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Volume 3 Issue 193 Published - 14:00 UTC 08:00 EST 16-Oct-2001 Next Update - 14:00 UTC 08:00 EST 17-Oct-2001
| Editor: Susan K. Boyer, RN © RAmEx Ars Medica, Inc. All rights reserved. |
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 Generic Antidepressants Threaten Development Of Newer Drug Therapies
The US antidepressant market, valued at $8.5 billion in 2000, grew at a 20% annual rate between 1995 and 2000. However, with the loss of patent exclusivity of selective serotonin reuptake inhibitors (SSRIs), beginning with Eli Lilly's Prozac (fluoxetine) last August, the market for SSRIs and similar drugs is poised for decline for the first time in well over a decade. Novel therapies now under development for the treatment of depression face greater challenges than ever before. The August 2001 arrival of generic fluoxetine will have a profound impact on the depression market in the decade ahead. In addition to eroding the market for branded SSRIs, generic fluoxetine will likely cannibalize sales from other classes of antidepressants. The extent to which prescribers will switch from other branded SSRIs to generic fluoxetine is not yet known. However, a recent internet survey of 72 top-antidepressant-prescribing US primary care physicians revealed that generic switching will impact some branded SSRIs, such as Pfizer's Zoloft, more than others. The survey also showed that physicians were unlikely to prescribe generic fluoxetine if a patient previously had a good response to another SSRI or if the patient requested another SSRI. Growing interest in antidepressants acting at more than one receptor (e.g., serotonin and norepinephrine reuptake inhibitors [SNRIs]) suggests these agents will provide increasingly important alternatives to SSRIs, especially in treatment-refractory patients. This trend will likely be of greatest benefit to American Home Products' SNRI venlafaxine; developmental compounds, such as Eli Lilly's duloxetine, will also enjoy some success. Taking this trend one step further may be triple-acting super neurotransmitter uptake blockers, such as Sepracor's (R)-DDMS. Two other promising new drug classes include NK1 antagonists and corticotropin-releasing factor (CRF) antagonists. Though years away from approval, both classes of drugs could theoretically compete in a variety of depression and anxiety segments with relatively favorable side-effect profiles. However, although NK1 antagonists are further along in development, both of these emerging classes have yet to show evidence of clinical efficacy sufficient to drive significant sales in what is fast becoming a very crowded market. Whether or not any of these new agents will ultimately be successful at fending off encroachment by generics will largely be determined by an ability to successfully treat a broader base of patients (especially those with comorbid anxiety), a "clean" side-effect profile, and a reduced time to onset of action. The drugs currently in clinical development, though promising in some respects, have yet to display all these desired characteristics. |
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