The purpose of this article is to provide veterinarians with an understanding of what it means to use a conditionally approved drug. This article summarizes information that has been used to satisfy the reasonable expectation of effectiveness (RXE) standard for conditionally approved companion animal oncology drugs and compares that standard to the substantial evidence of effectiveness (SEE) standard. For conditional approval, the drug company must establish a RXE but need not demonstrate SEE. For a full approval (ie, New Animal Drug Application), the drug company must demonstrate SEE. Information to support a RXE for conditional approval of companion animal oncology drugs has included open-label pilot studies, retrospective analysis of medical records, use of a related formulation, and clinical field studies not meeting their primary effectiveness variable. Oncology drugs are highlighted in this article as they have made up many of the conditionally approved drugs to date. Veterinarians should understand that a conditionally approved drug does not have the same assurance of effectiveness as a drug receiving full approval. However, whether conditionally or fully approved, the drug has been demonstrated to be safe for the intended use. This report did not undergo scientific peer review.
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