Assessment of bioavailability of experimental single-unit sustained release tablets of verapamil hydrochloride using the stable isotope technique.

A stable isotope technique has been used to assess the bioavailability of sustained release verapamil products. The test formulations were tablets with a core containing 90 mg of verapamil hydrochloride coated with ethylcellulose film, the permeability of which was controlled using different amounts of hydroxypropyl methylcellulose. A product containing ethylcellulose 75% hydroxypropyl methylcellulose 25% w/w gave a single-unit sustained release tablet of verapamil hydrochloride that allowed a dose interval of 24 h. There was no loss in bioavailability, even though verapamil had extensive first-pass metabolism.