Pharmacology and pharmacokinetics of stereoisomers in radiopharmacy.

Nowadays stereochemistry and biologic stereospecificity are involved in the search for new radiopharmaceuticals. This article reviews: 1) The factors involved in selective distribution of stereoisomers: first-pass effect, binding to plasma proteins, enzyme effect and membrane transport; 2) the distinction between pharmacologic specific receptors and acceptor sites; recognition of stereoisomer ligands by specific receptors of opioids, neuroamines, steroids; 3) the ligands labeled with positron emitter radionuclides useful for tomography: dopaminergic, opiate, serotonergic, benzodiazepine ligands and muscarinic ligands; these ligands are labeled with 11C, 18F or 75Br. The balance between the benefit of using a stereoisomer and the burden of sophistication in its chemical preparation is discussed. In conclusion, there is not a clearcut position in favor of a systematic choice of an enantiomer radiopharmaceutical.