You obviously have never read the Oregon law, nor the many articles that have come out today. It does not legalize euthanasia--it's suicide that's legalized, and the assistance by a physician. The physician will be prosecuted if he administers the medications.
If the physician knows what the drugs are intended to be used for, and of course he or she does in this situation or he/she wouldn't prescribe them, he/she is still morally guilty and in violaion of his/her oath no matter how the law is worded.