Pharmacokinetics and allometric scaling of levormeloxifene, a selective oestrogen receptor modulator

The pharmacokinetics of a new selective oestrogen receptor modulator levormeloxifene was investigated in mice, rats, cynomolgus monkeys and humans by compartmental pharmacokinetics. Levormeloxifene was administered as an oral solution in all studies. Allometric scaling was used to predict human pharmacokinetic parameters and the performance of the approach was evaluated. Mean values of clearance confounded by F(CL/F) were 0.073, 0.29, 3.18 and 2.4 l/h in mice, rats, monkeys and humans, respectively. Values of distribution volume at steady state confounded by F(V(ss)/F) were 0.073 and 7.5 l in mice and rats. In monkeys, values of the central volume F(V(c)/F) and volume at steady state F(V(ss)/F) were 28.9 and 57.9 l, respectively. In humans, values of V(c)/F and V(ss)/F were 106 and 587 l, respectively. Predicted CL/F and V(ss)/F showed a linear relationship when plotted vs BW on a log-log scale; for CL/F, r was 0.95-0.98 and for V(ss)/F, r was 0.99. Using allometric scaling the predicted human V(ss)/F deviated 3-fold from the experimentally determined values. Observed values of CL/F deviated 21-25 fold from the predicted, the latter depending on the scaling method. Confidence intervals for the predicted parameters showed major lack of precision for all the allometric scaling methods.