Stereoselective disposition of fenfluramine enantiomers in the rat.

1. Rats were treated with d-, l-or dl-fenfluramine. The two optical isomers and their metabolites were determined in plasma, red blood cells and brain areas such as striatum and brainstem. 2. In all cases, the levels of d-fenfluramine were higher than those of the l-enantiomer, while levels of the metabolite norfenfluramine were lower for the d- than the l-form. 3. When metabolism of fenfluramine was inhibited by pre-treatment with SKF 525-A, the concentrations of the enantiomers no longer differed.