In order to designate a product as an orphan drug, the scientific rationale portion of the designation request must include enough information to establish a medically plausible basis for expecting the drug to be effective in the rare disease. This is best supported by clinical trials of the drug in the rare disease or condition. However, in absence of human data, the request for orphan drug designation may be satisfactorily supported with preclinical data that uses the active moiety or principal molecular structure of the proposed orphan drug in a relevant animal model for the rare human disease. Animal toxicology data, which describes the safety of the drug in animals, does not provide efficacy data, so it is not generally relevant in supporting the scientific rationale section of the orphan drug designation.
