Makindo Medical Notes

💊 Pethidine (Meperidine) is a short-acting opioid analgesic used for moderate to severe pain, particularly in acute settings such as labour. ⚠️ Respiratory depression is the major risk in overdose — presenting with coma, shallow breathing, and pinpoint pupils. Management includes airway support and ventilation, and reversal with naloxone if required.

📘 About

• Always check the BNF entry for full dosing and safety advice.
• Historically used for acute pain and obstetric analgesia, but now largely replaced by morphine and oxycodone due to adverse metabolite accumulation.
• Active metabolite norpethidine (nor-meperidine) has neurotoxic and pro-convulsant properties, especially with repeated dosing or renal impairment.

⚙️ Mode of Action

• Agonist at μ-opioid receptors → inhibits transmission of nociceptive impulses in the CNS.
• Also has weak antimuscarinic effects → less miosis, but may cause tachycardia.
• Suppresses medullary respiratory centres at high doses.

💊 Dose Range

You must always check the BNF or product datasheet for current recommendations.

🔄 Interactions

• Enhanced CNS depression with alcohol, benzodiazepines, or sedating antihistamines.
• Serotonin syndrome risk if used with SSRIs, MAOIs, or linezolid.
• See BNF for comprehensive list.

⚠️ Cautions

• Monitor for respiratory depression and ensure naloxone is available.
• Use extreme caution in renal or hepatic impairment (risk of norpethidine accumulation → seizures).
• Avoid prolonged use in labour — risk of neonatal respiratory depression.
• May worsen delirium in frail older adults due to antimuscarinic and CNS effects.

🚫 Contraindications

• Coma or respiratory failure / hypoventilation.
• Severe hepatic impairment.
• Concurrent MAOI therapy (hypertensive crisis or serotonin toxicity).
• Raised intracranial pressure or head injury — masks clinical signs.
• Paralytic ileus.

💥 Adverse Effects

• Nausea, vomiting, constipation, dry mouth.
• Respiratory depression (dose-dependent).
• Dizziness, sedation, confusion, hypotension.
• Neurotoxicity (tremor, seizures) due to norpethidine accumulation.
• Urinary retention, pruritus.

🧠 Teaching Note

Pethidine’s use has declined because its metabolite norpethidine can cause seizures and delirium, especially in renal impairment. Modern practice favours morphine or diamorphine for acute pain, reserving pethidine only for specific indications (e.g. rigors or shivering post-anaesthesia or transfusion). Always balance analgesic benefit against respiratory and CNS risks.

📚 References

• BNF: Pethidine Hydrochloride
• NICE NG193: Chronic pain (2021)
• UKCPA Handbook of Perioperative Medicines

🕓 Revisions

• 2025-10 — Expanded and annotated by Dr O’Kane (Makindo edition).