Once daily (q.d.) osmotic release oral system (OROS) methylphenidate has demonstrated to be as efficacious as three times a day (t.i.d.) immediate release (IR) methylphenidate in children with attention deficit hyperactivity disorder (ADHD) but with superior adherence. However, although ADHD continues into adulthood, data in adults are lacking. Effectiveness, adherence to treatment and patient's satisfaction were studied in adults with ADHD before and after switching from methylphenidate IR to OROS presentation.

Seventy newly diagnosed adults with ADHD were treated with t.i.d. methylphenidate IR and, after 3 months, were switched to q.d. OROS formulation and were followed up during 3 additional months. Effectiveness was evaluated with the ADHD Rating Scale (ADHD-RS) and the Clinical Global Impression Improvement (CGI-I) Scale, adherence to treatment with the Simplified Medication Adherence Questionnaire (SMAQ) and patient satisfaction with the treatment. Effectiveness, adherence and satisfaction were compared before and after treatment switch.

ADHD-RS score changed from 34.6 (10.9) at baseline to 25.1 (9.1) while receiving IR methylphenidate and to 15.1 (7.2) while on OROS formulation. Furthermore, methylphenidate switch was associated with an increase of the rate of patients repondents to treatment, from 28.6% to 91.4%. The administration of methylphenidate OROS was associated with better scores in all items of the SMAQ. Methylphenidate OROS was preferred by 97% of patients. All differences were statistically significant. In conclusion, switch from t.i.d. IR to q.d. OROS methylphenidate was associated with an improvement in adherence, patient's satisfaction, and effectiveness.