Gel ointment of verapamil for percutaneous absorption

A gel ointment of verapamil designed for systemic action by transdermal absorption was prepared. The amount of drug released in vitro decreased progressively when increasing amounts (from 20 to 50%) of ethanol-propylene glycol (2:1, v/v) were incorporated into the ointment. Transdermal absorption of the drug in vivo was studied in rats. Verapamil was found in the systemic circulation, and plasma drug levels were maintained at a plateau for 12 hours after application. The effect of two additives on absorption was also examined. Azone, a cycloheptanone derivative, increased plasma levels of verapamil up to tenfold, the effect being greatly dependent on the amount of alcohols in the formulation. Isopropyl myristate did not influence systemic absorption, but it effectively increased absorption into skin. We conclude that the gel ointment can be used for transdermal drug delivery when an adequate absorption promoter is added.