Phentermine: Another diet drug combination comes under fire
New combo also linked to heart valve problems
A new study by researchers at the Massachusetts Institute of Technology and the Massachusetts College of Pharmacy suggests that use of the diet drug phentermine also may lead to the kind of heart valve disorders that caused the popular fen-phen drugs to be taken off the market. Research led to the recall of the drugs fenfluramine (Pondimin) and dexfenfluramine (Redux) earlier this year.
The study notes that after the recall of Redux and Pondimin, many physicians began prescribing phentermine in combination with Prozac as a diet aid. That troubles the study’s authors on two counts. First, researchers say their study found that phentermine interferes with the ability of the monoamine oxidase (MAO) enzyme to deplete excess seratonin. Too much seratonin can, like the workings of fen-phen, make patients less hungry, but at the same time it can lead to the narrowing of blood vessels, which in turn can damage heart valves.
Secondly, the other aspect of a phentermine-Prozac combination, billed as phen-Pro, is that Prozac can interact adversely with MAO inhibitors like phentermine, which Prozac’s labeling already cautions against. But the study’s authors say that has not stopped the combination from being prescribed.
Prozac manufacturer Eli Lilly in Indianapolis already is on record cautioning against the combination, going so far as to ask the diet chain Nutri/System to discourage its use. Lilly adds, however, that no interaction problems have been documented between phentermine and Prozac during the decade Prozac has been available.
The new study’s authors also note that blood vessels narrowed by an overabundance of seratonin also may be linked to primary pulmonary hypertension, a lung disorder that has been associated with diet pills for many years. Phentermine, made by SmithKline Beecham and Medeva Pharmaceuticals, has been available in the United States since 1959.
The authors note that research for the new study was conducted on rats and just 17 human subjects and should be viewed as preliminary. The authors plan to further their research after presenting the preliminary findings at the Interna tional Congress on Obesity.
Just as the MIT study on phentermine was released, three different studies published in The New England Journal of Medicine backed up the heart valve problems that led to the recalls. In the studies, ultrasound techniques were used to examine patients because obvious clinical signs or symptoms did not develop in large patient populations taking the drugs. Still, in one study comparing patients who had taken the recalled drugs vs. those who had not, 23% of the diet pill group had heart valve abnormalities, compared with just 1.3% of the group that had not taken any diet pills.
Another study examined the medical records of 10,000 patients taking the diet drugs and found 11 cases of newly diagnosed problems. In another placebo-controlled study, aortic valve leaks were found in 17% of patients who had taken the drugs, vs. 12% of those who hadn’t. Mitral valve leaks showed up in 61% of the drug takers, vs. 54% of those who hadn’t.
Because there is little disparity between those numbers, the data led researchers to concentrate on the length of time a patient took fen-phen as a factor in subsequent health risks. They doubt patients who took the drugs for less than three months are in much danger. The standard initial regimen for Redux, for example, was 11 weeks at no more than 30 mg a day. They do say, however, patients taking the drug or drugs longer and/or at higher doses should be tested for heart valve problems, although they continue to study whether problems can correct themselves naturally after patients stop taking the drugs.
[For more information on the phentermine study, contact Richard Wurtman at MIT. Telephone: (617) 253-1000. Or call Tim Maher at the Massachusetts College of Pharmacy. Telephone: (617) 495-5797.]
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