Selective contracting and patient outcomes: A case study of formulary restrictions for selective serotonin reuptake inhibitor antidepressants

Objectives: Many health maintenance organizations (HMOs) have selected 1 or 2 selective serotonin reuptake inhibitors (SSRIs) as their preferred drug for treating depression. This study investigated the effect of "single-drug " formulary restrictions on the likelihood of drug therapy completion for n ew patients, controlling for initial SSRIs used and other factors. Methods: Prescription drug and medical record data for 187 patients who wer e newly prescribed SSRIs were retrieved from a single California group prac tice consisting of 22 board-certified primary care physicians. The group pr actice contracted with 2 independent practice association-model HMOs with d ifferent SSRI formulary restrictions. A multivariate analysis of drug thera py completion was conducted and 2 sensitivity analyses were performed. Comp leted therapy was based on the patient having achieved 6 months of uninterr upted therapy at a minimum therapeutic dose. Results: Patients from the HMO with a single preferred SSRI (paroxetine) we re 80% less likely to complete therapy than were patients from the HMO with 2 preferred SSRIs (fluoxetine and paroxetine) (odds ratio [OR] = 0.200, 95 % confidence interval [Cl] = 0.083-0.430). This formulary effect was indepe ndent of the initial drug used to treat the patient. Drug selection was als o found to affect completion rates, Patients treated with sertraline were s ignificantly less likely to complete therapy than were patients treated wit h fluoxetine (OR = 0.319, 95% CI = 0.105-0.968). Similar results were found for patients taking paroxetine relative to fluoxetine (OR = 0.357, 95% Cl = 0.149-0.853). Conclusion: These results suggest that the use of single-product formularie s may have unintended consequences on patient completion rates, independent of whether or not the most effective product is selected for preferred for mulary status.