Opioid toxicity and opioid-induced hyperalgesia in palliative care

At a glance

• Opioid toxicity in palliative care is usually iatrogenic and gradual: renal function falls, a dose is escalated, an interacting drug is added, or pain is relieved by radiotherapy or a nerve block so the same dose is now too much.
• Two pictures overlap. Classical mu toxicity (sedation, miosis, slow breathing) and opioid-induced neurotoxicity (OIN): myoclonus, delirium, hallucinations, allodynia and hyperalgesia.
• Opioid-induced hyperalgesia (OIH) is increased pain sensitivity caused by the opioid itself. Pain becomes diffuse and worsens as the dose goes up.