WSJ reports controversies over FDA’s suggested gene-based approach to warfarin prescribing
In Milestone, FDA Pushes Genetic Tests Tied to Drug - WSJ.com
Kudos to Anna Wilde Matthews, from the Wall Street Journal (Subscr. Req.), who has done a superb job documenting some of the practical difficulties of implementing genetic predictors of therapeutic response in clinical practice. Here’s a snippet from her piece:
Some specialists say testing hasn’t been proved to reduce the risks of the drug. They fear patients who don’t get the tests and run into trouble will sue doctors, citing the drug’s label. While Medicare covers the tests, which generally cost between $300 and $500, major insurers such as Aetna Inc., WellPoint Inc. and Cigna Corp. don’t. The insurers say they need more evidence about the benefits. “It would be irresponsible and potentially harmful to suggest that testing be used, or even mentioned, in the label,” said University of Washington professor Ann Wittkowsky in an interview before the FDA’s decision. “It is fascinating science, but it is not yet ready for prime time.” Larry Lesko, director of the clinical pharmacology office at the FDA, says the agency has “substantial” evidence to support the new label and hopes it will improve safety by informing doctors.
Dr. Lesko’s hope for a benefit of the genetic predictors is commendable; it shows he’s open to supporting new ways of improving the safety of potentially dangerous drugs. It’s also irrelevant to prescribers and insurers who need evidence of actual benefit, not just the hope of benefit, to guide their practices. Before FDA supports the widespread use of such theranostics, it must require theranostics vendors, or in some cases drug manufacturers, to perform the clinical studies needed to support their use.
In the absence of such studies, doctors prescribing warfarin should not deviate from their current empirical dosing practices using measurement of INR to gauge response. The one exception to this recommendation is a high suspicion of genetic predisposition to atypical warfarin pharmacokinetics based on a suggestive family or personal history. In such cases, the prior probability of a positive test might warrant its use prior to dosing.
Data on genetic predictors:
