Impact of 3-tier pharmacy benefit design and increased consumer cost-sharing on drug utilization

To estimate responsiveness of prescription demand within 9 therapeutic classes to increased cost-sharing compared with constant cost-sharing.

Retrospective prescription claims analysis.

Between 1999 and 2001, 3 benefit plans changed from a 2-tier to a 3-tier design (cases); 1 plan kept a 2-tier design (controls). Study subjects needed 24 months of continuous coverage and a prescription filled < OR = 3 months before the benefit change for a nonsteroidal anti-inflammatory agent (NSAID), a cyclooxygenase (COX-2) inhibitor, a selective serotonin reuptake inhibitor (SSRI), a tricyclic antidepressant (TCA), an angiotensin-converting enzyme (ACE) inhibitor, a calcium-channel blocker (CCB), an angiotensin-receptor blocker (ARB), a statin, or a triptan. Changes in use were compared with the Wilcoxon signed rank test. Elasticity of demand among cases was calculated.

Generally, medication possession ratios decreased for cases and increased for controls between 1999 and 2000. Switch rates increased for cases and decreased for controls for all classes but CCBs. Switches to lower copayments for ACE inhibitors, statins, and triptans occurred more often for cases. Discontinuation-rate changes for cases were 2 to 8 times those for controls. Generic-substitution rates depended on availability and initial generic utilization. Elasticity of demand for drugs was generally low, -0.16 to -0.10, for asymptomatic conditions (ACE inhibitors, ARBs, CCBs, statins), and moderate, -0.60 to -0.24, for symptomatic conditions (COX-2 inhibitors, NSAIDs, triptans, SSRIs).

Use of retail prescription medications within 9 specific therapeutic classes decreased as copayment increased. Demand for pharmaceuticals was relatively inelastic with these copayment increases.