Morphine

• For most patients, morphine is the strong opioid of choice

Main indications

• Pain
• Breathlessness

Mechanism of action

• Produces most of its analgesic effects by binding to the mu-opioid receptor within the CNS and PNS

Contraindications and cautions

• Reduced dose/alternative opiate (e.g. afentanyl) in renal failure

Adverse effects

• Constipation
  • Prescribe softener e.g. sodium docusate
• Nausea and vomiting
  • Prescribe anti-emetic e.g. metacloperamide (normally first-line), levomepromazine (broad spectrum for refractory N+V)
• Signs of opioid toxicity: cognitive impairment, delirium, severe sedation, hallucinations, delirium, myoclonus, seizures, hyperalgesia (paradoxical pain)
  • Examples of hallucinations include seeing shadows and spiders out of the corner of their eye
• The classical clinical features of opioid overdose include the triad of respiratory depression, reduced consciousness and miosis

Administration

• Patients should be commenced on a regular oral modified-release morphine preparation, with rescue doses of 'as required' oral immediate-release morphine for breakthrough pain
• The initial oral dose is based on previous medication use, pain severity, and other factors
• The standard 'rescue dose' of morphine for breakthrough pain is usually one-sixth of the regular 24-hour dose, repeated every 2–4 hours as required (up to hourly may be needed)
• If the oral route is unsuitable, alternatives include subcutaneous or transdermal opioids

Continuous subcutaneous infusion