Codeine Phosphate (Orthopaedic — Mild-Moderate Pain)

How it works

Codeine is a prodrug metabolised by CYP2D6 to morphine, which acts on central mu-opioid receptors to reduce pain perception; it also has a direct antitussive and constipating effect.

Prescribing in practice

• Analgesic response and toxicity depend on CYP2D6 metaboliser status — ultra-rapid metabolisers can develop life-threatening opioid effects, so codeine is contraindicated during breastfeeding and avoided in children and those with known ultra-rapid metabolism.
• Combine with caution with other CNS depressants and CYP2D6 inhibitors, anticipate constipation and the risk of tolerance and dependence with continued use, and avoid in acute respiratory depression or paralytic ileus.
• Use the lowest effective dose for the shortest time and reduce or avoid in significant renal or hepatic impairment per the SPC.

Monitoring

Monitor pain relief, sedation and respiratory status when used in higher or repeated doses, and review bowel function and ongoing need.

Counselling the patient

• May cause drowsiness and constipation; avoid alcohol and do not drive if affected.
• Use only as needed for short-term pain and follow the stated maximum frequency.
• Seek advice before stopping after regular use, as the dose may need tapering.

Evidence & guidelines

MHRA advice restricts codeine for pain in children and during breastfeeding because of the risk of morphine toxicity in CYP2D6 ultra-rapid metabolisers.