I have been frustrated for years at the roadblocks thrown up by vet's in obtaining prescriptions for heartworm and flea medication. And I've had them refuse to approve a script from a 1-8OO vendor over the phone, even after paying for the required blood test. One vet even implied to me that the same brand name heartworm medication from a mail order vendor might not be "good." I was encouraged by the recent Costco offerings. They mysteriously were able to offer many of the same drugs for 3O% less. It is a profit center for vet offices and they do everything possible to discourage shopping around.