Effect of Nalorphine and Levallorphan on Brain Concentrations of Levorphanol in the Dog. ∗

Abstract

Summary

Simultaneous administration of 2 mg/kg of either nalorphine or levallorphan with C¹⁴-labeled levorphanol, 2 mg/kg? in the dog results in a marked diminution of brain concentrations of levorphanol as compared with control. On the other hand, the antagonist drugs did not alter significantly the plasma levels of the levorphanol. The most satisfactory explanation at present is a local brain effect, intra-cerebral vascular, physical-chemical at the molecular level reducing passive membrane penetration, or alteration of an active metabolic process. The phenomenon is not characteristic of all narcotic analgesics, the nalorphine-morphine result being a noted exception.