Opioid Analgesic (Weak) Pregnancy: Avoid prolonged use especially near delivery — neonatal withdrawal syndrome, neonatal respiratory depression

Codeine Phosphate

Brand names: Codeine (generic)

Adult dose

Dose: 30–60 mg every 4–6 hours as needed

Route: Oral or IM

Frequency: Every 4–6 hours PRN

Max: 240 mg/day

Prodrug — converted to morphine by CYP2D6. Ultra-rapid metabolisers: risk of opioid toxicity. Poor metabolisers: minimal analgesia. Step 2 WHO analgesic ladder.

Paediatric dose

Dose: 0.5 mg/kg

Route: Oral

Frequency: Every 4–6 hours PRN

Max: Do NOT use in children <12 years (MHRA 2013) or post-tonsillectomy/adenoidectomy in children <18 years

Concentration: 25 mg/5 mL linctus mg/ml

MHRA contraindication: codeine must NOT be used in children <12 years for any indication, and must NOT be used in children aged 12–18 years after tonsillectomy/adenoidectomy for obstructive sleep apnoea.

Dose adjustments

Renal

Reduce dose or increase interval in renal impairment — active metabolite (morphine-6-glucuronide) accumulates

Hepatic

Caution in hepatic impairment — reduced CYP2D6 conversion, altered morphine metabolism

Paediatric weight-based calculator

Patient weight (kg)

Clinical pearls

MHRA 2013 contraindication in children <12 years: fatalities reported in ultra-rapid CYP2D6 metabolisers
Not recommended as first-line cough suppressant in children — use alternative where possible
In adults: if no analgesia from codeine, consider CYP2D6 poor metaboliser — switch to tramadol or direct opioid
Prolonged use beyond 3 days for acute pain increases dependence risk — review need at each prescription

Contraindications

Children <12 years (MHRA contraindication)
Post-tonsillectomy/adenoidectomy in <18 years with OSA
Respiratory depression
Ultra-rapid metabolisers (genetic testing rare in practice — clinical vigilance)

Side effects

Constipation (most common)
Nausea/vomiting
Sedation
Dizziness
Respiratory depression (at high doses or in ultra-rapid metabolisers)
Dependence with prolonged use

Interactions

CNS depressants — additive sedation
MAOIs — avoid (serotonin syndrome risk)
CYP2D6 inhibitors (paroxetine, fluoxetine) — reduce conversion to morphine (reduced analgesia)
Alcohol — increased CNS depression

Monitoring

Pain scores
Bowel function
Signs of respiratory depression
Dependence indicators with prolonged use

Reference: BNFc; BNF; MHRA Drug Safety Update Nov 2013; WHO Pain Ladder. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

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