release Capsules in the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD), in actual clinical practice.

METHOD

This was a multicenter, open-label, postmarketing study. Eligible patients were aged 6-17 with a diagnosis of ADHD and receiving either no treatment or maintenance treatment with another approved methylphenidate (MPH) product. Metadate CD was administered once daily for 3 weeks, titrated against reported and observed symptoms. Clinical Global Impression (CGI) scores at Week 3 were used for the primary efficacy evaluation. Patient treatment satisfaction was determined by questionnaire at the final evaluation visit. Safety was assessed through adverse event reporting, laboratory tests and vital sign measurements.

RESULTS

Overall, of the 308 patients in the Intent-To-Treat population, the majority (65%) demonstrated a positive response to Metadate CD (defined as CGI Global Improvement rating of very much or much improved). In addition, patients previously treated with immediate-release or extended-release tablet formulations of MPH were successfully converted to Metadate CD at a comparable dose. Most patients (87%) were very satisfied or moderately satisfied with study treatment, and among previously treated patients, 71% rated Metadate CD as much better or better than their previous MPH treatment. Adverse events were consistent with current FDA-approved product labeling for Metadate CD.

CONCLUSIONS

Metadate CD is effective and well-tolerated in actual clinical use for ADHD.

Single-dose pharmacokinetics of methylphenidate in CYP2D6 extensive and poor metabolizers

Six adults phenotyped as either extensive (N = 4) or poor (N = 2) metabolizers for cytochrome P450 (CYP) 2D6 were given a 10-mg oral dose of methylphenidate (MPH) on two separate occasions with and without quinidine, a potent CYP2D6 inhibitor. Quinidine had no significant effect on the pharmacokinetics of either MPH or ritalinic acid, its major metabolite, in either group of CYP2D6 metabolizers. These data suggest a lack of involvement of CYP2D6 in the metabolism of MPH. Drugs that are inhibitors of CYP2D6 when taken concurrently with MPH should not affect its plasma concentration.

Attention Deficit Hyperactivity Disorder (ADHD): Selected review of causes, comorbidity and treatment

A limited review of the causes, comorbidity, diagnosis and treatment is offered to emphasize the difficulties in diagnosing and treating Attention Deficit Hyperactivity Disorder and Hyperkinetic Disorder. Some of the difficulties include controversies about the existence of a separate disorder, the changes in symptoms with age, the short-lived improvement on medication and the claims of unsubstantiated treatments. This selected review should help the reader to consider recent findings in the aetiology, diagnosis and treatment of ADHD.

Acute mood improvement after dextroamphetamine and methylphenidate in narcolepsy

Mood changes following ingestion of dextroamphetamine (D-AMP) or methylphenidate (MPH) were examined in 40 narcoleptic patients. The Profile of Mood Status (POMS) and eight additional adjectives describing feelings were used to quantify changes in mood before taking stimulant medication and approximately 90 minutes after ingestion of medication. No significant differences were found between the effects of the two stimulants. When the data from D-AMP and MPH were combined, significantly higher ratings on the POMS factor of Vigour-Activity and the adjectives of 'confident', 'talkative' and 'competitive' were found. Lower ratings after medication were noted for the POMS factors of Fatigue-Inertia, Depression-Dejection and Confusion-Bewilderment (all P < 0.001). These effects are similar to those previously reported in normal subjects as well as in certain other patient populations. The findings indicate a possible therapeutic role of stimulant medication not only for the treatment of excessive sleepiness but also for improving affect, motor and mental vigour, and aspects of cognition.

Pharmacotherapy of adult attention deficit/hyperactivity disorder: a review

Adult attention deficit/hyperactivity disorder (ADHD) is an increasingly recognized disorder with associated psychiatric comorbidity and impairment. Although pharmacotherapy serves an important role in treating ADHD and other concurrent psychiatric disorders in children and adolescents, the use of pharmacotherapeutics for adults with ADHD remains less established. In this report, the effectiveness and dosing parameters of the various agents investigated for adult ADHD are reviewed. A systematic review of the available literature identified 7 studies (N = 193 subjects) of psychostimulants and 10 studies of nonstimulant medications (N = 167 subjects) including antidepressants, antihypertensives, and amino acids for the treatment of ADHD in adults. The majority of double-blind investigations were with the psychostimulants, with the nonstimulant agents, generally antidepressants, studied under open conditions. There was considerable variability in diagnostic criteria, dosing parameters, and response rates between the various studies. Under controlled conditions, the aggregate literature shows that the stimulants had a clinically and statistically significant effect on reducing ADHD symptoms. Open studies on the nonserotonergic antidepressants (tricyclics, bupropion, and monoamine oxidase inhibitors) also show a moderate anti-ADHD effect. The literature appears to support the use of robust doses of both stimulants and antidepressants for ADHD in adults. Further controlled studies applying stringent diagnostic criteria and outcome methodology are necessary to define the range of pharmacotherapeutic options for adults with ADHD.

The use of methylphenidate for cognitive decline associated with HIV disease

OBJECTIVE

Complaints of cognitive changes are often expressed by patients at all stages of HIV infection. Such changes include decreased memory and attention span, diminished concentration, apathy, and "slowing." Methylphenidate (MPD) has been used in several clinical studies in men with late-stage HIV disease in an attempt to ameliorate these difficulties. The objectives of this review article are to review salient psychopharmacological characteristics of MPD and to describe the research and clinical literature supporting the use of MPD in patients at all stages of HIV infection.

METHODS

Seven studies, case reports, or abstracts from International Conferences on AIDS were available in the English literature through August, 1993, directly addressing the use of MPD in patients with HIV disease. Twenty-nine papers were reviewed for pharmacokinetic data, eighteen for safety and side effects issues, and seventeen for relevant contributions from the neuropsychological testing literature.

RESULTS

Studies in clinical settings have used doses ranges from 10-90 mg. per day in two or three divided doses with reportedly good results in improving both affective and cognitive symptoms associated with HIV disease. Side effects have been relatively mild and patient satisfaction with treatment has been high. However, no studies have been conducted in early stage HIV disease, where a significant minority of patients have similar complaints in the absence of clinically apparent immunosuppression. Likewise, placebo-controlled, dose-finding studies in AIDS patients are entirely lacking, and no studies in women with HIV disease and cognitive changes have been published.

CONCLUSIONS

In spite of these important research short-comings, clinical experience with MPD treatment of cognitive changes in men with HIV/AIDS is consistent with the notion that this medication holds significant promise to improve the quality of life for persons living with HIV/AIDS. Controlled studies to test this hypothesis are warranted.

Nonlinear kinetics of threo-methylphenidate enantiomers in a patient with narcolepsy and in healthy volunteers

We have studied the pharmacokinetics of methylphenidate enantiomers after the oral administration of different doses of racemic methylphenidate to one patient with narcolepsy and to four healthy volunteers. The plasma concentrations of (+)-methylphenidate were much higher than those of (-)-methylphenidate after each dose in all subjects. In the patient the oral clearance (CL/f) of (+)-methylphenidate fell 3-fold and the area under the concentration-time curve (AUC) rose 7-fold when the dose was increased from 20 to 40 mg (from 0.27 to 0.53 mg.kg-1), in spite of the relatively constant terminal half-life of 2.6-2.7 h. Similar dose-dependency was also observed in the healthy volunteers in the dose range of 10-60 mg (0.12-0.77 mg.kg-1). The mean value of CL/f for the 40 mg dose was significantly lower than that for the 20 mg dose. The mean AUC of the (+)-isomer corrected to a dose of 10 mg increased significantly between the 20 mg and 40 mg doses. In the urine (+)- and (-)-ritalinic acid were excreted for 48 h after each dose as 32-37% and 34-40% of the dose respectively. The mean total recoveries (sum of enantiomers of methylphenidate and its metabolite, ritalinic acid) in the urine were relatively constant (63-78% of the doses), suggesting that the changes in AUC with dose may not be due to a change in the intestinal absorption of racemic methylphenidate. We conclude that the nonlinear kinetics of (+)-methylphenidate may be due to saturation of its presystemic elimination.

Pharmacodynamics of pemoline in attention deficit disorder with hyperactivity

The onset, duration, and offset of pemoline action to improve cognitive performance is examined intensively in 25 prepubescent males suffering from attention-deficit disorder with hyperactivity (ADDH). The purpose was to characterize the pharmacodynamics of pemoline in ADDH patients through correlation of plasma pemoline concentration with psychometric measures of memory search efficiency and paired-associates learning, with the physiological effect of pemoline on dopaminergic transmission concurrently measured by analysis of plasma prolactin response. The effect of pemoline on neuroprocessing is apparent within the first 2 hours after administration with an inverse relationship between plasma pemoline and prolactin concentration present at hour one only (r = 0.84; p = 0.005). Pemoline therapy for 3 weeks does not significantly affect area under the curve for pemoline or prolactin nor did the effect on memory search efficiency decrease, suggesting no apparent tolerance.

Treatment of attention deficit hyperactivity disorder: a critical review

This review evaluates the treatment of attention deficit hyperactivity disorder. Current evidence supports the belief that stimulants are the most effective and least toxic of the drugs used in the treatment of hyperactivity. Tricyclic antidepressants (TCAs), however, are preferable in subpopulations with concomitant anxiety or depressive disorders. Studies comparing stimulants with TCAs are evaluated and studies that have examined other antidepressants are summarized. In addition, TCAs and stimulants are compared according to adverse-effect profiles, pharmacokinetic properties, and subgroup responses. Based on these data and the recently reported sudden deaths in children receiving desipramine, treatment recommendations are made.

Enantioselective aspects of the disposition of dl-threo-methylphenidate after the administration of a sustained-release formulation to children with attention deficit-hyperactivity disorder

It has been shown previously that immediate-release dl-threo-methylphenidate (Ritalin) undergoes stereoselective disposition in human adults as well as in children with attention deficit-hyperactivity disorder. Although the sustained-release formulation of dl-threo-methylphenidate (Ritalin-SR) has been demonstrated to be effective in sustaining the attention of the children with attention deficit-hyperactivity disorder, there are no data on plasma levels of methylphenidate after administration of the sustained-release formulation. The purpose of this present investigation was twofold: (1) to determine whether the levels of methylphenidate were sustained for over a time period of 8 h, and (2) to examine enantioselective aspects of the pharmacokinetics following the ingestion of the sustained-release formulation. Six children with attention deficit-hyperactivity disorder were given 20 mg of sustained-release dl-threo methylphenidate. Plasma samples were harvested for a period up to 12 h following ingestion of the drug. The levels of both the enantiomers were sustained for a period of 8 h (the plasma levels of d-methylphenidate were 8- to 10-fold higher than those of the l-enantiomer in the profiles of all six children). Mean areas under the plasma level time curves were 132.78 +/- 92.47 ng.h/mL for d-methylphenidate and 12.73 +/- 7.37 ng.h/mL for l-methylphenidate. The values of oral clearance and apparent volume of distribution calculated for l-enantiomer were higher than the corresponding values for the d-antipode.

Sustained release methylphenidate: pharmacokinetic studies in ADDH males

Methylphenidate is widely used in the treatment of school-age children with attention deficit disorder with hyperactivity (ADDH). It is available in a short-acting (MPH) and a long-acting (MPH-SR) preparation. Nine males with ADDH participated in a 1-day pharmacokinetic study following a single morning dose of 20 mg. MPH-SR. Data are presented on MPH-SR's half-life (T 1/2), peak concentrations achieved (Cmax) and the time to the peak plasma concentrations (Tmax). Similar data were gathered from a second group of eight ADDH males treated with a higher, single morning dose of standard, short-acting MPH. After adjusting for dose differences, comparisons of the two sets of plasma concentration curves suggest that MPH-SR has a longer Tmax, but that it does not reach the same Cmax as an identical dose of standard MPH.

Methylphenidate affects strategic choice behavior in normal adult humans

The time course of serum concentration and performance on a concurrent probability matching task were evaluated in normal adults receiving 0.15 or 0.3 mg/kg of methylphenidate. The behavioral task, an arcade-like problem-solving game, revealed that drug-treated subjects improved their performance upon repeated testings during pharmacokinetic evaluation at a lower rate than did non-treated controls over the same time span. However, drug-treated subjects failed to adopt the adaptive problem-solving strategies selected by controls.

Development of enantioselective gas chromatographic quantitation assay for dl-threo-methylphenidate in biological fluids

An enantioselective gas chromatographic quantitation assay was developed for the enantiomers of dl-threo-methylphenidate in plasma and urine. dl-threo-Methylphenidate and the internal standard were acylated with N-heptafluorobutyryl-1-prolylchloride under Schotten-Baumann conditions prior to gas chromatographic separation on achiral mixed stationary phases. The derivatives were detected by means of a nitrogen-phosphorus detector. Linear and reproducible calibration curves were obtained over the concentration ranges 0.43-43.25 and 2.16-216.25 ng/ml enantiomer in plasma or urine, respectively. This enantioselective gas chromatographic quantitation assay was applied in a single oral dose disposition study of dl-threo-methylphenidate in a healthy adult volunteer. Stereoselective differences were observed in the plasma concentration-time profiles and cumulative urinary excretion profiles following oral doses of 20 and 40 mg of dl-threo-methylphenidate hydrochloride. Only d-threo-methylphenidate was detectable in plasma after 4 h.

Gas chromatographic-mass spectrometric analysis of methylphenidate and p-hydroxymethylphenidate using deuterated internal standards

A gas chromatography-mass spectrometry assay is described for the simultaneous determination of threo-dl-methylphenidate and threo-dl-p-hydroxymethylphenidate in plasma and urine using selected ion monitoring of electron impact generated fragments of their pentafluoropropionyl derivatives. The use of recently available deuterated analogues as internal standards improves overall performance relative to previous methods. The practical limit of quantifiable detection of the assay is 0.5 ng/ml for both methylphenidate and p-hydroxymethylphenidate. p-Hydroxymethylphenidate appears to be a significant urinary metabolite of methylphenidate in rats but not in humans.