Sustained release methylphenidate: pharmacokinetic studies in ADDH males

Model-Based Approach for Establishing the Predicted Clinical Response of a Delayed-Release and Extended-Release Methylphenidate for the Treatment of Attention-Deficit/Hyperactivity Disorder

PURPOSE/BACKGROUND

HLD200 is an evening-dosed, delayed-release and extended-release methylphenidate (DR/ER-MPH) that provides a consistent delay in initial drug release to target onset of therapeutic effect from awakening and maintain it into the evening. Building on a modeling framework established with other extended-release methylphenidate formulations, pharmacokinetic (PK) and PK/pharmacodynamic (PD) models for DR/ER-MPH were developed to describe the time course of effect in response to a range of doses and administration times.

METHODS/PROCEDURES

Using available PK data from healthy adults, a population PK model was developed using a 1-compartment model with a time-varying absorption rate described by a single Weibull function. A PK/PD model was then developed using Swanson, Kotkin, Agler, M-Flynn, and Pelham combined scores from a phase 3 trial of children with attention-deficit/hyperactivity disorder and simulated plasma concentration-time data. Simulations using the PK/PD model were performed for doses of 60, 80, and 100 mg of DR/ER-MPH, administered 4 to 14 hours before the classroom day.

FINDINGS/RESULTS

The PK/PD model predicts that DR/ER-MPH produces a clinical response from early morning into the late afternoon or evening, with increased duration of response occurring with increasing doses. Furthermore, the PK/PD model predicts that maximal clinical effect is achieved with DR/ER-MPH administered 12 hours before the start of the classroom day.

IMPLICATIONS/CONCLUSIONS

Model-predicted duration of benefit with DR/ER-MPH is consistent with trial data documenting improvements in functional impairment during the early morning and evening. This model may facilitate dosage optimization by predicting changes in clinical benefit with dose and administration time adjustment.

Single-Dose Pharmacokinetics of HLD200, a Delayed-Release and Extended-Release Methylphenidate Formulation, in Healthy Adults and in Adolescents and Children with Attention-Deficit/Hyperactivity Disorder

OBJECTIVE

Current extended-release (ER) formulations of psychostimulants used for treatment of attention-deficit/hyperactivity disorder (ADHD) provide an extended duration of ADHD symptom control; however, the onset of efficacy can be protracted and variable, leaving the early morning untreated. The primary objective was to characterize the single-dose pharmacokinetics and tolerability of HLD200, an evening-dosed, delayed-release (DR) and ER formulation of methylphenidate (MPH), in healthy adults and in adolescents and children with ADHD.

METHODS

The pharmacokinetics and tolerability of a single, oral evening dose of HLD200 (54 mg) were evaluated in two single-center open-label studies: the first in healthy adults (n = 12) and the second in adolescents (n = 18) and children (n = 11) with ADHD. Primary pharmacokinetic endpoints were the rate and extent of MPH absorption (C_max and area under the curve [AUC]) and time to peak concentration (T_max). These parameters were calculated using noncompartmental analysis.

RESULTS

HLD200 produced a pharmacokinetic profile characterized by an 8- to 10-hour delay in MPH release, followed by a period of extended controlled release, resulting in an ascending absorption profile that coincided with the early morning and afternoon. Mean values (coefficient of variation [CV]%) of weight-adjusted pharmacokinetic parameters were similar in adults and in adolescents and children with ADHD: C_max ([ng/mL]/[mg/kg]) was 9.1 (35.2), 8.8 (34.5), and 7.4 (30.1); AUC_0-t ([ng · h/mL]/[mg/kg]) was 126.5 (35.5), 129.4 (34.8), and 129.7 (27.3); and T_max (hours) was 15.6 (11.1), 17.1 (14.5), and 17.7 (14.1), respectively. Intersubject variability in the mean time to achieve ascending plasma MPH concentrations of 2, 3, 4, and 5 ng/mL was low (CV: 7.8%-17.7%).

CONCLUSIONS

Evening-dosed HLD200 produces the intended DR and ER pharmacokinetic profile that provides a consistent predictable delay in initial MPH release until the early morning, followed by extended release across the day. The body weight-adjusted pharmacokinetics of HLD200 were similar between adults and adolescents and children with ADHD.

Beyond the pill: new medication delivery options for ADHD

Successful treatment of pediatric disorders has necessitated the development of alternative medication formulations, as children may prefer alternative dosage forms to tablets or capsules. This is especially true for attention-deficit/hyperactivity disorder (ADHD), which is one of the most common chronic pediatric conditions and often involves children with a variety of overlapping physical, psychological, or neurodevelopmental disorders. A special challenge for developing alternative dosage forms for ADHD treatment is the incorporation of a once-daily long-acting formulation. Traditional ADHD medication formulations have been limited, and issues surrounding prescribed dosing regimens-including poor medication adherence, difficulty swallowing, and the lack of dosing titration options-persist in ADHD treatment. In other disease areas, the development of alternative formulations has provided options for patients who have issues with consuming solid dosage forms, particularly children and individuals with developmental disorders. In the light of these new developments, several alternative formulations for ADHD medications are under development or have recently become available. This article reviews the various strategies for developing alternative dosage forms in other disease areas and discusses the application of these strategies in ADHD treatment. Alternative dosage forms may increase medication adherence, compliance, and patient preference and, therefore, improve the overall treatment for ADHD.

Methylphenidate on Cognitive Improvement in Patients with Traumatic Brain Injury: A Meta-Analysis

Although methylphenidate has been used as a neurostimulant to treat patients with attention deficit hyperactivity disorder, its therapeutic role in the psychomotor or cognitive recovery of patients with traumatic brain injuries (TBIs) in both intensive care and rehabilitation settings has not been adequately explored. To address this issue, this meta-analysis searched the available electronic databases using the key words “methylphenidate”, “brain injuries”, “head injuries”, and “traumatic brain injury”. Analysis of the ten double-blind RCTs demonstrated significant benefit in using methylphenidate for enhancing vigilance-associated attention (i.e., selective, sustained, and divided attention) in patients with TBIs (standardized mean difference: 0.45, 95% CI: 0.10 to 0.79), especially in sustained attention (standardized mean difference: 0.66, 95% CI: 0.22 to 1.10). However, no significant positive impact was noted on the facilitation of memory or processing speed. More studies on the efficacy and safety of methylphenidate for the cognitive improvement of patients with TBIs are warranted.

Methylphenidate: established and expanding roles in symptom management

Methylphenidate is a psychostimulant originally used for the treatment of attention-deficit disorder. Methylphenidate inhibits neuronal neurotransmitter transporters involved in the uptake of dopamine and norepinephrine at the level of the synapse. Inhibition of these transmitter transporters leads to increased concentrations of dopamine and norepinephrine in the synapse, which results in increasing alertness. The stimulant effect of methylphenidate has been used for the treatment of major depression, poststroke depression, cognitive enhancement in patients with brain tumors, neurodegenerative disorders, HIV disease, fatigue, and as a treatment for delirium and sedation associated with opioid use. Other areas where methylphenidate has been evaluated include gait disorders in the elderly individuals and the treatment of apathy in dementia. Analgesic effects have been demonstrated in preclinical models but true analgesic effects remain to be proven in humans. This article reviews the current use of methylphenidate for symptom management with a critical look at the evidence base for its efficacy in the conditions described.

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.

Evolution of stimulants to treat ADHD: transdermal methylphenidate

OBJECTIVE

The following comprehensive review describes the evolution of stimulant drug formulations used in the treatment of attention-deficit/hyperactivity disorder (ADHD). Emphasis is placed on the basic and clinical pharmacology of the dl-methylphenidate (MPH) transdermal system (MTS).

METHODS

The pharmacokinetic and pharmacodynamic literature pertaining to MPH and amphetamine enantiomers was reviewed in the context of ADHD therapy and MTS as a treatment option.

RESULTS

MTS incorporates MPH into an adhesive monolithic matrix, using the free base form of the drug to facilitate transdermal absorption. MTS technology minimizes contact dermatitis by eliminating to need for percutaneous penetration enhancers. After a lag time of approximately 2 h, plasma concentrations of the therapeutic d-MPH isomer become detectable, then continuously rise over the course of the recommended 9 h wear time. Concentrations of l-MPH typically attain 40-50% that of d-MPH (vs. 1-2% following oral MPH). Unauthorized MTS removal poses some misuse liability and over 50% of MTS drug content remains in the discarded system.

CONCLUSIONS

While liquid or chewable MPH formulations overcome potential swallowing difficulties, as do sprinkled once-daily extended-release (ER) MPH products, only MTS addresses swallowing difficulties while also offering a flexible individualized MPH exposure time in a once-daily MPH regimen.

New methylphenidate formulations for the treatment of attention-deficit/hyperactivity disorder

dl-Methylphenidate (MPH) remains the most widely used pharmacological agent in the treatment of attention-deficit/hyperactivity disorder (ADHD). The predominantly dopaminergic mechanism of the psychostimulant actions has become more clearly defined. Neuroimaging and genetic studies are revealing the underlying neuropathology in ADHD. Novel extended-release (ER) MPH formulations now offer drug delivery options to overcome both the short-term actions of immediate-release (IR) MPH and the acute tolerance associated with the first-generation ER-MPH products. These novel MPH products apply proprietary technologies such as OROS (Alza), Diffucaps (Eurand) and SODAS (Elan) to offer both the convenience of once-a-day administration and absorption profiles resembling, to varying degrees, the standard multiple dose schedules of IR-MPH. The pharmacodynamics of the separate MPH enantiomers is in the process of further neuropharmacological characterisation. It is well established that dl-MPH undergoes marked stereoselective metabolism. Although l-MPH exhibits only minimal oral absorption, it may preferentially penetrate the brain, and interacts with ethanol to form the metabolite ethylphenidate. The newly approved resolved enantiomer product d-MPH is now available in an IR formulation, and when administered at one-half the dose to that of the racemate, is purported to produce a longer duration of clinical effect, despite essentially identical pharmacokinetics. A long-acting formulation of d-MPH, which employs the SODAS technology, is in the advanced stages of clinical development.

The science of stimulant abuse

Stimulant medications, although classified by the US Drug Enforcement Agency as controlled with a Schedule IIa rating, are ubiquitous in our society because of their popularity as an effective treatment for childhood ADHD. The number of stimulant products available for practitioners has tripled in the last decade. Although stimulants' action on central dopamine systems can be reinforcing, especially when delivered via intraperitoneal or intravenous routes in laboratory animals, they are far less addicting when taken orally by children in the context of a medical treatment. Fortunately, the therapeutic stimulants, available orally, have different pharmacodynamic and pharmacokinetic properties than the illicit stimulants, methamphetamine and cocaine. The lack of intravenous forms of the therapeutic stimulants acts as a natural barrier and tends to prevent addiction. Furthermore, MPH produces dysphoria in school age children, further limiting its reinforcing properties. These pharmacokinetics and pharmacodynamics of methylphenidate and amphetamine treatments for ADHD thus are less addicting because of their delivery systems. Future products, employing novel methods that only allow the drug molecule to be available if ingested, should further increase the safety of these important therapeutic agents.

Review and comparison of the long acting methylphenidate preparations

The stimulants have been the mainstay of pharmacologic treatment for over fifty years. Methylphenidate is the most frequently prescribed of the stimulant agents. In the past, one of the main drawbacks of these agents was the abbreviated duration of action. Over the last few years three longer acting methylphenidate preparations have been released to the market. Though all these agents contain the same chemical compound they do vary in a number of ways. In this article we will present how the formulations compare in their technology and the differences in their delivery systems. We will also compare the available literature that focus on head to head comparisons in terms of pharmacokinetics studies and those reports that present efficacy data. Finally, we will suggest based on a theoretical framework on how to approach selecting an agent based on the results of these trials and the individual needs of the patient.

Comparative efficacy of once-a-day extended-release methylphenidate, two-times-daily immediate-release methylphenidate, and placebo in a laboratory school setting

BACKGROUND

Given the dosing limitations of methylphenidate short-acting preparations in treating ADHD, galenics with longer release of the substance were developed mainly to avoid drug intake during school hours.

OBJECTIVES

This investigation was conducted to assess the efficacy and the duration of action of a new extended-release formulation of methylphenidate (Medikinet retard) as a once-daily treatment for children with attention-deficit hyperactivity disorder (ADHD).

METHOD

This was a randomized, double-blind, crossover multicentre study with three treatment conditions: once-daily extended-release methylphenidate, twice-daily immediate-release methylphenidate and placebo given to 79 children (8-14 years old) with ADHD. Daily assessments in an analogue classroom setting included blind ratings of attention and deportment and a performance measure (math test) obtained 5 times over an 8-hour period. Secondary measures included an ADHD rating scale, based on DSMIV/ ICD-10 separately rated for the morning and the afternoon.

RESULTS

Both active treatment conditions displayed significant time course effects and were superior to placebo in improving all efficacy measures. Once a day extended-release methylphenidate was not different from the same dose of twice daily immediate-release methylphenidate.

CONCLUSIONS

These data provide support for the benefit of this novel, once-daily methylphenidate preparation in the treatment of ADHD. The longer duration of action of Medikinet Retard has the potential to simplify psychostimulant treatment, thus reducing dose diversion and eliminating the need for in-school administration.

New formulations of stimulants for attention-deficit hyperactivity disorder: therapeutic potential

New formulations of stimulant medications for the treatment of attention-deficit hyperactivity disorder (ADHD) have been an important focus for pharmaceutical industry research and development over the past decade. In this article, we review and assess the therapeutic potential of five new stimulant formulations (one immediate release and four longer-acting preparations) that have recently become available for the treatment of ADHD. While the therapeutic potential of immediate-release enantiomers of methylphenidate has not yet been clinically realised, new long-acting formulations of stimulants have changed the standard of care for children, adolescents and adults with ADHD. The longer duration of action of these once-daily compounds, and the consequent expansion of the duration of daily ADHD coverage afforded by them, has introduced the realistic possibility of reducing the overall daily burden of ADHD on affected individuals. Although more expensive, these new stimulant formulations are easier for patients to use than older stimulants, more resistant to abuse and misuse, and allow for increased privacy of ADHD treatment at school or work.

Die Wirksamkeit von Stimulanzien-Retardpräparaten bei Kindern und Jugendlichen mit ADHD - eine systematische Übersicht

Zusammenfassung: Stimulanzien sind das Mittel der Wahl zur pharmakologischen Behandlung einer Aufmerksamkeits-/Hyperaktivitätsstörung. Jedoch ist die Wirkdauer von schnell freisetzenden Präparaten oft nicht ausreichend. Mittlerweile wurden verschiedene retardierte Methylphenidat-, aber auch Amphetaminformen entwickelt, um die Probleme einer mehrfach täglichen Einnahme zu minimieren. Der Artikel stellt die klinischen Studien zu Wirksamkeit, Wirkdauer und Nebenwirkungsprofil verschiedener Stimulanzienformen dar. In der klinischen Anwendung sind die neuen Retard-Produkte wirkungsvolle Alternativen. Eine kontinuierliche mehrstufige Freisetzung des Wirkstoffs über den Tag verteilt nach einmaliger Medikamentengabe bietet Vorteile. Allerdings müssen Nebenwirkungen durch die verlängerte Wirkungsdauer genau beobachtet werden. Eine genauere Anpassung an die jeweiligen Erfordernisse der verschiedenen Tagesabschnitte und -bedürfnisse der Kinder und Jugendlichen ist schwierig. Die Erprobung von Titrierungsschemata unter Einbeziehung von schnell und verzögert freisetzenden Präparaten bleibt eine Aufgabe zukünftiger Forschung.

Effects of Methylphenidate on Attention Deficits After Traumatic Brain Injury

OBJECTIVE

To evaluate the effects of methylphenidate on a variety of aspects of attention, ranging from laboratory-based impairment measures to caregiver ratings and work productivity, in individuals after traumatic brain injury.

DESIGN

A total of 34 adults with moderate to severe traumatic brain injury and attention complaints in the postacute phase of recovery were enrolled in a 6-wk, double-blind, placebo-controlled, repeated crossover study of methylphenidate, administered in a dose of 0.3 mg/kg/dose, twice a day. A wide range of attentional measures was gathered weekly, including computerized and paper-and-pencil tests of attention, videotaped records of individual work in a distracting environment, real-time observational scoring of attentiveness in a classroom environment, and caregiver and clinician rating scales of attentiveness. Participants also attempted to guess their drug condition each week. Data from the first ten participants were used for pilot purposes, to develop attentional factors for composite scoring, and to identify attentional dimensions suggestive of a treatment effect for independent replication. The remaining 24 participants' results were used to confirm potential treatment effects seen in the pilot sample, using Wilcoxon's signed-ranks test on composite factor scores and individual variables.

RESULTS

A total of 54 dependent variables were reduced to 13 composite factors and 13 remaining individual variables. Of the 13 attentional factors, five showed suggestive treatment effects in the pilot sample. Of these, three showed statistically significant treatment effects in the replication sample: speed of information processing (effect sizes, -0.06 to 0.48; P < 0.001), attentiveness during individual work tasks (effect sizes, 0.15-0.62; P = 0.01), and caregiver ratings of attention (effect sizes, 0.44-0.50; P = 0.01). Of the individual variables, four showed suggestive treatment effects in the pilot sample, but only one showed significant treatment effects in the replication sample: reaction time before errors in the Sustained Attention to Response Task (effect size, 0.20; P = 0.03). No treatment-related improvement was seen in divided attention, sustained attention, or susceptibility to distraction. None of the variables showed suggestive or definite negative treatment effects. Effect sizes for those performance measures positively affected by methylphenidate were in the small to medium range and included both impairment and activity level measures. Improvements in processing speed did not seem to come at the expense of accuracy.

CONCLUSIONS

Methylphenidate, at 0.3 mg/kg/dose, given twice a day to individuals with attentional complaints after traumatic brain injury, seems to have clinically significant positive effects on speed of processing, caregiver ratings of attention, and some aspects of on-task behavior in naturalistic tasks. Further research is needed to identify the optimal dose and to extend these findings to less carefully selected individuals.

Pharmacokinetic considerations in the treatment of attention-deficit hyperactivity disorder with methylphenidate

Methylphenidate is commonly used for the treatment of attention-deficit hyperactivity disorder (ADHD). Its efficacy in improving the core symptoms of ADHD, as well as some of the aggressive and oppositional behaviours, is well documented, based on a large volume of research. Methylphenidate has a wide margin of safety and relatively mild adverse effects, most commonly appetite suppression and insomnia. Methylphenidate is a rapidly absorbed medication that, in its d-isomer form, readily penetrates the CNS, particularly the striatum. It appears to function by blocking the reuptake of dopamine. Both the plasma concentrations and behavioural effects of methylphenidate demonstrate a time to maximum of between 1 and 3 hours, with the maximum behavioural effects occurring when the plasma concentrations are increasing. Because of the rapid onset of action, the effects of methylphenidate can be dramatic but usually last only about 4 hours with the immediate-release formulation. The behavioural responses of individuals are also highly variable, so that it is necessary to start treatment at a low dosage and increase up to a maximally effective dosage (usually starting at 10-15 mg/day with increases of 10-15mg at weekly intervals to a maximum dosage of 60 mg/day, irrespective of formulation). Because of the variability in behavioural responses, assessment of plasma concentrations is not clinically useful nor does weight help in deciding an appropriate dosage. The difficulties in administering methylphenidate multiple times a day, particularly during the school day, have been alleviated in the past few years by the development of extended-release preparations with varying behavioural effects lasting 8-12 hours. The 8-hour preparations (Metadate) CD and Ritalin) LA) utilise a microbead technology, while the 12-hour preparation (Concerta) utilises an osmotic pump system. All extended-release formulations effectively control the symptoms of ADHD. While pharmacokinetic differences appear to exist between some of these new formulations, there are currently no clinical data available to demonstrate clinical efficacy differences between them.

Serum and brain concentrations of methylphenidate: implications for use and abuse

When used to treat children with Attention Deficit Hyperactivity Disorder, methylphenidate (MPH) acts primarily by blocking the dopamine (DA) transporter (DAT) and increasing extracellular DA in the striatum. This is strikingly similar to the mechanism of action of cocaine, a primary stimulant drug of abuse. When administered intravenously, MPH like cocaine has reinforcing effects (euphoria) at doses that exceed a DAT blockade threshold of 60%. When administered orally at clinical doses, the pharmacological effects of MPH also exceed this threshold, but reinforcing effects rarely occur. Here we discuss the pharmacokinetic properties of MPH in serum (and in brain) that differ for oral and intravenous routes of administration and the importance of acute tolerance in determining pharmacodynamic effects in clinical use and illegal abuse. We suggest that intravenous administration of MPH mimics the rapid phasic cell firing of DA neurons, which may be a critical factor associated with reinforcing effects and abuse, while oral administration of MPH mimics the tonic DA cell firing, which may be a critical factor associated with clinical effects.

Advances in the Pharmacotherapy of Attention-Deficit–Hyperactivity Disorder: Focus on Methylphenidate Formulations

The psychostimulant dl-methylphenidate (MPH) remains the most common drug therapy in child and adolescent psychiatry for the treatment of attention-deficit-hyperactivity disorder (ADHD). Evidence of a dopaminergic basis both for the actions of MPH and for the underlying neuropathology in ADHD continues to mount. Advances in the biopharmaceutics of MPH have been conspicuous. Novel approaches to formulation design have resulted in new MPH delivery options to overcome the short-term actions of both immediate-and sustained-release MPH. New modified-release MPH products offer the convenience of once-daily administration while providing extended absorption profiles that better mimic those of standard schedules of immediate-release MPH (i.e., the absorption phase of MPH better correlates with improved behavioral response than does the elimination phase). The oral bioavailability of MPH in females may be lower than in males. The l-MPH isomer exhibits only negligible oral bioavailability and, further, possesses little intrinsic activity at the dopamine transporter. This notwithstanding, a single-isomer d-MPH immediate-release product is now available for dosing recommended at one-half that of dl-MPH.

Psychostimulant use in the rehabilitation of individuals with traumatic brain injury

BACKGROUND

Psychostimulants are used commonly in the rehabilitation of individuals with traumatic brain injury (TBI), despite the dearth of well-controlled studies of their effects. The available literature suggests that these drugs predominantly affect the speed of cognitive processing and certain observational ratings of mood and behavior. Effects on sustained attention, distractibility, and memory are less clear.

OBJECTIVE

This article reviews the controlled research literature on the use of these drugs in TBI and presents preliminary data from the authors' laboratory that extends these findings. Some of the common research pitfalls that have limited progress in research on these drugs are discussed.

Methylphenidate bioavailability in adults when an extended-release multiparticulate formulation is administered sprinkled on food or as an intact capsule

OBJECTIVE

To determine the single-dose bioavailability of 20-mg Metadate CD (methylphenidate HCI, USP) Extended-Release Capsules sprinkled onto 1 level tablespoon (15 mL) of applesauce relative to an intact capsule under fasted conditions in healthy adults.

METHOD

This was a single-center, open-label, single-dose, randomized, two-way crossover study with a 6-day washout period between doses, in healthy male and female subjects (N= 26), aged 21-40 years. Plasma concentration-time data for methylphenidate were used to calculate the pharmacokinetic parameters for each treatment.

RESULTS

The pharmacokinetic profile for Metadate CD exhibited biphasic release characteristics with a sharp initial slope and a second rising portion. For Cmax (maximum observed concentration), AUC(0-infinity) (area under the plasma concentration curve from time 0 to infinity) and AUC(0-infinity) (area under the plasma concentration curve from time 0 to the last measurable time point), the geometric least squares mean ratios and 90% confidence intervals were within the 80% to 125% confidence interval for bioequivalence. Adverse events were similar to those reported for methylphenidate.

CONCLUSIONS

The bioavailability of methylphenidate was not altered when Metadate CD capsules were administered by sprinkling their contents onto a small amount of applesauce.

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.

Practice parameter for the use of stimulant medications in the treatment of children, adolescents, and adults

This practice parameter describes treatment with stimulant medication. It uses an evidence-based medicine approach derived from a detailed literature review and expert consultation. Stimulant medications in clinical use include methylphenidate, dextroamphetamine, mixed-salts amphetamine, and pemoline. It carries FDA indications for treatment of attention-deficit/hyperactivity disorder and narcolepsy.

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.

Once-a-day Concerta methylphenidate versus three-times-daily methylphenidate in laboratory and natural settings

OBJECTIVE

Methylphenidate (MPH), the most commonly prescribed drug for attention-deficit/hyperactivity disorder (ADHD), has a short half-life, which necessitates multiple daily doses. The need for multiple doses produces problems with medication administration during school and after-school hours, and therefore with compliance. Previous long-acting stimulants and preparations have shown effects equivalent to twice-daily dosing of MPH. This study tests the efficacy and duration of action, in natural and laboratory settings, of an extended-release MPH preparation designed to last 12 hours and therefore be equivalent to 3-times-daily dosing.

METHODS

Sixty-eight children with ADHD, 6 to 12 years old, participated in a within-subject, double-blind comparison of placebo, immediate-release (IR) MPH 3 times a day (tid), and Concerta, a once-daily MPH formulation. Three dosing levels of medication were used: 5 mg IR MPH tid/18 mg Concerta once a day (qd); 10 mg IR MPH tid/36 mg Concerta qd; and 15 mg IR MPH tid/54 mg Concerta qd. All children were currently medicated with MPH at enrollment, and each child's dose level was based on that child's MPH dosing before the study. The doses of Concerta were selected to be comparable to the daily doses of MPH that each child received. To achieve the ascending rate of MPH delivery determined by initial investigations to provide the necessary continuous coverage, Concerta doses were 20% higher on a daily basis than a comparable tid regimen of IR MPH. Children received each medication condition for 7 days. The investigation was conducted in the context of a background clinical behavioral intervention in both the natural environment and the laboratory setting. Parents received behavioral parent training and teachers were taught to establish a school-home daily report card (DRC). A DRC is a list of individual target behaviors that represent a child's most salient areas of impairment. Teachers set daily goals for each child's impairment targets, and parents provided rewards at home for goal attainment. Each weekday, teachers completed the DRC, and it was used as a dependent measure of individualized medication response. Teachers and parents also completed weekly standardized ratings of behavior and treatment effectiveness. To evaluate the time course of medication effects, children spent 12 hours in a laboratory setting on Saturdays and medication effects were measured using procedures and methods adapted from our summer treatment program. Measures of classroom behavior and academic productivity/accuracy were taken in a laboratory classroom setting during which children completed independent math and reading worksheets. Measures of social behavior were taken in structured, small-group board game settings and unstructured recess settings. Measures included behavior frequency counts, academic problems completed and accuracy, independent observations, teacher and counselor ratings, and individualized behavioral target goals. Reports of adverse events, sleep quality, and appetite were collected.

RESULTS

On virtually all measures in all settings, both drug conditions were significantly different from placebo, and the 2 drugs were not different from each other. In children's regular school settings, both medications improved behavior as measured by teacher ratings and individualized target behaviors (the DRC); these effects were seen into the evening as measured by parent ratings. In the laboratory setting, effects of Concerta were equivalent to tid MPH and lasted at least through 12 hours after dosing. Concerta was significantly superior to tid MPH on 2 parent rating scores, and when asked, more parents preferred Concerta than preferred tid IR MPH or placebo. Side effects on children's sleep and appetite were similar for the 2 preparations. In the lab setting, both medications improved productivity and accuracy on arithmetic seatwork assignments, disruptive and on-task behavior, and classroom rule following. Both medications improved children's rule following and negative behavior in small group board games, as well as in unstructured recess settings. Individual target behaviors also showed significant improvement with medication across domains in the laboratory setting. Children's behavior across settings deteriorated across the laboratory day, and the primary effect of medication was to prevent this deterioration as the day wore on. Results support the use of background behavioral treatment in clinical trials of stimulant medication, and illustrate the utility of a measure of individualized daily target goals (ie, the DRC) as an objective measure of medication response in both the laboratory and natural school settings.

CONCLUSION

This investigation clearly supports the efficacy of the Concerta long-acting formulation of MPH for parents who desire to have medication benefits for their child throughout the day and early evening. (ABSTRACT TRUNCATED)

Assessing the abuse potential of methylphenidate in nonhuman and human subjects: a review

Methylphenidate (MPH) is widely used for the treatment of Attention Deficit Hyperactivity Disorder (ADHD) in children, adolescents, and adults. Methylphenidate is clearly effective for the treatment of ADHD, but there is controversy as to whether it has significant abuse potential like other psychostimulants (e.g., D-amphetamine and cocaine). In general, the drug is believed to be abused at rates much lower than those for other stimulants. The present review examines studies that investigated the behavioral pharmacological profile of methylphenidate and discusses how results from these studies address its abuse liability. Using MEDLINE search terms methylphenidate, drug discrimination, reinforcement, self-administration, subjective effects, subject-rated effects, abuse potential, and abuse liability, along with a review of the references from identified articles, 60 studies were located in which the reinforcing, discriminative-stimulus, or subjective effects of methylphenidate were directly assessed in nonhumans or humans. Forty-eight (80.0%) of the studies reviewed indicate that methylphenidate either functions in a manner similar to D-amphetamine or cocaine (e.g., functions as a reinforcer, substitutes fully in drug discrimination experiments), or produces a pattern of subjective effects suggestive of abuse potential. The results are discussed as they pertain to factors that may account for the apparent discrepancy in abuse rates between methylphenidate and other stimulants, including characterization of actual abuse rates, defining abuse and misuse, pharmacokinetic factors, and validity of abuse liability assays.

How high a dose of stimulant medication in adult attention deficit hyperactivity disorder?

OBJECTIVE

This paper examines clinical and neuroscientific evidence to address the question whether high doses of stimulant drugs offer additional advantages in the treatment of adult attention deficit hyperactivity disorder (ADHD) and at what cost. It attempts to arrive at a reasonable upper limit of dosage for clinical purposes.

METHOD

The study involves a selective review of the treatment studies of ADHD in children and adults and an examination of the pharmacokinetic and pharmacodynamic data on psychostimulants in humans and animals.

RESULTS AND CONCLUSIONS

The clinical and experimental data justify the use of chronic low-dose stimulant treatment of ADHD in adults, with the recommended upper limit of dose being 1 mg/kg for methylphenidate and 0.5 mg/kg for dexamphetamine. There is no empirical evidence of greater improvement with higher doses and any beneficial effect is likely to be compromised by the adverse effects, some of which can be very serious. The recommended doses should be exceeded only after careful consideration and objective documentation of beneficial and adverse consequences. Monitoring of drug levels in blood may be of some value for compliance or pharmacokinetic considerations, as there is a direct relationship between blood and brain levels as well as dopamine transporter occupancy. These recommendations are tentative and further clinical research is warranted.

Methylphenidate: its pharmacology and uses

Methylphenidate is a commonly used medication in the United States. This central nervous system stimulant has a mechanism of action distinct from that of amphetamine. The Food and Drug Administration has approved methylphenidate for the treatment of attention-deficit/hyperactivity disorder and narcolepsy. Treatment with methylphenidate has been advocated in patients with traumatic brain injury and stroke, cancer patients, and those with human immunodeficiency virus infection. Placebo-controlled trials have documented its efficacy as an adjunctive agent in the treatment of depression and pain. This article reviews the current understanding of the mechanism of action and efficacy of methylphenidate in various clinical conditions.

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.

Single- and multiple-dose pharmacokinetics of an oral once-a-day osmotic controlled-release OROS (methylphenidate HCl) formulation

Methylphenidate is used for the treatment of attention deficit hyperactivity disorder (ADHD). OROS (methylphenidate HCl) is an osmotic controlled-release delivery system designed for once-daily oral dosing. The pharmacokinetics of OROS (methylphenidate HCl) 18 mg qd, sustained-release (SR) methylphenidate 20 mg qd, and the immediate-release (IR) formulation given as three 5 mg doses every 4 hours (tid) were compared in adults. In addition, the single- and multiple-dose pharmacokinetics of the OROS formulation were studied. Following OROS (methylphenidate HCl), there was a gradual increase in the mean methylphenidate plasma concentrations with peak concentrations noted at 6 to 8 hours. With the SR formulation, peak plasma concentrations were noted at approximately 4 hours. Following the IR regimen, methylphenidate plasma concentrations fluctuated in tandem with oral dosing; peak concentrations were noted at 6.5 hours. The terminal half-life of methylphenidate was similar for the three formulations. The dose-normalized methylphenidate Cmax for OROS (methylphenidate HCl) was significantly lower than for IR and SR methylphenidate. The bioavailability of methylphenidate and PPA from OROS (methylphenidate HCl) relative to the IR and SR formulations was complete. Mean methylphenidate AUC and terminal half-life were similar after single (32.9 ng.h/mL and 3.9 hours) and multiple doses (35.2 ng.h/mL and 3.9 hours) of OROS (methylphenidate HCl).

Acute tolerance to methylphenidate in the treatment of attention deficit hyperactivity disorder in children

OBJECTIVES

To evaluate the efficacy of several drug delivery patterns of methylphenidate and to determine whether acute tolerance develops to this widely used stimulant medication in the treatment of children with attention deficit hyperactivity disorder.

METHODS

Double-blind trials were conducted in a laboratory school setting in which multiple measures of efficacy were obtained frequently in the morning and afternoon across the school day. In study I, relative efficacy was determined for three dosing patterns of methylphenidate: a standard twice-daily profile, a flat profile, and an ascending profile. In study II, tolerance was assessed by comparison of three-times-a-day regimens in which the time of the middle dose varied.

RESULTS

In study I, the efficacy of the ascending treatment increased across the day, and in the afternoon it was equal to the efficacy of the twice-daily treatment, indicating that an initial bolus was not required for efficacy. The efficacy of the flat treatment declined across the day, and in the afternoon it was significantly less than in the twice-daily treatment, suggesting that tolerance may be developing. In study II, acute improvements in efficacy were reduced to the second of two closely spaced but not to two widely spaced bolus doses, suggesting that shortly after exposure to high concentrations, efficacy is reduced to given concentrations of methylphenidate. In a concentration-effect model, a tolerance term was needed to account for counterclockwise hysteresis.

CONCLUSIONS

Acute tolerance to methylphenidate appears to exist. This should be considered in the design of an optimal dosing regimen for the treatment of children with attention deficit hyperactivity disorder.

Attention-deficit disorder. A paradigm for psychotropic medication intervention in pediatrics

Pediatricians frequently encounter patients with behavioral or academic problems in clinical practice. Assessing and managing these patients requires awareness of the numerous physical, emotional, and psychological causes. Because of their limited contact with these patients during a routine visit, pediatricians as a minimum, should rely on careful parental and social history, teachers' evaluations by checklist, achievement test scores and grades, and the clinicians' own gestalt regarding patients' behavior. This article provides a framework that practitioners can incorporate into their routine office practices. Practitioners must also be knowledgeable about different forms of ADD and learning disabilities, differential diagnosis, and frequently encountered comorbidities. A modest armamentarium of psychotropic drugs potentially useful in the treatment of ADD are available; however, they must be aware of indications, subtle differences in pharmacokinetics, rates of efficacy, and adverse effects for these medications. Appropriate behavioral intervention, educational assessment, and placement when necessary are also essential for optimal management. Enabling the child or adolescent to achieve successfully in school, to experience positive social interactions, and to regain self-esteem are the more rewarding facets of pediatric care.

Comparison of Dissolution between Regular-Release and Halves of Extended-Release Methylphenidate Tablets

Objective:

To compare the in vitro dissolution of methylphenidate hydrochloride from regular-release tablets to halves of extended-release tablets.

Design:

Regular-release 10-mg methylphenidate tablets and halves of 20-mg extended-release tablets from two manufacturers (MD Pharmaceuticals, Inc., and Ciba Pharmaceutical Company) were dissolved according to the USP method specified for regular-release methylphenidate tablets. Samples were collected at 0.25, 0.5, 0.75, 1, 2, 3, 3.5, 4, 5, 6, and 7 hours. Methylphenidate concentration was determined by HPLC.

Results:

Regular-release methylphenidate tablets had statistically greater cumulative dissolution at all sample collection times of 2 hours or less compared with halves of extended-release tablets. The most dramatic difference occurred in the first 30 minutes, at which time the difference in cumulative dissolution was 63% (generic) and 55% (Ritalin). At 3 hours and thereafter, there was no significant difference in cumulative dissolution.

Conclusions:

Despite being cut in half, extended-release methylphenidate still does not dissolve as fast as regular-release tablets. Halving methylphenidate extended-release tablets may be a clinically acceptable means of achieving a prolonged-acting 10-mg dose.

The use of psychotropic medication in preschoolers: indications, safety, and efficacy

OBJECTIVE

To review the indications, safety and efficacy of psychotropic medications used in preschoolers.

METHODS

Proprietary prescription-use databases indicate that practitioners are prescribing psychotropic medications for preschool patients at an increasing rate. A Medline search was conducted using drug exposure for children below the age of 6 years to identify efficacy and safety reports of these agents in the preschool age-group.

RESULTS

The search yielded 22 reports that mention exposure to medications, including maternal exposure, accidental overdose, and adverse events in preschool children. Safety issues highlight the age-specific vulnerabilities of this age-group, including hepatotoxicity from valproic acid, among others. In addition, the prominence of adverse-event responses in this age group may be related to polypharmacy not seen in school-age children or adolescents. Less than a dozen controlled efficacy studies of psychotropic agents were identified for children in the preschool age-group. These are limited by the small numbers of subjects in the reports. Only 2 disorders described in the Diagnostic and Statistical Manual of Mental Disorder (DSM-IV), attention-deficit hyperactivity disorder (ADHD) and autistic disorder, are mentioned. The Food and Drug Administration (FDA) approved psychotropic medications for preschoolers but limited their use to medical purposes, not psychiatric, with the exception of use for ADHD.

CONCLUSION

Because data about psychotropic drug safety and efficacy in adults have not been extended to children, new psychopharmacological research is required before clinicians can use these agents to treat psychiatric disorders in the preschool age-group.

Practice parameters for the assessment and treatment of children, adolescents, and adults with attention-deficit/hyperactivity disorder. American Academy of Child and Adolescent Psychiatry

These practice parameters review the literature on children, adolescents, and adults with attention-deficit/hyperactivity disorder (ADHD). There are three types of ADHD: predominantly inattentive, predominantly hyperactive-impulsive, and combined. Together, they occur in as many as 10% of boys and 5% of girls of elementary school age. Prevalence declines with age, although up to 65% of hyperactive children are still symptomatic as adults. Frequency in adults is estimated to be 2% to 7%. Assessment includes clinical interviews and standardized rating scales from parents and teachers. Testing of intelligence and academic achievement usually are required. Comorbidity is common. The cornerstones of treatment are support and education of parents, appropriate school placement, and pharmacology. The primary medications are psychostimulants, but antidepressants and alpha-adrenergic agonists are used in special circumstances. Other treatments such as behavior modification, school consultation, family therapy, and group therapy address remaining symptoms.

Effect on dissolution from halving methylphenidate extended-release tablets

OBJECTIVE

To determine the effect on in vitro dissolution from cutting methylphenidate extended-release tablets in half.

DESIGN

Ritalin-SR (Ciba Pharmaceutical Co.) and generic methylphenidate extended-release (MD Pharmaceutical Inc.) tablets were dissolved in water according to the method prescribed by the US Pharmacopeia under two conditions: whole and halved. Samples were collected at 15, 30, and 45 minutes and at 1, 2, 3, 3.5, 4, 5, 6, and 7 hours. Methylphenidate content was determined by HPLC.

RESULTS

Halving the tablets caused a statistically significant increase in cumulative dissolution as early as 15 minutes. The difference in cumulative dissolution reached its maximum for both Ritalin-SR and generic methylphenidate extended-release tablets at 2 hours. At this time point, the percent dissolution of the whole versus halved tablets was 57% versus 74% (Ritalin-SR), respectively, and 49% versus 67% (generic), respectively. The dissolution profiles of halved and whole extended-release methylphenidate tablets were parallel from this point through the 7-hour collection period. At 7 hours, however, there was no difference in the cumulative dissolution of halved versus whole tablets.

CONCLUSIONS

While statistical differences during in vitro dissolution do exist and pharmacokinetic ramifications have not yet been determined, the absolute differences in dissolution between halved and whole tablets are not great. Halving methylphenidate extended-release tablets may be a clinically acceptable means of achieving a small increment/decrement in dose without converting to a regular-release tablet.

Attention-deficit hyperactivity disorder. Pharmacotherapy and beyond

Management of ADHD is a challenge that requires time, commitment, and great sensitivity on the part of the physician. Use of stimulant medications is often successful at improving symptoms, but it has become the knee-jerk treatment response for many. Given the wide-ranging effects of ADHD on aspects of patients' lives and the availability of various treatment alternatives, a multimodal approach is considered optimal. As more studies evaluate nonpharmacologic approaches such as behavior therapy, parent education, and neurofeedback and more physicians implement multimodal treatment, outcomes for patients with ADHD are expected to be even more positive.

Medication treatment strategies in the MTA Study: relevance to clinicians and researchers

OBJECTIVE

Clinicians have difficulty applying drug research findings to clinical practice, because research protocols use methods different from those used in daily office practice settings.

METHOD

To design a medication protocol for a multisite clinical trial involving 576 children with attention-deficit hyperactivity disorder (ADHD) while maintaining relevance to clinical practice, investigators from the NIMH Collaborative Multisite Multimodal Treatment Study of Children with Attention-Deficit/Hyperactivity Disorder (MTA study) developed novel medication strategies. These were designed to work either in a monomodal or multimodal format and to ensure standard approaches are used across diverse sites. Each child randomized to medication (projected N = 288) is individually titrated to his or her "best" methylphenidate dose and has individual ADHD symptoms monitored. Decision rules were developed to guide "best dose" selection, dose changes, medication changes, the management of side effects, and integration with psychosocial treatments.

CONCLUSIONS

The MTA study uses a controlled method to standardize the identification of each child's "best" methylphenidate dose in a national, multisite cooperative treatment program. Although the titration protocol is complex, the study's individual dosing approach and algorithms for openly managing ADHD children's medication over time will be of interest to clinicians in office practice.

The use of methylphenidate in the treatment of refractory neurocardiogenic syncope

Recurrent neurocardiogenically mediated episodes of hypotension and bradycardia are a common cause of recurrent syncope that can be identified by head upright tilt table testing. While the use of beta-blockers, theophylline, fludrocortisone, disopyramide, and serotonin re-uptake inhibitors can be helpful in preventing further episodes, some patients are unresponsive to or poorly tolerant of these agents. We investigated the use of the central nervous system stimulant and peripheral vasoconstrictor methylphenidate in preventing both tilt induced and spontaneous neurocardiogenic syncope. Seven patients (all women, mean age 31 +/- 15 years) with recurrent syncope and positive head upright tilt induced hypotension/bradycardia (refractory to normal therapy) were placed on methylphenidate 10 mg orally three times per day. Six of the seven patients became both tilt negative and clinically asymptomatic over a 7-month follow-up period. We conclude that methylphenidate may be an effective therapy in patients with recurrent neurocardiogenic syncope refractory to other forms of therapy.

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.

Enantioselective pharmacokinetics of dl-threo-methylphenidate in humans

A definitive enantioselective pharmacokinetic evaluation of dl-threo-methylphenidate (MPH) was carried out in 11 healthy volunteers, all of whom received, in a randomized crossover design, three oral administrations of MPH: immediate release (IR), slow release (SR), and SR chewed before swallowing (CH). In addition, all subjects received MPH intravenously (IV) on a separate occasion. Both plasma and urine samples were collected for up to 16 hr after each drug administration. Significant enantioselective differences were found in pharmacokinetic parameters such as CL, MRT, Vdss, AUC infinity 0, and t1/2. A profound distortion of the enantiomeric ratio for MPH (d >> 1) was evident in all plasma samples harvested after oral administration. After IV MPH, however, there was no significant distortion in the plasma d/l ratio until 1.5 hr after dosing, whereafter there was a divergence of the plasma levels of the enantiomers. After oral administration of dl-MPH, the absolute bioavailability (F) of d-MPH was 0.23 and that of l-MPH was 0.05. There were no significant differences in renal clearance for d- or l-MPH after oral or IV administration, although the fraction of the dose excreted unchanged in the urine was significantly greater after IV MPH. These data suggest that enantioselective differences in the pharmacokinetics of oral MPH are the result of enantioselectivity in presystemic metabolism rather than in renal excretion, such that l-MPH is preferentially converted into l-ritalinic acid. Finally, it was found that chewing the slow release formulation led to a pharmacokinetic profile very similar to that of MPH-IR, suggesting that MPH-SR should not be prescribed for children who chew tablets.

Attention deficits in school-aged children and adolescents. Current issues and practice

Attention deficits in school-aged children and adolescents pose unique diagnostic and management challenges for the practitioner. While this symptom reflects a heterogeneous spectrum of disorders with varying etiologies, clinical manifestation, treatment needs, and outcomes, there are sufficient common attributes to enable identification and treatment. Accurate diagnosis relies on synthesis of information from history, rating scales, direct observations, and psychometric testing. Close attention must be paid to potential underlying or associated medical, processing, emotional, and psychosocial problems. Multimodal treatment is essential with close collaboration between the child, parents, and professionals. While there is a risk of negative outcomes if the symptoms are left unattended, many of these children also harbor strengths that need to be identified and nurtured.