Opioid analgesics
Opioid analgesics are mu-receptor agonists (morphine, oxycodone, hydromorphone, fentanyl, methadone, tramadol) that are first-line for severe acute pain and for moderate-to-severe cancer pain, started at low immediate-release doses and titrated by a reassessment algorithm. Every scheduled opioid needs a stimulant laxative from day one, morphine is avoided in kidney failure, and dose-dependent overdose risk is managed with morphine milligram equivalent limits, naloxone, and avoidance of benzodiazepines.
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What this article covers
- Overview
Definition: opioid analgesics act on mu, kappa, and delta opioid receptors in the brain, spinal cord, and gut, giving potent analgesia for moderate-to-severe nociceptive pain; the class includes…
- Epidemiology
Cancer pain is common and undertreated: up to 50% of patients receiving cancer therapy and up to 90% with advanced cancer have pain, and about one third receive inadequate analgesia.
- Risk factors
Dose above 90 MME/day: overdose risk is dose dependent and rises significantly above 90 morphine milligram equivalents per day.
- Pathophysiology
Receptor action: presynaptic inhibition of voltage-gated calcium channels reduces glutamate and substance P release; postsynaptic potassium-channel opening hyperpolarizes neurons.
- Clinical features
Analgesia with sedation: sedation and nausea are common at initiation, with tolerance usually within 2 to 7 days.
- Differential diagnosis
Disease progression or a new cancer complication: new or worsening pain with fever, weight loss, bowel or bladder change, or weakness signals infection, recurrence, or malignant spinal cord compression, not tolerance.
- Diagnosis
Establishing the indication: opioid therapy is defined by pain severity on the 0-to-10 numeric scale within the WHO ladder: mild pain gets nonopioids, moderate pain (score 4-6) adds an oral…
- Management
First, start a low-dose immediate-release opioid in the opioid-naive patient, never a long-acting one: oral: oxycodone 2.5-5 mg, morphine 5-7.5 mg, or hydromorphone 2 mg every 4 hours as needed IV…
- Complications
Fatal respiratory depression: the leading cause of overdose death, compounded by benzodiazepines, sleep apnea, or lung disease.
- Prognosis
Undertreatment is the main failure in cancer pain: about one third of patients receive inadequate analgesia; palliative involvement improves quality of life without a decrement in survival.
- Prevention
Prescribe naloxone and overdose education at 50 MME/day or more, and at any dose with a benzodiazepine, substance use disorder, mental health disorder, COPD, or sleep apnea.
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