title: The use of isotopes in the determination of absolute bioavailability of drugs in humans.
abstract: Absolute bioavailability studies in humans are not routinely performed as part of the drug registration process. They tend to be reasonably demanding, not least because toxicology data are required to support intravenous administration of a drug. Moreover, the classical crossover design of an absolute bioavailability study can suffer from artefacts caused by concentration-dependent pharmacokinetics. Many of the problems associated with absolute bioavailability studies can be alleviated using isotopically labelled drugs. Stable isotopes have been used in the performance of absolute bioavailability studies in humans for > 30 years. More recently, the advantages of using radiolabelled drugs have been expanded by using the ultrasensitive technology of accelerator mass spectrometry. Isotopic labelling not only allows for the accurate and efficient determination of absolute bioavailability, but can also provide information on first-pass effects and other pharmacokinetic parameters.
authors.affiliation: Xceleron Ltd, York BioCentre, Innovation Way, York, YO10 5NY, UK.
authors.forename: Graham
authors.initials: G
authors.lastname: Lappin
authors.forename: Malcolm
authors.initials: M
authors.lastname: Rowland
authors.forename: R Colin
authors.initials: RC
authors.lastname: Garner
mesh_terms: D000283:Administration, Intravesical; D000284:Administration, Oral; D000622:Aminolevulinic Acid / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000493:pharmacokinetics*; D001682:Biological Availability; D002986:Clinical Trials as Topic; D018592:Cross-Over Studies; D006801:Humans; D007275:Injections, Intravenous; D007553:Isotope Labeling; D013058:Mass Spectrometry / Q000379:methods; D008874:Midazolam / Q000008:administration & dosage / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000493:pharmacokinetics*
chemical_list: D019275:Radiopharmaceuticals; D000622:Aminolevulinic Acid; D008874:Midazolam