The pharmacological action of a d r u g corre la tes b e t t e r with t he concentrat ion-t ime course of the d r u g (or i ts active metabolite) in the blood or some o ther biophase t han with the absolute dose adminis tered. This proposit ion is based on empirical evidence demonstrat ing var iabi l i ty

*On sabbatical leave from the Department of Pharmacy, School of Pharmacy, Hebrew Univers i ty , Jerusa lem, I s rae l .