A quantitative threshold for high/low extent of urinary excretion of compounds in humans.

In this study, a quantitative threshold was determined for the high/low extent of urinary excretion (UE) of compounds in humans, using a straightforward but robust statistical method known as receiver operating characteristic curve (ROC) analysis, and also 18 potential physicochemical determinants of UE were evaluated. Data on the percent of drug excreted unchanged into the urine, %Ae , were used to determine the threshold for high/low UE. Compounds can be divided into high/low UE groups using the threshold value of Ae  = 16.8%, namely those with Ae  > 16.8% are classified as high UE and those with Ae  ≤ 16.8% as low UE. The %Ae negatively correlated with cLogP (r = -0.56); however, cLogP could not quantitatively predict the value of %Ae (R(2) adj. = 0.32). Several determinants of the extent of UE, including cLogP, ACD labs cLogP and ACD labs cLogD(pH=7.4) , were successfully evaluated as a priori indicators of the extent of UE using two cut-off values for each parameter. Moreover, 87% of the 90 compounds in the external validation set were correctly classified using this approach. Analysis of the physicochemical spaces of compounds in these two groups showed significant overlap, which hinders the a priori determination of the extent of UE of compounds using a single threshold/cut-off value of simple physicochemical parameters. In conclusion, 16.8% is a quantitative threshold value to distinguish between high and low UE and new molecular entities with cLogP and ACD labs cLogP values of ≤0.7 and ≥1.0 and ACD labs cLogD(pH=7.4) values of ≤0.0 and ≥0.5 could be identified as exhibiting high and low UE, respectively.