Patterns of Atypical Antipsychotic Subtherapeutic Dosing Among Oregon Medicaid Patients

Objective: To examine a cohort of Medicaid patients with new prescriptions for atypical antipsychotic medication to determine the prevalence of subtherapeutic atypical antipsychotic medication use and to identify patient and prescribing provider characteristics associated with occurrence of subtherapeutic use.

Method: This observational cohort study examined Medicaid administrative claims data for patients aged 20 to 64 years with a new prescription for an atypical antipsychotic medication (clozapine, olanzapine, quetiapine, risperidone, ziprasidone) between January 1, 2004, and December 31, 2004. Patient diagnostic information was identified using the International Classification of Diseases, Ninth Revision, Clinical Modification codes on submitted medical claims. Patient characteristics, prescribing provider characteristics, length of therapy, and dosing were examined. A logistic regression assessed the probability of subtherapeutic dosing.

Results: Among 830 individuals in our sample who began treatment with an atypical antipsychotic, only 15% had a documented diagnosis of schizophrenia, subtherapeutic dosing was common (up to 86% of patients taking quetiapine), and 40% continued less than 30 days with the index prescription. A logistic model indicated that a general practitioner as prescribing provider, length of therapy equal to or less than 30 days, and prescription of quetiapine were significantly associated with a subtherapeutic dose (p < .001, p = .028, and p < .001, respectively).

Conclusions: These results suggest that there is extensive use of expensive atypical antipsychotic medications for off-label purposes such as sedation or for other practice patterns that should be explored further. Approaches that minimize off-label atypical antipsychotic use could be of considerable value to Medicaid programs. In addition, these findings support the need for the introduction or increased use of utilization monitoring and the implementation of medication practice guidelines as appropriate decision support for prescribing providers.