Biomedical accelerator mass spectrometry: recent applications in metabolism and pharmacokinetics.

BACKGROUND Accelerator mass spectrometry (AMS) is a sensitive isotope ratio technique used in drug development that allows for small levels of 14C-drug to be administered to humans, thereby removing regulatory hurdles associated with radiotracer studies. AMS uses innovative study designs to obtain pharmacokinetic and metabolism data. OBJECTIVE This review addresses the metabolism and pharmacokinetics relevant to cases where therapeutic drug concentrations are achieved in humans. METHODS The review focuses on two study designs: i) administration of tracer 14C-drug intravenously with a simultaneous non-labelled extravascular therapeutic dose to obtain the pharmacokinetic parameters of clearance, volume of distribution and absolute bioavailability without extensive intravenous toxicology safety studies or formulation development; and ii) use of low levels of 14C-drug during Phase I studies to investigate the quantitative metabolism of the drug in humans early in drug development, as required by the new FDA guideline issued in February 2008. RESULTS/CONCLUSIONS Early knowledge about a drug's clearance, volume of distribution, absolute bioavailability and metabolism can affect the development of a new drug candidate.