Importance of analytical methods in pharmacokinetic and drug metabolism studies.

Pharmacokinetic and drug metabolism studies first request that good analytical data are available. The various methods that permit unchanged drugs and their metabolites to be separated, identified and quantitatively assayed are briefly reviewed. The present importance of gas chromatography/mass spectrometry is emphasized, as well as the limits of immunological assays. The sensitivity of the analytical assay has a direct impact on the validity of the pharmacokinetic model which is built up from plasma concentration data. The precision and accuracy of the assay is also critical, and it is not always easily estimated. A new significant parameter is the speed of analysis, and the resulting massive production of analytical data. New drugs coming from biotechnology, and new dosage forms, like targeted drugs, will create new analytical problems in the future. They will probably call for the development of new biological or pharmacological assay procedures, in addition to the physicochemical means of analysis.