Makindo Medical Notes

Related Subjects: | Analgesia | Sedation and Analgesia on ITU | Codeine | Dihydrocodeine | Diamorphine | Morphine | Opiates

💉 Key point: Give IV doses slowly and titrate to effect. Monitor respiratory rate and sedation. 💊 Antidote: Naloxone (repeated small IV boluses if needed).

🧠 About

• Diamorphine is a strong opioid analgesic used for acute pain, myocardial infarction, pulmonary oedema, and palliative care.
• It is a semi-synthetic derivative of morphine with greater lipid solubility, allowing faster central nervous system penetration and onset.
• Metabolised to morphine and 6-monoacetylmorphine, both of which are active at the opioid receptor.
• Always check the BNF entry for Diamorphine for latest dosing and contraindications.

⚙️ Mode of Action

• Acts as a potent μ-opioid receptor agonist in the brain and spinal cord, reducing pain perception and emotional response to pain.
• Enhances descending inhibitory pain pathways and reduces neurotransmitter release in the dorsal horn.
• Approximately 1.5× stronger than morphine IV/SC due to higher lipid solubility and CNS penetration.

💉 Indications & Dosing

• Acute pain / pulmonary oedema: 2.5–5 mg slow IV/IM/SC every 4 hours PRN; may increase to 10 mg if no respiratory depression.
• Palliative care (syringe driver): 10 mg SC over 24 hours, titrated as required for comfort and symptom control.
• Often combined with an antiemetic (e.g. Cyclizine or Metoclopramide).

📊 Typical Dose Ranges

⚠️ Interactions

• Avoid with MAOIs (current or within 14 days) — risk of severe CNS and respiratory depression.
• Additive sedation with benzodiazepines, alcohol, or other CNS depressants.

⚕️ Cautions

• Reduce dose in elderly, hepatic impairment, renal impairment, or heart failure.
• Monitor for accumulation in renal dysfunction — active metabolites can cause prolonged sedation.
• Use with care in patients with raised intracranial pressure or compromised respiratory drive.

🚫 Contraindications

• Respiratory depression or acute asthma exacerbation.
• Severe COPD or hypercapnic respiratory failure.
• Head injury or raised intracranial pressure.
• Paralytic ileus, bowel obstruction, or severe hypotension.
• Myasthenia gravis.

💥 Adverse Effects

• Less nausea and hypotension than morphine, but otherwise similar opioid adverse profile.
• Nausea, vomiting, constipation, ileus, sedation, pruritus, urinary retention.
• Respiratory depression, miosis, reduced cough reflex, bradycardia, hypotension.
• Neuropsychiatric: delirium, agitation, seizures (rare).
• Endocrine: decreased libido, hypogonadism, adrenal suppression with chronic use.
• Rare: biliary spasm, rhabdomyolysis, bronchospasm.

📖 Educational Summary

Diamorphine remains widely used in UK hospitals and palliative care settings because of its smooth titratability and rapid onset. Its pharmacokinetic profile makes it especially suited to syringe driver use in end-of-life care. Always titrate to effect rather than fixed schedules, balancing analgesia against sedation and respiratory rate. In practice, morphine and diamorphine are therapeutically interchangeable if equipotent dose conversion is used. Understanding receptor pharmacology and context-specific dosing prevents under-treatment of pain or inadvertent toxicity.

📚 References

• Diamorphine – British National Formulary
• Faculty of Pain Medicine, Opioids Aware (RCoA 2023)
• Palliative Care Formulary, 7th Edition
• NICE NG140: End of Life Care for Adults (2019)