Plasma and brain stem levels of fenfluramine and norfenfluramine enantiomers were measured in the rat after a toxic dose of racemic fenfluramine (26.1 mg/kg i.p.) and in plasma of volunteers after a single maximal therapeutic dose (60 mg). The ratio between the peak levels reached in the rat and in man was high (35 for racemic fenfluramine). The fraction not bound to plasma protein was about 5 times larger in the rat than in man. The possibility that the supposed toxic effect of fenfluramine may have relevance at the doses given in therapy is discussed.
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