[Biopharmaceutic properties of slow-release codeine phosphate. Drug release from ion exchangers in vitro and in vivo].

The release of bound codeine (CAS 76-57-3) from a cation exchanger was examined in vitro by the flow-through method and in vivo by measuring the plasma concentrations of codeine after administration of slow-release (Codipront Retard) and standard non-retarded drops. Both sets of results show that codeine release from the ion exchanger is protracted and continuous. Relative to the standard formulation the slow-release codeine drops give a lower maximal plasma concentration (Cmax), a delayed time of maximal concentration (tmax), slower absorption (t0.5) and protracted plasma levels. The in vitro and in vivo results were in good agreement.