Sim Bio Sys gets around this quandary by accelerating drug kinetics to faster than real time. Provided these are all set to the same value, then the steady state reached by any drug will be correct, although the rate of approach to equilibrium will be different. Drug Kinetics Drug kinetics are described with a single compartment model, based on standard estimates of volume of distribution. Protein binding is not explicitly included. Administration of bolus drugs are assumed to distribute instantaneously into this volume of distribution, so that onset of action of bolus drugs is faster than is seen in real life.
Elimination includes a combination of renal and metabolic clearance.
Renal clearance includes both a linear tubular secretion model and a linear GFR dependent model. Tubular reabsorption is not described for drugs. Metabolic clearance is described using a Michaelis Menten model. Many drugs are metabolically eliminated, but their Km's are not known. In cases where data is unavailable, we have chosen Km values that are large compared with active concentrations of the drugs.