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Online ISSN: 1099-176X    Print ISSN: 1091-4358
The Journal of Mental Health Policy and Economics
Volume 15, Issue 4, 2012. Pages: 171-178
Published Online: 1 December 2012

Copyright © 2012 ICMPE.


 

Assessing the Comparative-Effectiveness of Antidepressants Commonly Prescribed for Depression in the US Medicare Population

Cameron Kaplan1 and Yuting Zhang1*

1Department of Health Policy and Management, Graduate School of Public Health, University of Pittsburgh, PA, USA

* Correspondence to: Dr. Zhang, Department of Health Policy and Management, University of Pittsburgh, 130 DeSoto Street, Crabtree Hall A664, Pittsburgh, PA 15261, USA.
Tel. +1-412-383 5340
Fax +1-412-624 3146
E-mail: ytzhang@pitt.edu

Source of Funding: Supported by grants (to Dr. Zhang) from US National Institute of Mental Health (RC1 MH088510), and US Agency for Healthcare Research and Quality (R01 HS018657. Dr. Zhang recently completed a study to evaluating the effects of high deductible health plan that was partially funded by Highmark Inc., which sells Part D products.

Abstract

This study assessed the comparative-effectiveness of three antidepressants (escitalopram, citalopram, sertraline). We used 2008-2009 pharmacy and medical claims data for a 5 percent random sample of US Medicare beneficiaries diagnosed with depression in 2008. Key measures included drug spending, medication adherence to antidepressants, and down-stream medical costs. Three methods were conducted: generalized linear regression, propensity score matching, and instrumental variables (IV). For the IV approach, we used geographic variation in prescriptions as instruments. The regression and the propensity score methods each showed that patients using escitalopram had significantly worse adherence, higher drug costs, and higher medical costs than patients using either citalopram or sertraline. However, the IV analysis showed that while drug costs remained significantly higher for escitalopram patients, they had lower, offsetting non-drug medical spending than patients who used citalopram. All three models showed that sertraline was at least as cost-effective as or more cost-effective than the other drugs.

 

Background: Depression is among the most common chronic illnesses in the US elderly Medicare population, affecting approximately 11.5% of beneficiaries with estimated costs of about US$65 billion annually.  Patients with depression are typically treated with antidepressants - most commonly the Selective Serotonin Reuptake Inhibitors (SSRIs). SSRIs vary substantially in their costs, side effect profiles and convenience of use. All these factors might affect medication adherence and subsequently down-stream medical costs.

Aims of Study: To assess the comparative-effectiveness of three antidepressants (escitalopram, citalopram, sertraline) commonly-prescribed for depression in Medicare.

Methods: We used pharmacy and medical claims data for a 5 percent national random sample of Medicare beneficiaries who were diagnosed with depression in 2008 and followed until 12/31/2009. Key measures included drug spending, medication adherence to antidepressants, down-stream non-drug medical costs at three levels: all, psychiatric and depression related costs. Three methods were conducted to test robustness: generalized linear regression (GLM), propensity score matching, and an instrumental variables (IV) approach. For the instrumental variables approach, we used a two-stage residual inclusion model, using geographic variation in the use of the various drugs as instruments.  Specifically, we calculated the ratio of the number of individuals who used each drug to the total number of individuals using any antidepressants at the 306 Dartmouth hospital-referral regions.

Results: The regression and the propensity score matching method each showed that patients using escitalopram had significantly worse adherence, higher drug costs, and higher medical costs than patients using either citalopram or sertraline. However, our IV analysis yielded different results. While drug costs remained significantly higher for escitalopram patients, we found that escitalopram users had lower non-drug medical spending than patients who used citalopram, which was enough to offset the higher drug costs.  The instrumental variables results also suggested that sertraline users had lower non-drug medical costs than citalopram users. The differences between sertraline and escitalopram were not statistically significant for medical spending, but sertraline users had lower drug costs and better adherence than escitalopram users.

Discussion: The IV method yielded somewhat different results than the GLM regressions and the propensity score matching methods. Once we controlled for selection bias using the instrumental variables, we found that escitalopram is actually associated with lower medical spending.  One interpretation is that the IV approach mitigates selection biases due to unobserved factors that are not controlled in regular regressions. However, one conclusion remains the same: in every model, we found that sertraline was at least as cost-effective as or more cost-effective than the other drugs.

Limitations: Potential unobserved factors affecting the choice of three antidepressants are possible.

Implications for Health Policies: All methods indicated that sertraline is the most cost-effective drug to treat depression.  Substantial savings to Medicare could be realized by using more cost-effective antidepressants such as sertraline.

Implications for Further Research: Geographic variation in the use of prescription drugs has been underutilized as an instrumental variable in comparative-effectiveness research. Our study demonstrates that it can help to control for selection biases in observational data.


Received 30 January 2012; accepted 27 October 2012

Copyright 2012 ICMPE