ABSTRACT
This chapter aims to discuss the value of one particular category of pharmacokinetic study in man, using radiolabelled drug, concentrating on practical features of planning and study design. The use of radiolabelled drugs in such studies should be regarded essentially as a preliminary step to the full characterisation of the fate and routes of metabolism of a drug by more specific means, such as gas–liquid or high-performance liquid chromatography procedures. Radioactivity has the advantage of ease of detection; however, it should always be remembered that plasma or urinary levels of activity are non-specific and only follow those fractions of the parent molecule which happen to be labelled. The conventional method of measuring beta-radiation is liquid scintillation counting. For maximum efficiency, the biological sample has to be solubilised in the scintillation fluid. Radioactivity is an emotive subject in which careful assessment of relative risk-benefit ratios is rarely presented with any degree of objectivity.
