The purpose of an ABN is to inform the patient that the "service" may not be covered by Medicare and if the claim is denied, then the patient will have to pay out of pocket themselves.

When your provider agreed to become a Medicare provider, he/she also agreed to be paid what Medicare allows.

As Leah stated, you can accept the loss, you can terminate with Medicare, but you cannot bill the patient for covered services, even though Medicare does not reimburse your costs for the item.

There is nothing stopping you from giving the patient a prescription for the drug and have them buy it themselves. If enough patients lose money on the drug deal, maybe they will see what a hoax Medicare Part D really is.