A ''Level A'' in vitro/in vivo correlation was established for a susta
ined release theophylline (CAS 58-55-9) preparation (Bronchoretard(R))
under investigation. Such a functional relationship is a valuable too
l for predicting the in vivo performance of a product. Additionally, t
he in vitro specification limits could be justified or even enlarged b
ased on such an extrapolation.