Intended and Unintended Consequences of the Gabapentin Off-Label Marketing Lawsuit Among Patients With Bipolar Disorder

Objective: The number of lawsuits accusing pharmaceutical companies of off-label marketing has risen in recent years. The impact of such lawsuits on drug prescribing and spending has not been examined. We evaluated a nationwide sample to determine whether the $430 million gabapentin off-label marketing lawsuit and accompanying media coverage affected gabapentin market share, substitution of other scientifically substantiated and unsubstantiated anticonvulsants, and anticonvulsant spending of Medicare/Medicaid patients diagnosed with bipolar disorder.

Method: Using a national 5% sample of Medicare recipients linked to Medicaid claims, we used an interrupted times series design to evaluate the impact of the lawsuit on monthly market share, utilization, and spending from January 1, 2001, to December 31, 2005.

Results: The start of the lawsuit was associated with a 28% relative reduction in gabapentin market share (from ~21% to ~15%) and a reduction in the rate of prescribing from 108 prescriptions per 1,000 patients per month before the start of the lawsuit to 90 by the end of follow-up (P<.001). We also observed increases in market share for 3 other anticonvulsants. Total anticonvulsant use and spending per 1,000 patients increased by 13% and 74%, respectively, after the intervention. The increase in anticonvulsant spending was equivalent to $7,554 per 1,000 patients per year higher than expected compared with the baseline trend (P=.01).

Conclusions: We conclude that the lawsuit resulted in a reduction in gabapentin market share, increased market share for other anticonvulsants, and substantially increased total anticonvulsant spending to approximately half of the settlement amount, not counting substitutions of newer drugs for other illnesses affected by the lawsuit. These findings support the need for further study of the effects of current lawsuits regarding off-label drug marketing.

J Clin Psychiatry

© Copyright 2012 Physicians Postgraduate Press, Inc.

Submitted: March 19, 2012; accepted June 25, 2012.

Online ahead of print: October 16, 2012 (doi:10.4088/JCP.12m07794).

Corresponding author: Meredith J. Chace, MS, Department of Population Medicine, Harvard Medical School and Harvard Pilgrim Health Care, 133 Brookline Ave, 6th Floor, Boston, MA 02215 (mchace@fas.harvard.edu).