Predictors of concomitant use of antipsychotics and stimulants and its impact on stimulant persistence in pediatric attention deficit hyperactivity disorder.

BACKGROUND Concomitant use of stimulants and atypical antipsychotics is common in pediatric attention deficit hyperactivity disorder (ADHD). However, little is known about the determinants of concomitant use and its utility in the management of pediatric ADHD. OBJECTIVES To (a) examine predictors of concomitant stimulant and atypical antipsychotic use and (b) evaluate the impact of concomitant atypical antipsychotic use on the persistence of stimulants in children and adolescents diagnosed with ADHD. METHODS The retrospective cohort study was conducted using 4 years (January 2004-December 2007) of IMS LifeLink claims data. The study population included children and adolescents aged 6-16 years with a diagnosis of ADHD and those who initiated long-acting stimulants (LAS) from July 2004 to December 2006. Patients were followed for 1 year after index stimulant use. Concomitant use was defined as the concurrent prescription for LAS and atypical antipsychotic agents with at least 14 days overlap after the index LAS claim. Persistence was measured by summing the total number of days a patient remained on the index LAS from the index prescription date with an allowable gap of no more than 30 days. Multiple logistic regression within the conceptual framework of the Andersen Behavioral Model was performed to determine the predictors of concomitant stimulant and atypical antipsychotic use. Multivariate Cox proportional hazards regression within the conceptual framework of the Andersen Behavioral Model was used to examine the impact of concomitant atypical antipsychotic use on persistence of stimulants. RESULTS The study cohort consisted of 39,981 children who initiated LAS treatment. Most (96.10%) received LAS monotherapy, and 3.90% received LAS and atypical antipsychotic concomitantly. The multiple logistic regression analysis found that gender, health insurance, region, year of cohort entry, season, physician specialty, coexisting mental health conditions, and general mental health status influenced the concomitant use of LAS and atypical antipsychotic agents. Bivariate analyses revealed that concomitant users had longer persistence (by 71 days) than the stimulant-alone users. Cox proportional hazards regression revealed that concomitant atypical antipsychotic was associated with improvement in LAS persistence by 15% (HR = 0.85, 95% CI = 0.76-0.94) in comparison with the LAS recipients who did not use atypical antipsychotic concomitantly. Other factors such as age, region, season, coexisting mental health conditions, use of comedications, and general mental health status influenced the LAS treatment persistence among children and adolescents. CONCLUSIONS Various predisposing, enabling, and need factors were associated with the concomitant stimulant and atypical antipsychotic use. Concomitant use of atypical antipsychotics was associated with improved LAS treatment persistence in children and adolescents with ADHD.