- FDA warning on codeine use by nursing mothers
- FDA approves updated warfarin (coumadin) prescribing information
Pharmalot has reported on the mixed reactions to the warfarin news. One reaction was that "It's fascinating science, but not ready for prime time." Maybe not in general for all drugs, but the pharmacogenomics of warfarin has been studied for some time, and a greater understanding of the metabolism of this particular drug is critical to its correct application. Warfarin is a very effective drug, but it has two major problems:
1. The difference between the effective dose and a toxic dose is small enough to require close monitoring (i.e. it has a narrow therapeutic window)
2. It is implicated in a large number of adverse effects during ER visits (probably mostly for stroke or blood clots)
The codeine use update is even more urgent. Codeine is activated by the CYP2D6 enzyme, which has a wide variation in our population (gory detail at the Wikipedia link). In other words, the effects of codeine on people vary widely. The morphine that results from codeine metabolism is excreted in breast milk. If a nursing mother is one of the uncommon people who have an overabundance of CYP2D6, a lot of morphine can get excreted into breast milk and find its way into the baby. The results can be devastating. Fortunately, CYP2D6 tests have been approved by the FDA, and the price will probably start falling. Whether this science is ready for prime time or not (and CYP2D6 is probably the most studied of all the metabolism enzymes, so it probably is), it's fairly urgent to start applying this right away.
I applaud the FDA for taking these two steps toward applying pharmacogenomics to important problems. There may be issues down the road, but it's high time we started applying this important science.
