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Incident User Cohorts for Assessing Medication Cost-Offsets

Keywords: Drug initiator design;statins;cost-offsets.

Objective: To develop and test incident drug user designs for assessing cost savings from statin use in diabetics.

Data Source: Random 5 percent sample of Medicare beneficiaries, 2006–2008.

Study Design: Seven-step incident user design to assess impact of statin initiation on subsequent Medicare spending: (1) unadjusted pre/post initiation test; (2) unadjusted difference-in-difference (DID) with comparison series; (3) adjusted DID; (4) propensity score (PS)-matched DID with static and dynamic baseline covariates; (5) PS-matched DID by drug adherence strata; (6) PS-matched DID for high adherers controlling for healthy adherer bias; and (7) replication for ACE-inhibitor/ARB initiators.

Data Collection/Extraction Methods: Subjects with prevalent diabetes and no statin use (January–June 2006) and statin initiation (July 2006–January 2008) compared to nonusers with a random “potential-initiation” month. Monthly Medicare spending tracked 24 months pre- and post-initiation.

Principal Findings: Statistically significant savings in Medicare spending were observed beginning 7 months post-initiation for statins and 13 months post-initiation for ACEIs/ARBs. However, these savings were only observed for adherent patients in steps 5 and 6.

Conclusions: Drug initiator designs are more robust to confounding than prevalent user designs in assessing cost-offsets from drug use but still require other adjustments and sensitivity analysis to ensure proper inference.

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