Continuity in methylphenidate treatment of adults with attention-deficit/hyperactivity disorder

Although stimulant therapy is commonly discontinued early in adults with attention-deficit/hyperactivity disorder (ADHD), the factors that contribute to continuity of stimulant therapy remain largely unknown.

To (1) compare the continuity of methylphenidate (MPH) therapy among adults who use immediate-release methylphenidate (IR-MPH) for ADHD with adults who use extended-release methylphenidate (ER-MPH) formulations, and (2) examine some of the methodological issues involved in research with administrative claims for ADHD.

An analysis of pharmacy and medical claims for 75 US managed care plans representing approximately 55 million beneficiaries for dates of service from January 1, 2000 through December 31, 2004. Patients had to be adults (aged 18 to 64 years) who had 1 or more outpatient medical claims for ADHD (International Classification of Diseases, Ninth Revision, Clinical Modification code 314.xx) during the study period and who had initiated ER-MPH or IR-MPH treatment for ADHD. The study cohorts did not have a pharmacy claim for MPHs, amphetamines, pemoline, or atomoxetine for 6 months preceding the first (index) MPH pharmacy claim. Stimulant treatment episodes were defined to start on the index date and terminate on the last date supplied of the index medication. Episodes of treatment were also defined as terminated if there was a gap of > or =30 days between the end of the days supplied on the pharmacy claim and the date of the next pharmacy claim for the index medication.

Less than one third (30.0%) of the adult patients who were prescribed MPH had 1 or more medical claims with a diagnosis code for ADHD. For the adult MPH patients with at least 1 medical claim with a diagnosis code for ADHD, the patients who initiated therapy with ER-MPH (N = 2,833) were significantly younger, were more likely to be male, and were less likely to be treated by a psychiatrist than were the patients who initiated therapy with IR-MPH (N = 2,289). Only 50.5% (n = 1,156) of IR-MPH patients and 61.4% (n = 1,739) of ER-MPH patients had more than 1 pharmacy claim for the index MPH medication. Adults treated with ER-MPH also had a significantly longer median duration of treatment with the index medication (ER-MPH: 68 days, 95% confidence interval [CI], 65-71 days vs. IR-MPH 39 days, 95% CI, 33-52 days). Controlling for group differences in age, gender, treatment by a psychiatrist, recently prescribed psychotropic medications, treated mental disorders, emergency mental health treatment, and inpatient mental health care, ER-MPH initiation was associated with an average 27% longer duration of treatment than with IR-MPH (survival time ratio: 1.27, 95% CI, 1.20-1.35).

In management of adult ADHD, use of ER-MPH formulations was associated with a longer median duration of the initially prescribed medication than was use of IR-MPH. It is unknown whether the observed absolute unadjusted difference of 29 days in median length of therapy is clinically important.