Selective serotonin reuptake inhibitor (SSRI) drugs are the most commonly prescribed antidepressants, and any one SSRI is about as good as another SSRI in treating depression, studies have shown. Generic SSRIs are about half the cost of branded ones, however, so you might expect that generic SSRIs would be prescribed at higher rates than SSRIs that are still under patent by the drug companies.
Funny thing, though — a Canadian study found that as soon as the patent expires on an SSRI and the drug goes generic, sales drop significantly, Dr. James M. Bolton and his associates reported at the annual meeting of the American Psychiatric Association.
They analyzed data on all dispensations of SSRIs in Manitoba (population 1.2 million), from 1996 to 2009 and graphed the number of prescriptions filled in pharmacies for each SSRI in the pre- and post-generic periods after adjusting for the effects of age, sex, income, and provincial region.
Among the four SSRIs that were on the market in 1996, sertraline went generic in 1999, fluoxetine’s patent expired in 1994, fluvoxamine went generic in 1996, and a generic form of paroxetine became available in 2003. Citalopram entered the market in 1999 and went generic in 2003.
For every quarter that sertraline was a branded drug, the prescription rate increased 4.6%, and every quarter as a generic drug the prescription rate decreased 1.5%, a statistically significant shift in the usage trend, said Dr. Bolton, of the University of Manitoba, Winnipeg. Paroxetine’s prescription rate increased 4.7% in every quarter as a branded drug and decreased by 1.9% each quarter as a generic, which also was a significant change.
The shift with citalopram was even more dramatic, from a 13.2% increase in prescriptions every quarter it was under patent to a 1.3% increase per quarter after going generic, a 10-fold drop. Pre-generic data were not available for fluoxetine or fluvoxamine, which showed 0.8% and 2.9% decreases per quarter in prescription rates in their post-generic eras.
Essentially, prescriptions favored whichever SSRI was under patent in any particular year, even though much less expensive generic SSRIs were available. General practitioners were more “enthusiastic” about prescribing branded SSRIs than were psychiatrists when both branded and generic forms were available, Dr. Bolton said. Factors other than cost and efficacy seemed to be driving usage, which is concerning given the financial constraints of a public health care system like Canada’s.
Why was this happening? It could be that physicians or patients believed that generics were not as effective as branded SSRIs and didn’t practice evidence-based medicine. Or maybe they were spooked by Health Canada regulatory warnings about possible associations between SSRI use and suicidal behavior, though you’d think that fear would apply to both branded and generic SSRIs.
A third explanation may be the influence of drug company promotion for the branded SSRIs that give them the most profit. In the United States in 2005, pharmaceutical companies spent more than $1 billion to promote SSRIs and serotonin noreprinephrine reuptake inhibitors (SNRIs), including $68 million on physician detailing, Dr. Bolton said. Of the $16.8 billion spent on antidepressant prescriptions in the United States in 2009, $14.2 billion was for branded drugs, he added.
The findings of this Canadian study, however, don’t necessarily apply to the United States, he said. Many U.S. managed care organizations mandate use of less expensive SSRIs instead of more-expensive options. In Canada’s universal health care system, care is free but patients pay out of pocket for medications, so many people buy insurance plans to manage their medication costs. Drug prices do matter to patients on both sides of the border.
Physician detailing isn’t the only way to influence prescribing practices, and news accounts are becoming more common about efforts to separate physicians from drug company influence. Stanford University School of Medicine recently censored five faculty members for violating its conflict-of-interest policy against taking drug company money in exchange for promotional speeches, ProPublica reported.
With control of health care costs near the tops of both U.S. and Canadian politics, I think we’ll be hearing more reports like these.
— Sherry Boschert