Abstract: A system for simulating metabolism of a compound in a mammal is disclosed that includes a metabolism simulation model of a mammalian liver. This model has equations which, when executed on a computer, calculate the rate of metabolism of the compound in the cells of the mammalian liver and a rate of transport of the compound into the cells, wherein the simulation model determines an amount of the metabolism product. The rate of metabolism may be a rate of depletion of the compound. The metabolism product may be an amount of the compound remaining after the compound's first passage through the mammalian liver (This is not necessarily limited to first pass, nor would it need to be limited to the liver. Intestinal metabolism could also be modeled). The rate of metabolism may alternatively be a rate of accumulation of a metabolite of the compound.