In re Diet Drugs (Phentermine/Fenfluramine/Dexfenfluramine) Products Liability Litigation Lawsuit

In re Diet Drugs (Phentermine/Fenfluramine/Dexfenfluramine) Products Liability Litigation

The product

Fen-phen was the name given to a weight-loss regimen that combined two appetite suppressants, fenfluramine and phentermine. Fenfluramine had been sold in the United States since the 1970s under the brand name Pondimin by American Home Products, the company later known as Wyeth. In 1995, Wyeth also brought to market dexfenfluramine, the active dextro-isomer of fenfluramine, sold under the brand name Redux. Phentermine was a separate, older sympathomimetic stimulant used to suppress appetite. During the early 1990s, physicians increasingly prescribed the two drugs together, and the pairing became one of the most widely used obesity treatments of the decade. Pharmacologically, fenfluramine worked mainly by boosting serotonin activity, while phentermine released primarily norepinephrine.

Regulatory background

The serotonergic mechanism of fenfluramine had caused concern for some time. A chemically related anorectic, aminorex, had already been linked to severe lung damage and was withdrawn from many markets. Within Wyeth, internal discussions in the mid-1990s noted that more cases of pulmonary hypertension had been observed than appeared in the drug's labeling. When dexfenfluramine reached the U.S. market in 1996, the FDA's medical officer had pressed for a boxed warning about pulmonary hypertension; the drug was nonetheless approved without one, while European regulators required prominent warnings.

The alleged harm

In August 1997, researchers at the Mayo Clinic published findings in the New England Journal of Medicine suggesting a link between fen-phen use and mitral valve dysfunction. Following that report, the FDA began receiving hundreds of additional reports of valvular heart disease in people who had taken fen-phen, fenfluramine alone, or dexfenfluramine alone. The damage typically involved the aortic and mitral valves, and the drugs had also been associated with pulmonary hypertension, a rare and often fatal condition.

Echocardiographic studies of patients who had used the combination for up to two years showed abnormal heart valve findings in a large share of them, even among people without symptoms. The rate of abnormal tests was far higher than expected in unexposed individuals, and it rose with duration of use; among those who took the combination for three months or less, the rate of valve complications was low.

In September 1997, the FDA asked the manufacturers to withdraw fenfluramine and dexfenfluramine from the U.S. market, and the products were removed.

The litigation

After the withdrawals, tens of thousands of people who had taken fen-phen or the related compounds filed products liability actions against the manufacturers and others, alleging that the drugs caused valvular heart disease and pulmonary hypertension. The federal courts centralized the cases in multidistrict litigation styled In re Diet Drugs (Phentermine/Fenfluramine/Dexfenfluramine) Products Liability Litigation, MDL 1203, in the United States District Court for the Eastern District of Pennsylvania, where discovery and pretrial proceedings were coordinated.

Resolution

In 2005, the parties reached a global settlement. Under the arrangement, claimants submitted their claims for individual review rather than proceeding to separate trials. The MDL has been terminated as part of that resolution.