Formulation of controlled-release products.

A substantial number of prolonged-release theophylline products are commercially available, each claiming some benefit over a competing product. This paper provides a brief overview of the controlled drug delivery area, starting with the theoretical base of such products, typical biologic constraints related to the oral route of administration, and finally an overview of the type and characteristics of the various sustained- or controlled-release products presently available. It is important to recognize that the preparation of most sustained-release products is on an empirical basis and that it is common to test such products in healthy volunteers under a protocol that bears very little relationship to expected performance in the clinic. Controlled drug delivery, a field that is at least 40 years old in terms of successful commercial products, is just beginning to emerge as a discipline with a strong theory and clinical base.