Bristol's Plavix revenue, nearly all from U.S. sales, plummeted 60 percent to $741 million in the April-June quarter, even the generics were only available for half that time.
Several analysts said sales would have been a little lower without the coupon strategy.
In another twist aimed at retaining revenue, some drugmakers are offering discount coupons for successor drugs to their blockbusters that have gone off patent. The successor drugs usually bring small improvements and may be approved for slightly different conditions or patient groups. The strategy appears aimed at keeping customers who otherwise would take a generic version of the older drug.
But some companies whose blockbusters are getting many generic rivals at once have chosen not to offer coupons, figuring the rock-bottom prices of those generics would prevent the company from retaining enough patients to make it worth their while.
One example is Merck. Its Singulair asthma and allergy pill, the world's 11th-best-selling drug last year at about $5.5 billion, went off patent on Aug. 3. The company said it expects about 90 percent of sales to evaporate within two months.
Whatever companies decide to do, analysts say it's clear that the coupons are much more effective when there are only one or two generic rivals costing only a little less than the brand-name drug's price.
Analyst Erik Gordon, a professor at the University of Michigan's Ross School of Business, says coupons do help drugmakers retain significant revenue from their blockbusters going off patent, but only in the short run.
"On a big drug, every day that you can delay the sales drop is a happy day at the drug company," Gordon says.
Linda A. Johnson can be followed at http://twitter.com/LindaJ_onPharma
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