Dose-Proportional Pharmacokinetics ofd-threo-Methylphenidate After a Repeated-Action Release Dosage Form

An update on the pharmacokinetic considerations in the treatment of ADHD with long-acting methylphenidate and amphetamine formulations

Introduction: Long-acting stimulant formulations are recommended as first-line pharmacotherapy for attention-deficit/hyperactivity disorder (ADHD). Over the past 20 years, extended-release (ER) methylphenidate (MPH) and amphetamine (AMP) formulations have evolved to include varying drug delivery technologies, enantiomers/salts, and dosage forms. All formulations are characterized by a unique pharmacokinetic profile that is closely mirrored by pharmacodynamic response allowing clinicians to individualize therapy based on their patient's clinical needs and dosing preferences.Areas covered: This review provides an update on the pharmacokinetic properties of approved and investigational ER MPH and AMP formulations and highlights pharmacokinetic features that clinicians should consider when selecting a long-acting stimulant.Expert opinion: Since there are no reliable biomarkers that can predict individualized response to long-acting stimulants, clinicians need to consider their distinctive pharmacokinetic properties, including the pharmacokinetic profile, rate and extent of absorption, variability, dose proportionality, bioequivalence, and potential for accumulation. Clinicians also need to understand that certain factors can contribute to increased variability in pharmacokinetics and potentially affect outcomes. Less invasive, high-throughput techniques and novel time-based scales are being developed to advance research on the pharmacokinetic-pharmacodynamic relationships of stimulants. Model-based pharmacokinetic-pharmacodynamic approaches can be applied to aid the development of novel formulations and individualize therapy with existing drugs.

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.

A double-blind, randomized, placebo/active controlled crossover evaluation of the efficacy and safety of Ritalin ® LA in children with attention-deficit/hyperactivity disorder in a laboratory classroom setting

OBJECTIVES

The primary objective of this study was to demonstrate efficacy of Ritalin(®) LA 20 mg by showing superiority to placebo and noninferiority to Medikinet(®) Retard in a laboratory classroom setting. Secondary objectives included safety/tolerability and further efficacy parameters.

METHODS

A total of 147 children with attention-deficit/hyperactivity disorder (ADHD) diagnosed by the Kiddie Schedule for Affective Disorders and Schizophrenia (K-SADS) and aged 6-14 (81% males) and known to be methylphenidate (MPH) responders were enrolled in this multicenter, double-blind, randomized, placebo/active-controlled, three-period (7 days each) crossover study. The Swanson, Kotlin, Agler, M-Flynn, and Pelham (SKAMP) scale was used for efficacy ratings. The mean of SKAMP Combined ratings performed at 10:30 a.m., at 12:00 a.m., and at 1:30 p.m. was defined as the primary parameter.

RESULTS

In all, 146 patients completed all treatment periods. Intensity and frequency of adverse events were comparable between the two formulations. Ritalin(®) LA demonstrated superiority compared to placebo (p<0.0001). The observed difference in the SKAMP scores between Ritalin(®) LA and Medikinet(®) Retard between the hours 1.5 until 4.5 did not exceed the noninferiority margin (p=0.0003); therefore, the difference is regarded as not clinically relevant. Similar results were obtained for the secondary efficacy variables.

CONCLUSION

Ritalin(®) LA is an efficacious, well-tolerated treatment option for children aged 6-14 with ADHD.

Dexmethylphenidate extended release: a review of its use in the treatment of attention-deficit hyperactivity disorder

Dexmethylphenidate extended release (XR) [Focalin XR] is a CNS stimulant indicated for the treatment of attention-deficit hyperactivity disorder (ADHD) in patients aged > or = 6 years. Dexmethylphenidate contains the d-threo-enantiomer of methylphenidate. Dexmethylphenidate XR capsules have a bimodal release profile, which mimics two doses of dexmethylphenidate immediate release (IR) given 4 hours apart, and allows once-daily administration. Once-daily dexmethylphenidate XR was effective and generally well tolerated in the treatment of ADHD in children, adolescents and adults in placebo-controlled trials. Improvements in ADHD symptoms were significantly greater for dexmethylphenidate XR versus placebo throughout the day, from as early as 0.5 hours after drug administration up to 11-12 hours after administration. Furthermore, dexmethylphenidate XR showed greater efficacy than osmotic release oral system (OROS) methylphenidate over the first half of the laboratory classroom day in crossover trials; however, assessments late in the day (10-12 hours post-dose) favoured OROS methylphenidate. The once-daily administration regimen with dexmethylphenidate XR avoids the need for a midday dose to be administered at school; administration options are extended in that the contents of the dexmethylphenidate XR capsule can be sprinkled on apple sauce for patients unable to swallow the capsule whole. Although dexmethylphenidate XR is a controlled substance in the US, this formulation appears to have a low risk of abuse or misuse. Thus, dexmethylphenidate XR extends the range of first-line pharmacological treatment options for children, adolescents or adults with ADHD, particularly for patients who require a rapid onset and prolonged duration of action, including children who require a reduction in ADHD symptoms throughout the school day.