Fenfluramine is a drug that was part of the Fen-Phen anti-obesity medication. Fenfluramine is the racemic mixture of two enantiomers, dextrofenfluramine and levofenfluramine. It increases the level of the neurotransmitter serotonin, a chemical that regulates mood, appetite and other functions. Fenfluramine causes the release of serotonin by disrupting vesicular storage of the neurotransmitter, and reversing serotonin transporter function. The distinctive valvular abnormality seen with fenfluramine is a thickening of the leaflet and chordae tendineae. One mechanism used to explain this phenomenon involves heart valve serotonin receptors, which are thought to help regulate growth. Since fenfluramine and its active metabolite norfenfluramine stimulate serotonin receptors, this may have led to the valvular abnormalities found in patients using fenfluramine.
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