Fenfluramine

Fenfluramine (3-trifluoromethyl-N-ethylamphetamine, trade names Pondimin, Ponderax and Adifax) is a drug that was part of the Fen-Phen anti-obesity medication (the other drug being phentermine). Fenfluramine was introduced on the U.S. market in 1973. It 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 end result is a feeling of fullness and loss of appetite.

Withdrawal due to heart disease
The drug was withdrawn from the U.S. market in 1997 after reports of heart valve disease, and pulmonary hypertension, including a condition known as cardiac fibrosis. After the US withdrawal of fenfluramine, it was also withdrawn from other markets around the world.

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. In particular norfenfluramine is a potent agonist of 5-HT2B receptors, which are plentiful in human cardiac valves. The suggested mechanism by which fenfluramine causes damage is through over or inappropriate stimulation of these receptors leading to inappropriate valve cell division. Supporting this idea is the fact that this valve abnormality has also occurred in patients using other drugs that act on 5-HT2B receptors.

According to a study of 5743 former users conducted by a plaintiff's expert cardiologist, damage to the heart valve continued long after stopping the medication. Of the users tested, 20 percent of women, and 12 percent of men were affected. For all ex-users, there was a sevenfold increase of chances of needing surgery for faulty heart valves caused by the drug.