Do formulation differences alter abuse liability of methylphenidate? A placebo-controlled, randomized, double-blind, crossover study in recreational drug users.

The primary objective of this study was to determine if the abuse liability of methylphenidate is governed by formulation differences that affect rates of drug delivery. In this double-blind, placebo-controlled, randomized, crossover study, subjects with a history of recreational drug use received single oral doses of placebo, 60 mg of immediate-release methylphenidate (IR) and 108 mg of extended-release methylphenidate (osmotic release oral system [OROS]). Over 24 hours after dosing, blood was collected to determine plasma concentrations of methylphenidate, and subjects completed subjective assessments of abuse liability (Addiction Research Center Inventory, Drug Rating Questionnaire-Subject, and Subjective Drug Value). The abuse-related subjective effects of IR and OROS methylphenidate were statistically significantly different from placebo, confirming the overall validity of the study. Although a higher dose of OROS methylphenidate was used compared with IR methylphenidate (108 mg vs 60 mg), subjective effects were consistently lower for OROS compared with IR methylphenidate (statistically significant for 3 of 6 measures of positive effects), particularly at early time points. In general, pharmacokinetic-pharmacodynamic parameters were correlated from a poor to modest degree, with greater correlations observed for IR methylphenidate. In addition, a post hoc "qualification" method was developed, which demonstrated that pharmacological qualification might improve the assessment of subjective effects. Although requiring epidemiological confirmation, the results suggest that OROS methylphenidate, with its characteristic slow ascending plasma concentration profile, may have lower abuse potential. This conclusion is reflected by lower subjective responses during early hours as compared with the IR formulation with its rapid drug delivery and accompanying greater subjective effects.

Potential interactions of methylphenidate and atomoxetine with dextromethorphan.

OBJECTIVE: To examine the potential for drug-drug interactions to influence drug metabolism between the attention-deficit/hyperactivity disorder (ADHD) dl-methylphenidate and atomoxetine with dextromethorphan, a probe for interactions involving cytochrome P450 (CYP) 2D6 isoenzyme. DESIGN: In vitro and ex vivo analysis of changes in metabolism of study drugs. SETTING: Laboratory. PATIENTS: Not applicable. INTERVENTIONS: Pooled human liver microsomal fractions prepared at CEDRA Corporation (now CellzDirect, Austin, Tex.) by the standard differential centrifugation method (lot 821-1). Human liver microsomes were pooled from 15 donors. Recombinant CYP 2D6-containing microsomes (Supersomes; lots 20 and 24 BD Gentest; Woburn, Mass.) were prepared from a baculovirus-infected insect cell line that expressed only the human CYP 2D6 isoform. Dextromethorphan, with and without effector, was incubated with pooled human liver and recombinant CYP 2D6-containing microsomes. Atomoxetine and dl-methylphenidate were tested at 0.1x, 1x, and 10x their reported therapeutic concentrations. Paroxetine, a known inhibitor of CYP 2D6, was used as a reference agent, and quinidine was used as a positive control inhibitor of CYP 2D6. MAIN OUTCOME MEASURES: Changes in substrate metabolism indicative of CYP 2D6-mediated interactions. RESULTS: Atomoxetine and paroxetine inhibited the formation of dextrorphan by about 50% in human liver microsomes and by more than 80% in recombinant microsomes; the profiles of atomoxetine and the known 2D6 inhibitor paroxetine were similar. High concentrations of dextromethorphan reversed the inhibition of its metabolism, indicating a competitive mechanism of the interaction. Conversely, dextromethorphan and dextrorphan only modestly inhibited atomoxetine and paroxetine metabolism. dl-Methylphenidate did not inhibit dextrorphan formation in either microsome preparation, and dl-methylphenidate metabolism was unaffected by dextromethorphan or dextrorphan. CONCLUSION: These results demonstrate the potential for in vivo interactions between dextromethorphan and atomoxetine in patients with ADHD. However, they do not support the plausibility of an in vivo interaction between dextromethorphan and dl-methylphenidate.

PET study examining pharmacokinetics, detection and likeability, and dopamine transporter receptor occupancy of short- and long-acting oral methylphenidate.

OBJECTIVE: The abuse potential of methylphenidate has been related to the drug's capacity to produce a rapid onset of blockade of the presynaptic dopamine transporter in the brain. An oral once-a-day osmotic controlled-release formulation of methylphenidate produces a more gradual rise in plasma methylphenidate concentration, compared with immediate-release methylphenidate. The authors hypothesized that osmotic-release methylphenidate would also produce a slower onset of blockade of the presynaptic dopamine transporter and would be associated with a lower risk for detection and likeability, compared to immediate-release methylphenidate. METHOD: Twelve healthy adults were randomly assigned to receive single doses of immediate-release methylphenidate or osmotic-release methylphenidate. Doses predicted to produce equivalent maximum concentration (C(max)) values were selected (40 mg of immediate-release methylphenidate and 90 mg of osmotic-release methylphenidate). Plasma d-methylphenidate levels and responses to detection/likeability questionnaire items were obtained hourly for 10 hours after administration of methylphenidate on two separate occasions for each subject. Dopamine transporter receptor occupancies were measured at hours 1, 3, 5, and 7 by using a carbon-11-labeled imaging agent (Altropane) and positron emission tomography. RESULTS: Despite similar C(max) values for both formulations, osmotic-release methylphenidate was associated with a longer time to maximum concentration, longer time to maximum CNS dopamine transporter occupancy, and no detection/likeability, compared with immediate-release methylphenidate. CONCLUSIONS: The findings suggest that the abuse potential of oral methylphenidate is strongly influenced by the rate of delivery and not solely by the magnitude of plasma concentration or brain transporter occupancy. These results advance understanding of the underlying central effects of methylphenidate in humans and identify a potentially less abusable methylphenidate formulation.

Outcomes of OROS methylphenidate compared with atomoxetine in children with ADHD: a multicenter, randomized prospective study.

This community-based study was designed to evaluate treatment outcomes with OROS methylphenidate (MPH) and atomoxetine in children with attentiondeficit/hyperactivity disorder (ADHD), as assessed by physicians and parents in a setting that resembles clinical practice. In a multicenter, prospective, open-label study, children 6 to 12 years of age with ADHD were randomized (2:1, respectively) to 3 weeks of treatment with once-daily OROS MPH or atomoxetine. Investigatorrated measures of symptoms included the ADHD Rating Scale (ADHD-RS) and the Clinical Global Impression-Improvement of Illness scale (CGI-I). Assessments were made at baseline and during a telephone interview in week 1, a clinic visit in week 2, and a final clinic visit in week 3. In total, 1323 patients received OROS MPH (n = 850) or atomoxetine (n = 473). Significant reductions from baseline in investigator-evaluated ADHD-RS scores were observed among patients receiving OROS MPH and those receiving atomoxetine. At the end of the study, mean decreases from baseline ADHD-RS scores were 20.24 for OROS MPH and 16 for atomoxetine (P < .001). Between-treatment differences appeared to increase over time (2.77, 3.44, and 4.24 at weeks 1, 2, and 3, respectively; P < .001). Treatment response (ie, 25% reduction from baseline ADHD-RS scores) was significantly greater at each evaluation for patients taking OROS MPH than for those taking atomoxetine (P < .001). Similar percentages of patients taking OROS MPH (4.8%) and atomoxetine (5.5%) withdrew because of adverse events. Although community-based studies often lack the control of randomized, placebo-controlled trials, these results nevertheless suggest greater ADHD symptom improvement with OROS MPH compared with atomoxetine.

Synthesis and biological evaluation of the major metabolite of atomoxetine: elucidation of a partial kappa-opioid agonist effect.

The major human metabolite of atomoxetine (4-hydroxyatomoxetine) was tested against a panel of receptors and enzymes, and was found to interact with the mu, delta, and kappa-opioid receptors based upon studies involving both binding and functional assays. 4-hydroxyatomoxetine was determined to be a partial agonist of the kappa-opioid receptor.

Efficacy and Tolerability of Famotidine in Preventing Heartburn and Related Symptoms of Upper Gastrointestinal Discomfort.

This randomized, double-blind, placebo-controlled, four-way crossover trial was designed to compare the efficacy of famotidine and placebo in preventing meal-provoked upper gastrointestinal symptoms. One hundred twenty-one subjects (58 men and 63 women), aged 20--61 years, were randomly assigned to one of four treatment sequences which included single oral doses of placebo, famotidine 5 mg, famotidine 10 mg, and famotidine 20 mg, spaced approximately 7 days apart. To be eligible for randomization, subjects had to have at least a 2-month history of heartburn and acid/sour stomach occurring at least three times per week. Treatment was administered 1 h prior to ingestion of test meals (chili and wine). Rescue antacid medication (Maalox((R))) was available for subjects who required additional relief. Heartburn severity. acid/sour stomach, and overall discomfort were evaluated on a six-point scale immediately prior to each test meal and every 15 min thereafter for 5 h. A global evaluation of the test medication, using a five-point scale, was performed prior to rescue medication use or at the end of each treatment session. Heartburn and peak acid/sour stomach were rated as significantly milder following prophylactic treatment with famotidine 5, 10, and 20 mg compared to placebo. Treatment with all three doses of famotidine was rated as "good" or "excellent" by significantly more subjects (58--63%) than following treatment with placebo (38%). In addition, rescue medication was used by significantly fewer subjects following famotidine (17--18%) compared to placebo (37%). Famotidine was generally well tolerated in this trial, with type and frequency of reported adverse experiences similar to that observed following placebo. These results indicated that famotidine doses of 5, 10, and 20 mg were significantly more effective than placebo in preventing symptoms of upper gastrointestinal distress when administered 1 h in advance of meal provocation.