Analysis of burst release of proxyphylline from poly(vinyl alcohol) hydrogels

The initial high-rate drug release observed at the beginning of many controlled-release processes can be caused by a number of mechanisms, including surface desorption, pore diffusion, or the lack of a diffusion front barrier to regulate the diffusive process. This initial nonsteady-state period is usually referred to as "burst release." A small molecular size drug, proxyphylline, was used as a model solute to study the burst release of a drug from swellable hydrogels based on cross-linked poly(vinyl alcohol) (PVA). The influences of several factors, including drug loading concentration, initial cross-linking ratio of the polymer, initial swollen state of the hydrogel samples, pore diffusion of the drug versus swelling of the hydrogel at the beginning of the release, and osmotic pressure, were investigated to understand the burst behavior. Results show that high drug loading and low cross-linking ratio of the polymer led to more pronounced bursts. Compared, to release experiments starting with relaxed samples, samples in dry states had magnified burst effects, but prolonged the release process. Pore diffusion of the drug at the initial stage and the osmotic pressure were shown not to be effective factors leading to burst release within the range of the experimental conditions of this study.