OBJECTIVES. Patients receiving methylphenidate for the management of attention-deficit/hyperactivity disorder are recommended to receive periodic hematologic monitoring. The objective of this study was to evaluate the long-term effects of methylphenidate treatment on blood biochemistry and hematologic values.

METHODS. This study involved a detailed analysis of changes in hematologic and blood biochemistry values over the course of a 2-year study of once-daily OROS methylphenidate in otherwise healthy children aged 6 to 13 years with attention-deficit/hyperactivity disorder. Routine hematologic and blood biochemistry assessments were performed at baseline, at 6 and 12 months during study treatment, and at the end of the study.

RESULTS. Of the 407 subjects enrolled in the study, 289 completed year 1, and 229 completed 21 of 24 months. No subject was excluded from entry into the study or discontinued from the study because of abnormalities of any of the blood chemistries evaluated. There were no clinically significant changes from baseline in mean values for hematologic or blood biochemistry parameters. For most values, the mean change in value over the course of the study was <5%.

CONCLUSIONS. These longer-term data suggest that chronic therapy with OROS methylphenidate has no clinically significant impact on laboratory values, challenging the necessity of routine hematologic monitoring in otherwise healthy children with attention-deficit/hyperactivity disorder who are treated with methylphenidate.

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