[Control of drug release from coated parenteral matrix-retard tablets using softening agents]

Matrix type tablets containing 7-hydroxyethyltheophylline, L-noradrenaline and L-isoproterenol were coated with Eudragit RS 100 film containing different concentrations of 1,2-propyleneglycol (PG) and tributylcitrate (TBC) as hydrophylic and lipophilic softeners, respectively, to effect a controlled liberation of the substances. In-vitro and in-vivo tests show that PG increasingly accelerates the liberation of active ingredients the longer the tablets are stored, while TBC slows down liberation at a rate that shows no significant change over a storage period of 10 weeks. Depending on the concentration of TBC, the substance will not begin to be released for as long as 36 h, so that in our catecholamine studies on rats, such substances as adrenalin, noradrenalin and isoproterenol may be administered to the experimental animals exogenously after surgical shock has subsided. The experimental data so obtained thus are not distorted in any way.