Table 2

In vitro PK parameters
Experiment types Parameters Description Unit References
Single Drug Metabolism Experiment Km Michaelis-Menten constant. mg L-1 Segel p28.
Vmax Maximum velocity of the enzyme activity. mg h-1 mg-1 protein Segel p19
CLint Intrinsic metabolic clearance is defined as ratio of maximum metabolism rate, Vmax, and the Michaelis-Menten constant, Km. ml h-1 mg-1 protein RT p165
Metabolic ratio Parent drug/metabolite concentration ratio NA
fmenzyme Fraction of drug systemically available that is converted to a metabolite through a specific enzyme. NA RT xiii
Single Drug Transporter Experiment Papp The apparent permeability of compounds across the monolayer cells. cm/sec Transport Consortium
Re Re is the ratio of basolateral to apical over apical to basolateral. NA Transport Consortium
Radioactivity Total radioactivity in plasma and bile samples is measured in a liquid scintillation counter dpm/mg protein Transport Consortium
Uptake Volume The amount of radioactivity associated with the cells divided by its concentration in the incubation medium. ul/mg protein Transport Consortium
Drug Interaction Experiment IC50 Inhibitor concentration that inhibits to 50% of enzyme activity. mg L-1
Ki Inhibition rate constant for competitive inhibition, noncompetitive inhibition, and uncompetitive inhibition. mg L-1 Segel p103
Kdeg The natural degradation rate constant for the Enzyme. h-1 Rostami-Hodjegan and Tucker
KI The concentration of inhibitor associated with half maximal Inactivation in the mechanism based inhibition. mg L-1 Rostami-Hodjegan and Tucker
Kinact The maximum degradation rate constant in the presence of a high concentration of inhibitor in the mechanism based inhibition. h-1 Rostami-Hodjegan and Tucker
Emax Maximum induction rate Unit free Rostami-Hodjegan and Tucker
EC50 The concentration of inducer that is associated with the half maximal induction. mg L-1 Rostami-Hodjegan and Tucker
Type of Drug Interactions Competitive inhibition, noncompetitive inhibition, uncompetitive inhibition, mechanism based inhibition, and induction. Rostami-Hodjegan and Tucker

Note: Segel H. Irwin. Enzyme Kinetics – Behavior and analysis of rapid equilibrium and steady state enzyme systems. John Wiley & Sons, Inc. 1975, New York. Rostami-Hodjegan Amin and Tucker Geoff ‘In silico’ simulations to assess the ‘in vivo’ consequences of ‘in vitro’ metabolic drug-drug interactions. Drug Discovery Today, 2004, 1, 441–448. The International Transporter Consortium, Membrane transporters in drug development. Nature Review Drug Discovery, 9, 215–236. Rowland Malcolm and Tozer N. Thomas Clinical Pharmacokinetics Concepts and Applications, 3rd edition. 1995, Lippincott Williams & Wilkins.

Wu et al.

Wu et al. BMC Bioinformatics 2013 14:35   doi:10.1186/1471-2105-14-35

Open Data