ABSTRACT
The study of drugs in vivo is conveniently divided into pharmacokinetics and pharmacodynamics. Pharmacokinetics includes the description of the relationship between dose and concentration while pharmacodynamics describes the relationship between concentration and effect. Bioequivalence is a more complex object, but with only three values — true, false, or undetermined. It can be applied to any pharmacokinetic or pharmacodynamic parameter which characterizes the concentrations or effects arising from a test preparation of a drug. The combination of a pharmacodynamic equivalence based on effects at the site of application and a systemic pharmacokinetic equivalence study would appear to be a realistic alternative to a therapeutic equivalence trial. Symmetrical equivalence intervals for pharmacokinetic parameters would appear to be irrational for drugs with pharmacodynamics that are known to be nonlinear. The pharmacodynamic parameters of sodium excretion have been established for many diuretic agents, especially the loop diuretics.
