A retrospective analysis of the revocation of prior authorization restrictions and the use of antidepressant medications for treating major depressive disorder

Background: The California Medicaid (Medi-Cal) program removed prior authorization restrictions for 2 selective serotonin reuptake inhibitors (SSRIs), fluoxetine and paroxetine, in May 1996. Objective: This article documents how open access affected patient compliance and the likelihood of switching antidepressant therapies. Methods: All Medi-Cal patients with a paid claim who had a diagnosis of major depressive disorder (MDD) from September 1994 through January 1999 were eligible. The impact of open access on patient compliance and drug switching was investigated using logistic regression models. Completed therapy was defined as 180 days of uninterrupted drug therapy at a minimum therapeutic dose. Results: A total of 6409 patient treatment episodes were identified, of which 80% involved the use of an antidepressant. The aggregate rate of drug therapy completion dropped from 23.2% before the change in formulary policy to 20.5% in the open-access period. There was no corresponding change in the likelihood of switching therapies. For fluoxetine-treated patients, the odds ratio for completing therapy relative to tricyclic antidepressant-treated patients dropped from 3.916 to 1.706 in the open-access period. Corresponding results for paroxetine-treated patients were 1.591 and 0.726, respectively. The reduction in the likelihood of completed therapy without a corresponding increase in switching is consistent with earlier results. Open access resulted in an influx of patients who were not previously treated with an antidepressant or reported by their physician as having an MDD. Physicians may have expanded the use of the open-access SSRIs to treat less severely ill patients. However, paid claims data do not provide sufficient information to accurately measure severity of illness. Conclusions: It is unclear whether patients benefited clinically from the expansion of the Medi-Cal formulary. The significant changes in the characteristics of the patient population in response to open access (access effect) complicate attempts to measure the impact of open access on treatment patterns. Future analysis of the impact of open access on the cost of treating an episode of depression will also have to address this issue.