INHIBITORY EFFECTS OF TERFENADINE ON THE RISING PHASE OF ACTION-POTENTIALS AND SINUS RATES IN ISOLATED GUINEA-PIG MYOCARDIUM

1. Effects of terfenadine on the ventricular action potential and sinu s rate of isolated guinea pig myocardial preparations were examined to elucidate whether the drug has any cardioinhibitory effect. 2. Terfen adine significantly and concentration dependently decreased the maximu m rate of rise (V-max) of action potentials, the decrease of which was 60% of the control value at 2 x 10(-5) M. 3. Terfenadine decreased th e sinus rate concentration dependently at 10(-6) M and higher concentr ations; in some preparations, spontaneous beating was abolished at 2 x 10(-5) M (sinus arrest). 4. On the other hand, KW-4679 -[3-(dimethyla mino)propylidene]-6-11-dihydrodibenz [b,e]oxepin-2-acetic acid hydroch loride), a new antiallergic drug having higher antiallergic potency th an terfenadine, exerted a weaker inhibitory effect on the V-max withou t affecting the sinus rate. 5. In conclusion, the antiallergic drug te rfenadine has inhibitory effects on isolated myocardial The cardioinhi bitory effects of antiallergic drugs seem to be independent of their a ntiallergic potency.