[Biopharmaceutic investigations with D-norpseudoephedrine (author's transl)].

The concentrations of D-norpseudoephedrine in the plasma of 6 healthy persons were measured after the oral administration of 60 mg D-norpseudoephedrinehydrochloride in a hard gelatin capsule. One-compartment open-model parameters were derived from the blood levels. No gastric absorption was observed. The intestinal absorption started after a lag time of 0.31 h with an absorption constant of 1.75 h-1. The maximum of plasma concentration with 200 ng D-norpseudoephedrine/ml plasma was reached after 1.3 h. The following monoexponential decay of the plasma concentration curve had a half-life of 3 h. 24 h after ingestion no remaining D-norpseudoephedrine could be detected in the plasma. In vitro absorption constants were measured with the Sartorius-Resorptionsmodell. The in vitro results agreed with the in vivo results. The dissociation constant of D-norpseudoephedrine was determined (pKa = 8.92) with a non-logarithmic titration method.