Factors affecting zero-order release kinetics of porous gelatin capsules.

Porous gelatin capsules were prepared by entrapping gas bubbles or by drilling in the capsule wall with syringe needles. After hardening by formaldehyde, the capsules were supposed to provide a floating sustained release over 10 hr. Different pore sizes, pore numbers, pore orientational symmetry on the capsule wall, the amount of the effervescent material added to prepare the capsule, the exposure time to formaldehyde, and excipient selected were studied to evaluate their influences on the dissolution kinetics. The gelatin capsules were prepared by adding various amounts of effervescent material or by drilling in the capsule wall with a syringe and then hardening by formaldehyde. Verapamil was used as the model drug and starch or lactose was the only excipient. Verapamil and excipient were mixed and used to fill the prepared capsule. The release of verapamil from the capsules follows the zero-order drug release and was observed after the burst phase. The porous capsule, when filled with the mixture of active ingredients and excipient, can achieve a zero-order release system.