title: Plasma levels and negative chronotropic effect of metoprolol following single doses of a conventional and sustained-release formulation.
abstract: Plasma levels and associated reduction in exercise-induced tachycardia have been examined following the administration of single doses of metoprolol in conventional and slow-release tablets at different times to six healthy male subjects. The study was carried out in two parts. Initially, the tablets were given at 9 a.m. and the subjects were studied up to 14 h and then at 24 h. Subsequently, the same doses were given at 9 p.m. and the subjects were studied 12-24 h after drug administration (i.e. 9 a.m.-9 p.m. the next day). After giving the slow-release tablets the peak plasma levels were significantly lower but the drug persisted in the plasma at higher levels than after the conventional tablet. However, the beta-blocking effect was comparable from the two dosages. The results obtained for the period 12-24 h after the evening dose differed from the corresponding values after morning administration in that the plasma levels were higher and the beta-blocking effects more marked. Furthermore, the half-life values calculated from these data were significantly longer.
mesh_terms: D000328:Adult; D003692:Delayed-Action Preparations; D003864:Depression, Chemical; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007700:Kinetics; D008297:Male; D008790:Metoprolol / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D011412:Propanolamines / Q000494:pharmacology*; D013997:Time Factors
chemical_list: D003692:Delayed-Action Preparations; D011412:Propanolamines; D008790:Metoprolol