Candidate drug molecules lead compounds

By far the most useful assay is the in vivo assay. Regrettably but understandably, this assay is the most labor-intensive and costly. In vivo assays give the highest quality information about the efficacy of a lead compound. In vivo models are accurate animal models of a human disease. Ideally, a candidate drug molecule should not be advanced in the development process unless it demonstrates good to excellent efficacy in an appropriate in vivo model. 

The desired result of this screening procedure (which may have to be repeated several times with analogs or congeners of the original molecules) is a lead compound, ie, a leading candidate for a successful new drug. A patent application would be filed for a novel compound (a composition of matter patent) that is efficacious, or for a new and nonobvious therapeutic use (a use patent) for a previously known chemical entity. 

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