Effect of Switching Drug Formulations from Immediate-Release to Extended-Release OROS Methylphenidate

Background: The potential advantages of osmotic-release oral system (OROS) methylphenidate (Concerta®) over immediate-release (IR) methylphenidate (Rubifen®) in adults with attention-deficit hyperactivity disorder (ADHD), with respect to medication adherence, effectiveness and tolerability, are yet to be determined. Objective: To compare the adherence, effectiveness and tolerability of OROS methylphenidate versus IR methylphenidate in adults with ADHD. It was hypothesized (after data collection) that adherence and effectiveness would be higher with OROS methylphenidate than with the IR formulation. Study design: A chart review was carried out from April 2004 until April 2005. Setting: Adult ADHD outpatient program in a general hospital in Spain. Patients: Seventy adults with ADHD who met DSM-IV-TR criteria and who did not have any other current major psychiatric disorder. Intervention: Patients were treated with IR methylphenidate three times daily for 3 months and then switched to OROS methylphenidate once daily. Main outcome measure: Effectiveness was assessed by means of the ADHD rating scale-IV (ADHD-RS-IV) and the Clinical Global Impression-Improvement (CGI-I) scale at 3 months (coinciding with treatment switch) and at 6 months. The Simplified Medication Adherence Questionnaire (SMAQ) was used to assess treatment adherence, and was administered at both 3 and 6 months. Results: Seventy adult ADHD patients (mean age ± SD: 30 ± 9.6 years; n = 48 men [68.6%]) were included in this study. The mean baseline ADHD-RS-IV score was 34.6 (SD = 10.9). The mean daily dose of IR methylphenidate was 52.1 mg (SD = 13.8 mg) administered as three divided doses. After the treatment switch, the mean OROS methylphenidate daily dose was 57.9 mg (SD = 16.5 mg) administered once daily. The switch from IR methylphenidate to OROS methylphenidate was associated with a statistically significant improvement in all items of the SMAQ questionnaire. OROS methylphenidate was more effective than IR methylphenidate (p = 0.0005) in reducing symptoms of ADHD. The percentage of responders was 28.6% with IR methylphenidate and 91.4% with the OROS formulation (p = 0.0005). OROS methylphenidate was preferred by 97% of patients. The most common adverse events for each formulation were dry mouth (30% IR methylphenidate) and mood instability (31% OROS methylphenidate). No patients stopped treatment with methylphenidate because of adverse events. Conclusions: The switch from IR to OROS methylphenidate was associated with an improvement in both adherence and effectiveness. There were no differences between IR and OROS methylphenidate in terms of tolerability.