Numerical models for calculating the blood level of a drug with oral controlled release forms

Controlled release dosage forms offer advantages over conventional dosage forms and a more constant and prolonged therapeutic effect. These new dosage forms are tested by using in-vitro tests or in-vivo tests; however, a great problem appears with the establishment of correlations between these tests. A new way of working is able to resolve the problem. It consists of coupling either experiments or models based on numerical analysis and computerization. In-vitro tests performed at various pH are used to determine the kinetics of release and the parameters characterizing diffusion or erosion. From the knowledge of the certain data (the gastrointestinal tract-time history, the kinetics of release of the drug out of the dosage form, the rate constants of absorption and elimination, and the plasmatic volume), it is possible to obtain, by calculation, the kinetics of the drug in the plasmatic volume, as well as other pieces of information. Not only is the model able to predict the pharmacokinetics of a drug from a controlled release dosage form, but it also optimizes the characteristics of the dosage form. The validity of the model is successfully tested by comparing the blood level of Theophylline, obtained either by in-vivo tests or calculation.