Two additional kinetic constants are defined and their values given for a number of drugs. These constants can be used when dealing with plasma drug levels reported in Système International Units in order to maintain traditional kinetic calculations in estimating loading doses, infusion rates, and plasma levels from drug ingestions. The constants are termed VDSI and ClSI and are used in place of the traditional apparent volume of distribution and total plasma clearance. Constants for a number of drugs are given.