Ultra-low-dose opioid antagonists to enhance opioid analgesia

This article will review decades of science contributing to current interest in opioid excitatory pharmacology. A long history of clinical confusion provided the stimulus for recent, detailed in vivo and in vitro investigations of the neuropharmacologic mechanisms involved in analgesic and hyperalgesic actions of opioid agonists and antagonists. Following the discovery of central nervous system opioid excitatory-hyperalgesic processes in animals, detailed neuronal cell culture experiments established opioid receptor/Gprotein/adenylate cyclase neurobiochemical mechanisms for bimodal inhibitory versus excitatory actions of opioids. Once this novel model was available to explain the cellular mechanisms responsible for the duality of opioid actions, clinical translation of this technology began to emerge, with a primary focus on selective antagonism of opioid excitatory actions with concomitant low-dose opioid antagonists. Encouraging results from recent animal and clinical studies will be discussed as further evidence that therapeutic pain management may be improved through enhancement of opioid agonist analgesia by cotreatment with ultra-low-dose opioid antagonists that selectively attenuate opioid-mediated hyperalgesia.