Chorin E, et al. - Using the Guidelines for the Clinical Evaluation of QT/QTc for Non-antiarrhythmic Drugs, researchers performed this open-label, randomized, crossover study with blinded outcome evaluation to determine the impacts of grapefruit juice on the QT interval in 30 healthy volunteers and 10 patients with congenital long QT syndrome. They asked healthy volunteers to drink 2 liters of grapefruit juice (in divided doses) or to take 400 mg oral moxifloxacin. They screened and coded repeated baseline, off-drugs and on-drugs (grapefruit or moxifloxacin) electrocardiograms. Findings revealed prolongation of the QT interval with grapefruit juice at the doses tested. This impact was significant in healthy volunteers, similar to that with moxifloxacin; it was even greater in females and more so in patients with long QT syndrome.