CYP2C9*19 is assigned uncertain function due to inadequate evidence. One subject with CYP2C9*1/*19 genotype exhibited decreased clearance compared to wildtype subjects based on tolbutamide plasma concentrations and urine metabolite concentrations after one 500mg dose. This result correlated with the in vitro study where CYP2C9*19 demonstrated 31% enzyme activity with a tolbutamide substrate compared to wildtype (25614704). Multiple in vitro studies similarly found CYP2C9*19 demonstrated decreased clearance with various substrates compared to wildtype (23752738, 23844998, 24118918, 25142737, 25476996, 25144335, 25951663, 25832633, 25884291, 27163851, 24077631), however, one in vitro study showed CYP2C9*19 had similar activity compared to wildtype with a tolbutamide substrate (16099926). Consensus was not achieved among experts and therefore uncertain function was assigned but experts agreed additional evidence may change the assignment to decreased function.