Codeine Phosphate

Codeine - has a low affinity for the μ(OP3)and k(OP2) opioid receptors. It is relatively more effective when given orally than parenterally. It is useful as an anti-tussive and for the treatment of diarrhoea. Side-effects are uncommon and respiratory depression is seldom a problem.This explains its traditional use to provide analgesia for head-injured and neurosurgical patients. Doses 60 mg do not improve analgesic activity but may increase side-effects. 10% undergoes demethylation to morphine – this possibly contributing to the analgesic effect.

Uses:
Mild to moderate pain
Diarrhoea and excessive ileostomy output
Antitussive

Contraindications:
Airway obstruction

Administration:
• Orally: 30–60 mg 4–6 hourly
• IM: 30–60 mg 4–6 hourly

How not to use codeine phosphate:
Not for IV use

Adverse effects:
Drowsiness
Constipation
Nausea and vomiting
Respiratory depression

Cautions:
Enhanced sedative and respiratory depression from interaction with:
• benzodiazepines
• antidepressants
• anti-psychotics

MAOI (hypertension, hyperpyrexia, convulsions and coma)
Head injury and neurosurgical patients (may exacerbate ↑ ICP as a result of ↑ PaCO2) May cause renal failure

Organ failure
CNS: sedative effects increased
Hepatic: can precipitate coma
Renal: increase cerebral sensitivity

Renal replacement therapy:
No further dose modification is required during renal replacement therapy