pharmacokinetic parameter ratio net flux ratio A pharmacokinetic parameter ratio that describes the drug transmembrane transporter activity regarding an active ingredient or a metabolite in an in vitro bi-directional transport assay using transporter transfected cell model. It is expressed as a ratio of the efflux ratio in cells transfected with the transporter as the numerator and efflux ratio in cells not transfected with the transporter (wild type cells) as the denominator. Mathias Brochhausen Philip E. Empey