Prodrugs are inactive compounds designed to be converted into pharmaceutically active metabolites following delivery to a patient. Prodrugs have important pharmacokinetic advantages over traditional compounds, and a recent PTAB decision, Lupin Limited v. Vertex Pharmaceuticals Inc. (IPR2016-00558), illustrates how prodrugs can possess patent advantages as well. In its analysis of obviousness, the PTAB focuses on unpredictable results and whether a person of ordinary skill in the art has a reasonable expectation of success in view of the available art, as outlined in Procter & Gamble Co. v. Teva Pharm. USA, Inc., 566 F.3d 989 (Fed. Cir. 2009), frequently applied in pharmaceutical cases.