Metabolic Fate of a New Analgesics l-1, 4-Dimethyl-10-hydroxy-2, 3, 4, 5, 6, 7-hexahydro-1, 6-methano-1H-4-benzazonine Hydrobromide (l-ST-2121). I. Absorption, Distribution and Excretion of l-ST-2121 in Rats

Abstract

Absorption, distribution, excretion, and placental transfer of ¹⁴C-l-ST-2121 were studied by the tracer technique after its subcutaneous injection in male and female rats. ¹⁴C-l-ST-2121 was rapidly and almost quantitatively absorbed from the subcutaneous region. The radioactivity in blood reached the maximum level within 1 hr, and biphasic time course was observed. The radioactivity was rapidly distributed throughout the tissues. A high concentration of radioactivity was observed in the liver, kidneys, lung, hypophysis, Harderian gland, salivary gland, adrenal, and preputial gland. At 48 hr, a very low concentration was found in the tissues. In pregnant rats, a small amount of radioactivity passed through the placental barrier. The absorbed radioactivity was rapidly excreted in the bile and entered into enterohepatic circulation. Subsequent excretion of radioactivity was about 90% in urine, less than 7% in feces, about 40% in bile, and less than 1.5% in the expired air within 48 hr. Binding ratio of radioactivity to plasma protein was about 40% and transfer ratio of radioactivity to blood cell was about 30%.