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.