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Anesth Analg 1983; 62:705-709
© 1983 International Anesthesia Research Society
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Narcotic Dosage and Central Nervous System Opiate Receptor Binding

Theodore H. Stanley, MD, Josee Leysen, DrSc, Carlos J. E. Niemegeers, DrSc, and Nathan L. Pace, MD

Departments of Anesthesiology and Surgery, University of Utah School of Medicine, Salt Lake City, Utah, and the Departments of Biochemical Pharmacology and Pharmacology, Janssen Pharmaceutica Laboratories, Beerse, Belgium.

Abstract

Increasing doses of lofentanil (0, 0.08, 0.16, 0.31, 0.63, 1.25, 2.50, 5.00, and 10.0 µg/kg), a potent long-acting narcotic, were administered intravenously to rats to examine the relationship among narcotic dosage, degree of analgesia (inhibition of tail withdrawal reflex), anesthesia (no response to bone-crush injury), and central nervous system (CNS) opiate-receptor occupancy (inhibition of [3H] sufentanil binding). Our results demonstrate that increasing doses of lofentanil produce increasing analgesia and anesthesia and eventually complete opiate receptor occupancy. Analgesia occurs with doses of lofentanil (0.31 µg/ kg) that result in levels of CNS opiate-receptor binding too low to be measured and anesthesia occurs with doses of lofentanil (1.25 µg/kg) that produce occupancy of about 25% of the available opiate receptors in subcortical areas and cortex. These findings in rats cannot be applied to narcotic usage in humans, but the data do indicate that in rats a dose eight times the anesthetic dose of lofentanil is needed to saturate virtually all available CNS opiate receptors (10.0 µg/kg). Whether saturation of most or all available CNS opiate receptors during narcotic anesthesia is of clinical importance remains to be determined.

Key Words: ANESTHETICS, Intravenous: lofentanil • ANALGESICS: lofentanil • RECEPTORS: opiate.






Lippincott, Williams & Wilkins Anesthesia & Analgesia® is published for the International Anesthesia Research Society® by Lippincott Williams & Wilkins with the assistance of Stanford University Libraries' HighWire Press®. Copyright 2006 by the International Anesthesia Research Society. Online ISSN: 1526-7598   Print ISSN: 0003-2999 HighWire Press
Copyright © 1983 by the International Anesthesia Research Society.