A new oral erosion controlled drug delivery system with a late burst in the release profile

A new oral erosion controlled drug delivery system on the basis of polyvinyl alcohols with a late burst in the release profile is developed. This late burst occurs after addition of sparingly soluble substances, either excipients like carboxylic acids and neutral cellulose or drugs like theophylline and theobromine. The onset time between 4 and 12 h and the extent of the burst between 20 and 60% are well reproducible and depend on the type of the used additive and the particle size of the basic polymer. For dissociating additives like glutamic acid, the pH within the swelling and eroding hydrocolloid tablet is decisive, differing from the pH of the dissolution medium and controlling the release process. Only polyvinyl alcohols with a ratio of viscosity number to degree of hydrolysis in the range from 2.3 to 3 exhibit acceleration of release in the final phase. As mechanism of the burst, enforced erosion of the gel layer, surrounding the tablet core, could be identified.