The Bioavailability of a New Sustained‐Release Preparation of Proxiphylline (Neofyllin Retard®) in the Guinea Pig

Abstract

The bioavailability of a new sustained-release preparation of proxiphylline (neofyllin retard@) has been compared with that of the conventional tablet. The antagonistic action on histamine induced bronchoconstriction in the guinea pig has been used as effect parameter. The results indicate that the release of proxiphylline from the conventional tablet occurred within 85 min. with a maximum antagonistic action of 95 % reached after 70 min., whereas that of the sustained-release preparation was effected more slowly over a period of at least 190 min., resulting in a stable antagonistic action of about 40 % during most of the experimental period. A quantitative analysis of tablets placed in the duodenum for different lengths of time and of the residual amount of proxiphylline in the intestinal content has confirmed that the different shape of the time effect curves obtained with the two tablet formulations is due to a slower release of proxiphylline from the sustained-release tablet than from the conventional tablet. The described in vivo model in the guinea pig has proved useful for the evaluation of the release-and absorption pattern of new sustained-release formulations of anti-asthmatic drugs.