NTP-CERHR Expert Panel Report on the reproductive and developmental toxicity of methylphenidate

Physiologically-Based Pharmacokinetic Modeling to Predict Methylphenidate Exposure Affected by Interplay Among Carboxylesterase 1 Pharmacogenetics, Drug-Drug Interactions, and Sex

BACKGROUND AND OBJECTIVE

The pharmacokinetics (PK) of methylphenidate (MPH) differ significantly among individuals. Carboxylesterase 1 (CES1) is the primary enzyme metabolizing MPH, and its function is affected by genetic variants, drug-drug interaction (DDI), and sex. The object of this study is to evaluate CES1 pharmacogenetics as related to MPH metabolism using human liver samples and develop a physiologically-based pharmacokinetic (PBPK) modeling approach to investigate the influence of CES1 genotypes and other factors on MPH PK.

METHODS

The effect of the CES1 variant G143E (rs71647871) on MPH metabolism was studied utilizing 102 individual human liver S9 (HLS9) fraction samples. PBPK models were developed using the population-based PBPK software PK-Sim® by incorporating the HLS9 incubation data. The established models were applied to simulate MPH PK profiles under various clinical scenarios, including different genotypes, drug-alcohol interactions, and the difference between males and females.

RESULTS

The HLS9 incubation study showed that subjects heterozygous for the CES1 variant G143E metabolized MPH at a rate of approximately 50% of that in non-carriers. The developed PBPK models successfully predicted the exposure alteration of MPH from the G143E genetic variant, ethanol-MPH DDI, and sex. Importantly, the study suggests that male G143E carriers who are alcohol consumers are at a higher risk of MPH overexposure.

CONCLUSION

PBPK modeling provides a means for better understanding the mechanisms underlying interindividual variability in MPH PK and PD and could be utilized to develop a safer and more effective MPH pharmacotherapy regimen.

Effects of Chronic Use of Methylphenidate on Spermatogenesis and Sexual Hormones in Adult Male Rats

Background: The growing prevalence of Attention Deficit Hyperactivity Disorder (ADHD) and the non-medical use of Methylphenidate (MPH) among the youth have lead male infertility to be a major health problem. Objectives: The present study was conducted to investigate the impacts of MPH administration on different aspects of productivity, including total body weight, testis weight, spermatogenesis, sperm motility, histopathology changes, and sex hormone serum levels in male rats. Methods: This study was performed with 54 eight-week-old male rats divided into one control and two experimental groups. The experimental groups were gavaged with 2 and 10 mg/kg methylphenidate daily while the control group was gavaged with normal saline (at the same dosage). After 60 days, rats were subjected to blood sampling and bilateral orchidoepididymectomy under anesthesia. Spermogram, histological, and hormonal evaluations were performed on the samples. Testes weight and total body weight were also recorded. Results: The results revealed significant differences between the MPH and experimental groups in terms of hormonal, spermographic, and histopathologic features, as well as weight. Luteinizing hormone and testosterone levels, sperm count and motility, Leydig cell hyperplasia, spermatogenesis, congestion and necrosis levels, total body weight, and testis weight were significantly different between the experimental and control groups. However, no difference was observed between the experimental and control groups concerning follicle-stimulating hormone, maturation arrest, and edema levels. Conclusions: Based on the findings, MPH exposure exerts a significant effect on the testis and total body weight, as well as hormonal, spermatographic, and histopathologic characteristics. Accordingly, the present study provided an insight into the negative impression of MPH on sexual parameters.

The relationship between motor skills, ADHD symptoms, and childhood body weight

BACKGROUND

Research has suggested an important association between motor proficiency and overweight/obesity. Many children with motor difficulties experience ADHD symptoms which have also been linked with overweight/obesity. Previous research has not considered both ADHD and motor performance when investigating their relationship with overweight/obesity.

AIMS

To investigate the relationships between motor performance, ADHD symptoms, and overweight/obesity in children.

METHODS AND PROCEDURES

A cross-sectional study was conducted involving189 children aged six to 10 years. Symptoms of ADHD were identified using the SNAP-IV rating scale. Motor impairment (MI) was identified using the Movement Battery Assessment for Children-2. Body composition was estimated from the Body Mass Index (BMI) based on World Health Organization child growth standards.

OUTCOMES AND RESULTS

Balance was the only motor skill associated with BMI even after controlling for gender and ADHD. Group comparisons revealed that the proportion of overweight ADHD children was significantly less than the proportion of overweight control children and overweight MI children; the proportion of underweight ADHD children was significantly greater than the proportion of underweight MI children.

CONCLUSIONS AND IMPLICATIONS

The results highlight the importance of taking into consideration both ADHD symptoms and motor difficulties in the assessment and intervention of physical health outcomes in children with ADHD and/or movement problems.

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.

Effect of extended-release dexmethylphenidate and mixed amphetamine salts on sleep: a double-blind, randomized, crossover study in youth with attention-deficit hyperactivity disorder

OBJECTIVE

We sought to determine the dose-response effects of extended-release (ER) dexmethylphenidate (d-MPH) and ER mixed amphetamine salts (MAS) on objective measures of sleep.

METHODS

This was an 8-week, double-blind, placebo-controlled, randomized, two period, crossover study of youth with attention-deficit hyperactivity disorder (ADHD) as confirmed by the Kiddie Schedule for Affective Disorders for School-Age Children-Present and Lifetime version (K-SADS-PL). Children aged 10-17 years were recruited from clinical practice, colleague referrals, and flyers. Participants were randomized to initially receive either d-MPH or MAS. During each 4-week drug period, children received three dose levels (10, 20, and 25/30 mg) in ascending order, with placebo substituted for active medication in a randomized fashion during 1 week of the study. After 4 weeks, participants were switched to the alternative medication for another 4 weeks of treatment. The main outcome measure was sleep duration as measured by actigraphy. Children, parents, and researchers were blinded to drug, dose, and placebo status.

RESULTS

Sixty-five participants met the inclusion criteria and were enrolled in the study. Of these, 37 participants with sufficient sleep data for analysis were included. Sleep schedule measures showed a significant effect for dose on sleep start time (F(1,36) = 6.284; p < 0.05), with a significantly later sleep start time when children were receiving 20- or 30-mg doses, compared with placebo (p < 0.05). A significant dose effect was found on actual sleep duration (F(1,36) = 8.112; p < 0.05), with significantly shorter actual sleep duration for subjects receiving 30 mg compared with those receiving placebo (p < 0.05). There were no significant differences on sleep duration or sleep schedule between the two stimulant medications. The trial is complete and closed to follow-up.

CONCLUSIONS

Higher stimulant doses were associated with reduced sleep duration and later sleep start times, regardless of medication class.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00393042.

Effects of developmental methylphenidate (MPH) treatment on monoamine neurochemistry of male and female rats

Attention Deficit Hyperactivity Disorder (ADHD) is estimated to affect 4-5% of the adult human population (Kessler et al., 2006; Willcutt, 2012). Often prescribed to attenuate ADHD symptoms (Nair and Moss, 2009), methylphenidate hydrochloride (MPH) can have substantial positive effects. However, there is a paucity of literature regarding its use during pregnancy. Thus, adult women with ADHD face a difficult decision when contemplating pregnancy. In this study, pregnant Sprague-Dawley rats were orally treated a total of 0 (water), 6 (low), 18 (medium), or 42 (high) mg MPH/kg body weight/day (divided into three doses) on gestational days 6-21 (i.e., the low dose received 2 mg MPH/kg body weight 3×/day). Offspring were orally treated with the same daily dose as their dam (divided into two doses) on postnatal days (PNDs) 1-21. One offspring/sex/litter was sacrificed at PND 22 or PND 104 (n=6-7/age/sex/treatment group) and the striatum was quickly dissected and frozen. High Performance Liquid Chromatography (HPLC) coupled to a Photo Diode Array detector (PDA) was used to analyze monoamine content in the striatum of one side while a sandwich ELISA was used to analyze tyrosine hydroxylase (TH) from the other side. Age significantly affected monoamine and metabolite content as well as turnover ratios (i.e., DA, DOPAC, HVA, DOPAC/DA, HVA/DA, 5-HT and 5-HIAA); however, there were no significant effects of sex. Adult rats of the low MPH group had higher DA levels than control adults (p<0.05). At both ages, subjects of the low MPH group had higher TH levels than controls (p<0.05), although neither effect (i.e., higher DA or TH levels) exhibited an apparent dose-response. PND 22 subjects of the high MPH treatment group had higher ratios of HVA/DA and DOPAC/DA than same-age control subjects (p<0.05). The increased TH levels of the low MPH group may be related to the increased DA levels of adult rats. While developmental MPH treatment appears to have some effects on monoamine system development, further studies are required to determine if these alterations manifest as functional changes in behavior.

Neonatal methylphenidate does not impair adult spatial learning in the Morris water maze in rats

Methylphenidate (MPD) is the most prescribed drug for attention deficit hyperactivity disorder. Licit and illicit use also occurs during pregnancy, however the effects from this use on offspring development are unknown. To model late gestational exposure, Sprague-Dawley litters were treated with 0, 5, 10, 20, or 30mg/kg×4/day every 2h with MPD on postnatal days 11-20 (within-litter design; days chosen to be comparable to human third trimester brain development). During treatment, body weights were decreased in MPD-treated groups; weight recovery occurred in all but the MPD-30 group by start of testing. MPD-treated rats showed no changes in anxiety (elevated zero maze), swimming ability (straight channel swimming), or spatial learning/reference memory (Morris water maze). MPD does not appear to pose a risk to these CNS functions after exposure during a stage of rat development analogous to third trimester human brain development.

Management of attention-deficit hyperactivity disorder in adults: focus on methylphenidate hydrochloride

Attention-deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders in young adults and causes significant psychosocial impairment and economic burden to society. Because of the paucity of long-term evidence and lack of national guidelines for diagnosis and management of adult ADHD, most of the data are based on experience derived from management of childhood ADHD. This article reviews the current evidence for the diagnosis and management of adult ADHD with special emphasis on the role of methylphenidate hydrochloride preparations in its treatment. Methylphenidate hydrochloride, a stimulant that acts through the dopaminergic and adrenergic pathways, has shown more than 75% efficacy in controlling the symptoms of adult ADHD. Although concern for diversion of the drug exists, recent data have shown benefits in preventing substance use disorders in patients with adult ADHD.

Attention Deficit/Hyperactivity Disorder in Adults

Attention deficit/hyperactivity disorder (ADHD), characterized by inattention, hyperactivity/impulsivity, or a combination of these, is being increasingly recognized in adults. Adult ADHD prevalence rates range from 1% to 4%. The pathophysiology of adult ADHD is likely multifactorial, including genetic, environmental, and neurobiological influences. Though ADHD diagnostic criteria per the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) were developed based on child samples, the symptoms are believed to be similar in adults, with some developmental differences in symptom presentation. This article identifies common presenting complaints of adults who have ADHD and provides information useful for differential diagnosis of these patients. Specific strategies for pharmacological and nonpharmacological intervention are also presented.