While it may be true that many medications that are intended for use in people are tested in dogs I don't think that anything close to the majority of testing is done in dogs. Of these nine references, only two deal specifically with disorders likely to be treated by veterinarians in practice and one of these studies only involved nine dogs. The other study involved 42 dogs. Clinical trials are most reliable when a medication is compared against a placebo and neither the patient nor the practitioner know which is being used in any particular patient. Scientific studies may be done for lots of reasons other than clinical use of a medication.
Case reports are the most unreliable of studies.
Out of curiosity, I researched the references listed, since there was a short list of three or four references in all the textbooks. After looking into these references I was able to discern that ALL of the information presented was based on ONE clinical case report in which a dog was treated with a medication and recovered. The dog recovered uneventfully. I am familiar with Tufts University. I hope that this makes my statement a little more clear to you and to other readers of this site.