[Pharmacokinetics and metabolism of 3H-synephrine (author's transl)].

The physiological disposition of 1-(4-hydroxyphenyl)-2-methylamino-ethanol-tartrate (synephrine, Sympatol) in man had not been investigated to date. Therefore, we studied pharmacokinetics and metabolism of tritiated synephrine in man. Following short i.v. infusion in six patients about 80% of the administered radioactivity was recovered in urine. Two-thirds of the urinary tritium activity consisted of the deaminated p-hydroxymandelic acid. 10% were excreted as unchanged synephrine only. Following oral ingestion in ten patients the total urinary radioactivity was quite comparable to the i.v. experiments. Therefore, complete enteric absorption has to be stated. The amount of unchanged synephrine amounted, however, only to 2.5% of the dose. The resulting bioavailability has to be calculated to 22% only. The pharmacokinetic parameters are quite comparable to the sympathomimetics similar in structure. The biological half-life was about 2 h. After oral ingestion absorption was fast, the peak concentrations were observed between 1 and 2 h after administration.