We examined and compared the inhibitory effects of three non-sedating antihistamines, terfenadine, ebastine, and epinastine, on delayed rectifier potassium current (I(K)) and transient outward potassium current (I(to)) of rat isolated ventricular myocytes, using a patch clamp technique. Terfenadine, ebastine and epinastine were found to inhibit I(K) with IC50 values of 5.96, 15.3 and 145 μM, respectively. I(to) was suppressed by epinastine with an IC50 value of 69.5 μM. The order of arrhythmogenicity, assessed by the inhibition of I(K), was ranked as terfenadine > ebastine > epinastine, consistent with that of the potencies of each drug for QT prolongation reported in rats.
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