In the conscious dog the duration of action of verapamil, usual galenic preparation (Isoptin, Cordilox), and of verapamil retard (Isoptin retard: verapamil mixed and pressed with the swelling agent sodium alginate) was tested by measuring the blood pressure decrease occurring with higher dosage. Furthermore lead II of the ECG was recorded. 2. Already 2 h after oral application of verapamil retard a significant action is observed. As had been expected verapamil retard shows a slightly protracted onset of action compared to verapamil. 3. At the end of the test period, 12 h after administration, the effect of verapamil retard is still significant. In equipotent dosage its duration of action is clearly superior to that of conventional verapamil dragées. 4. During the period of 2 h to 12 h the intensity of action of verapamil retard shows only slight variations; significant differences could not be detected. 5. Verapamil mixed and pressed with sodium alginate, used as swelling substance and food additive, is an adequate preparation which allows the oral administration of verapamil with very long duration and almost constant intensity of action.
