Opioid analgesics

Abstract

Opioid analgesics represent a major therapeutic approach to pain management but challenge clinicians and healthcare systems for appropriate usage and long-term patient benefits. Opioids can be full agonists and partial agonists- antagonists for therapeutic effects that involve the mu, kappa, and delta opioid receptors. Opioids can be administered by different routes that include intravenous, intramuscular, oral, sublingual, transdermal, nasal spray, and rectal suppositories. Opioids can be short-acting and medium-acting agents based upon their elimination half-life that requires multiple daily dosing regimens. Sustained-release formulations have been developed for several opioids. The transdermal formulation allows for once- daily application. Some opioids are metabolized by the CYP enzyme system, while other opioids are primarily metabolized via glucuronidation. Depending upon the opioid, these agents are metabolized to active metabolites that possess analgesic effects that can be greater than, equal to, or less than the parent drug. Morphine has been the prototypical opioid analgesic agent and its pharmacokinetic and pharmacodynamic profile extensively studied in various patient populations. Besides their therapeutic analgesic effects, opioids can produce a variety of adverse effects related to their pharmacokinetic and pharmacodynamic actions that includes physical dependence, tolerance, respiratory depression, cardiovascular effects, sedation, cognitive impairment, gastrointestinal effects, histamine effects, and miosis. An integrated pharmacokinetic-pharmacodynamic approach to opioid treatment can lead to its optimal pharmacotherapy.