Metabolife 356 Associated With Increased Cardiac Risk

Peggy Peck

November 11, 2003

Nov. 11, 2003 (Orlando) — In a small study of healthy volunteers, a single Metabolife 356 tablet was associated with a 24 millisecond increase in QTc interval on electrocardiogram, an increase that investigators said was associated with a 3.5-fold increase in risk for torsade de pointes, according to results presented here Nov. 9 at the American Heart Association (AHA) Scientific Sessions.

Discussing his results in an AHA press conference, Brian F. McBride, PharmD, from Hartford Hospital, Division of Cardiology and Drug Information, University of Connecticut School of Pharmacy, said the increase in QTc interval was consistent "at one, three, and five hours." Moreover, a single Metabolife tablet — which is just a third of the recommended daily dose — also significantly increased both systolic and diastolic blood pressure.

Metabolife 356 currently "controls about 49% of the world market in diet supplements," McBride said. Metabolife 356 contains ephedra as well as 17 other ingredients and although other studies have suggested an increased cardiac event risk associated with ephedra, McBride said, "we don't really know if ephedra is responsible for these changes; it is possible that another ingredient is responsible." He suggested "safety testing all ingredients to identify true risk."

Metabolife spokesperson Jan Strode told Medscape, "While we haven't reviewed the study yet, all the ephedra studies we have show no link between the herb and serious health effects. We continue to believe that our products are safe and effective when used as directed on the package."

In McBride's study, 15 healthy volunteers, aged 27 ± 3 years, 56% of whom were male, were randomized in a crossover fashion to receive one tablet of Metabolife 356 or matching placebo. Blood pressure, systemic vascular resistance, cardiac output, heart rate, and stroke volume evaluations (BioZ monitor; San Diego, California) were taken at baseline and at one, three, and five hours postdosing. Evaluations were performed at the same time of day to minimize circadian variation and there was a one-week washout period between study phases.

Changes in systolic blood pressure from baseline were 10.00, 7.85, and 15.57 mm Hg higher at one, three, and five hours, respectively, in the Metabolife 356 group compared with the placebo group ( P = .0029, P = .0105, P = .0107, respectively). Changes in diastolic blood pressure from baseline were 5.26, 6.66, and 2.37 mm Hg higher at one, three, and five hours, respectively, in the Metabolife 356 group compared with the placebo group ( P = .0301, P = .0331, P = .1483, respectively). Changes in systemic vascular resistance from baseline were 94.41, 121.27, and 53.49 (dyne*sec)/cm 5 higher at one, three, and five hours, respectively, in the Metabolife 356 group compared with placebo ( P = .0106, P = .00587, P = .0736, respectively).

James J. Ferguson III, MD, FACC, associate director of clinical cardiology research at The Heart Institute in Houston, Texas, told Medscape that "I find these results interesting, but I don't think it means that we would ban Metabolife. I do think it indicates the need to test Metabolife [and] all these nutraceuticals for safety. I think safety testing of all ingredients is necessary." Dr. Ferguson was not involved in the study.

McBride told Medscape that he is not advocating a Metabolife ban, but he does support "doing the same type of safety testing in these products that the [Food and Drug Administration] requires for pharmaceuticals."

In addition, he noted that it is impossible to determine if the results associated with a single dose would "worsen or improve with continued use." But coauthor Jeffrey Kluger, MD, told Medscape that the results seen with a single dose of pharmaceuticals "are not attenuated with time. So the single doseresponse [seen with Metabolife] does, in my opinion, predict long-term outcome."

AHA 2003 Scientific Sessions: Abstract 3540. Presented Nov. 12, 2003.

Reviewed by Gary D. Vogin, MD

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