After a gentle linear climb from 1999 to mid-2001, Medicaid's cost per 75-mg unit increased from $3.40 to $3.80 over the following two quarters. It then resumed the former slow, steady increase, reaching about $4 in late 2005.
Prior to the ad campaign, total Medicaid pharmacy costs for Plavix were increasing steadily by $95.68 per quarter per 1,000 enrollees, Law and colleagues said
They found an "elbow" in the curve that coincided with the campaign's start.
"Overall, these estimates indicate a 25 percent increase in reimbursement by the end of 2005 beyond that which would be expected based on the existing [pre-advertising] trend," the researchers wrote.
"Multiplying the increase in rate by the enrolled population in each quarter, this equates to an additional $207 million in pharmacy reimbursement over the study period."
They said the lack of significant change in per-enrollee usage of Plavix after the ads started was unexpected, although, in an earlier study, the same researchers also found no long-term effect of advertising on usage of three other drugs.
Law and colleagues cautioned that their findings do not prove that consumer-oriented ad campaigns increase drug costs.
"Offsetting the costs of direct-to-consumer advertising may have been one of several potential motivations for the increase in per-unit cost of Plavix; other factors that might play a role in price setting include anticipating increased Plavix sales, concurrent changes in the sales of the manufacturers' other drugs, overall market conditions, and research and development costs for future products," they noted.
The researchers also said their findings might have been unique to Plavix and its advertising. They pointed out that responses to advertising could be different for drug classes in which several competing products are advertised, which was not the case with Plavix.
Another limitation was that the study did not examine marketing to physicians, which might also affect prescription rates.
Woloshin and Schwartz, in their editorial, said that one way to stay afloat in the "deep sea" of skewed industry marketing would be to make FDA information on drugs more widely available.
"The FDA should create standardized executive summaries of drug reviews that quantify the benefit and important harms found in the Phase III trials," they wrote, recommending that the summaries be posted on the agency's Web site and attached to all advertising materials.