Clinical meaning
Opioid analgesics exert their effects by binding to mu, kappa, and delta opioid receptors in the central and peripheral nervous system, inhibiting ascending pain transmission and activating descending inhibitory pathways. Mu-receptor activation produces analgesia, euphoria, respiratory depression, constipation, and physical dependence. Opioid metabolism occurs primarily in the liver via CYP3A4 and CYP2D6 enzymes, with some metabolites (morphine-6-glucuronide, normeperidine) being pharmacologically active and accumulating in renal impairment, causing neurotoxicity (myoclonus, hyperalgesia, seizures). The principle of double effect ethically permits administering doses sufficient to relieve suffering even if a foreseeable but unintended consequence is hastened death. The palliative care RN titrates opioids using equianalgesic conversion tables, monitors for respiratory depression using the Pasero Opioid-Induced Sedation Scale (sedation precedes respiratory depression), manages opioid-induced constipation with a prophylactic bowel regimen, and supports patients and families through goals-of-care conversations, advance care planning, and the dying process.