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Pharmacokinetics of NS-49, a phenethylamine class alpha 1A-adrenoceptor agonist. 4th communication: tissue distribution, placental transfer and milk secretion of radioactivity in rats after a single oral administration of 14C-NS-49, and effects of repeated administration on its pharmacokinetics.

The tissue distribution, placental transfer and milk secretion of 14C-NS-49 ((R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluoro-methanesulfonanilide hydrochloride, CAS 137431-04-0), a phenethylamine class alpha 1A-adrenoceptor agonist, have been studied after a single oral administration (1 mg/kg) of a suspension formulation to rats. Radioactivity concentrations in tissues were generally highest 1 or 4 h, and for most tissues, exceeded those in the corresponding plasma. Concentrations were generally similar in male and female rats and persisted for at least 24 h. Radioactivity concentrations in most tissues declined in parallel with those in plasma. Placental transfer of radioactivity was low accounting for < 0.1% of the maternal dose. In milk, concentrations were of a similar order to those in the plasma but reached a peak later: the data implied that 14C-NS-49 readily diffused from the plasma into the milk. The absorption, distribution and excretion of 14C-NS-49 have been studied after the repeated administration (1 mg/kg) of a suspension formulation to rats for up to 21 days. At 21 days, radioactivity concentrations in plasma reached a peak 1 h and declined with a terminal half-life of 67 h. Steady state concentrations were reached during 14 days. Peak concentrations in tissues occurred 1 h and, in most tissues exceeded the plasma value. Radioactivity concentrations in tissues appeared to reach steady state during the 21-day dosing period. Tissue and blood cell concentrations declined more slowly than those in the plasma. Radioactivity excretion was relatively constant during the repeated administration and similar in urine (mean 45.8% total dose) and feces (mean 48.2% total dose). At 7 days after the last of 21 daily oral doses, only 0.2% of the total dose remained in the body, indicating that there is no marked accumulation of radioactivity in the tissues. The results obtained in these studies indicated that rats receiving NS-49 at 24 h intervals during chronic and reproductive toxicity studies would be continually exposed to the parent compound and/or its metabolites.