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Popular Diet Supplement Increases Both QTc Interval and Blood Pressure: Presented at AHA

By Peggy Peck

ORLANDO, FL -- November 10, 2003 -- In a small study of healthy volunteers, a single Metabolife 356 tablet was associated with a 24 ms increase in QTc interval on electrocardiogram, an increase that investigators said was associated with a 3.5-fold increase in risk for torsades de pointe. The presented their results here on November 9^th at the American Heart Association's Scientific Sessions 2003.

Brian F. McBride, PharmD, fellow in cardiovascular pharmacy, Hartford Hospital, Division of Cardiology and Drug Information, University of Connecticut School of Pharmacy, Hartford, Connecticut, United States, said the increase in QTc interval was consistant "at 1, 3, and 5 hours." Moreover, a single Metabolife tablet -- which is just one-third of the recommended daily dose -- also significantly increased both systolic and diastolic blood pressure.

He noted that Metabolife 356, which contains ephedra and 17 other ingredients, currently "controls about 49% of the world market in diet supplements." Dr. McBride said that although other studies have suggested an increased cardiac event risk associated with ephedra, "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.

Fifteen healthy volunteers (age 27 years; 56% 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, CA) were taken at baseline and 1, 3, and 5 hours post-dosing. 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 mmHg higher at 1, 3, and 5 hours in the Metabolife 356 group compared with placebo (P = .0029, P = .0105, and P = .0107, respectively). The change in diastolic blood pressures from baseline were 5.26, 6.66, and 2.37 mm Hg higher at 1, 3, and 5 hours in the Metabolife 356 group compared with placebo (P = .0301, P = .0331 and P = .1483, respectively). The changes in systemic vascular resistance from baseline were 94.41, 121.27, and 53.49 (dyne*sec)/cm⁵ higher at 1, 3, and 5 hours in the Metabolife 356 group as compared with placebo (P = .0106, P = .00587 and P = .0736, respectively).

Dr. McBride noted that it is impossible to determine if the results associated with a single dose would "worsen or improve with continued use." But co-author Jeffrey Kluger, MD, said in an interview that the results seen with a single dose of pharmaceuticals "are not attenuated with time. So, the single dose response does predict long-term outcome."


[Study title: Does Metabolife 356® Have a Negative Impact on Hemodynamics? Abstract 3540]

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