Inhibitory effects of the antihistamines epinastine, terfenadine, and ebastine on potassium currents in rat ventricular myocytes.

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.