[Quantitative determination of mefexamide and its main degradation product desmethyl-mefexamide in human urine after ingestion of therapeutic doses (author's transl)].

After oral ingestion of 400 mg Mefexamidehydrochloride for Mefexamide (I) and its main degradation product Desmethyl-Mefexamide (II) the following pharmakokinetic parameters have been determined: 1. Elimination of I and II follows 1st order kinetics. 2. Biological half-life t 1/2 for I is 4-6, for II 4.5-6.5 H. 3. Elimination rate constant for I and II is between 0.10 to 0.20 h-1. 4. 5-10% of the administered drug are excreted unchanged, 10-16% as Desmethyl-Mefexamide within 72 h after ingestion. 5. The described thinlayer chromatographic and gas chromatographic/mass spectrometric methods allow detection of I and II for at least 72 h after application. 6. II is excreted free and conjugated in nearly equal amounts.