An oral retard preparation of verapamil (Isoptin retard) is described. The sustained release of the active compound from verapamil retard is obtained by mixing and pressing verapamil hydrochloride with sodium alginate. The proportion of active compound and physiologically indifferent additive may range between 1:1 and 1:2. 2. The determination of the in vitro release according to the half-change method shows that verapamil is completely released from the retard preparation only after 6 to 7 h; with conventional dragées more than 90% of the compound is dissolved already after 10 min. 3. In artificial gastric and intestinal juice (pH 1.4 and 7.5) similar times of release are found. 4. The in vitro results are supported by tests on the intestinal absorption in the anesthetized dog. In a ligated duodenum section verapamil is, 3 to 8 h after application, markedly more slowly released and absorbed from the retard preparation than from conventional dragées.
