QT-Interval Prolongation Produced by Probucol

To the Editor.  —Probucol (4,4′-[(1-methylethylidene) bis (thio)] bis [2,6-bis(1,1-dimethylethyl) phenol]) is a recently introduced drug for the lowering of serum cholesterol levels in familial hypercholesterolemia type II.^1,2 Side effects are considered slight, and no ECG abnormalities have been reported in humans receiving probucol.^2,3 This article describes a reversible QT-interval prolongation in a patient receiving probucol.

Report of a Case.  —A 65-year-old essentially well woman was receiving probucol, 500 mg twice a day, in February 1979 because of hypercholesterolemia (313 mg/dL). An ECG in 1976 was normal (QT_c interval, 0.38 s). When examined again in June 1979, she was asymptomatic. At that time, her cholesterol level was 230 mg/dL; an ECG was not taken. She was examined again on Dec 20, 1979, at which time the ECG (Figure) showed a QT_c-interval prolongation (0.48 s). She was asked to stop taking probucol on Jan 3, 1980. A