PHARMACOLOGY
Pro-drug of morphine. Its metabolites bind to the u-opioid receptor providing analgesia. It is about 1/10 as potent as morphine.
Codeine may not provide analgesia if the patient is a poor CYP2D6 metaboliser or if another drug such as paroxetine is acting as a CYP2D6 inhibitor.
Codeine also has antitussive properties and will slow gastro-intestinal motility and is sometimes used in diarrohea
Onset of action: 0.5 to 1 h for analgesia; 1-2 h for antitussive effect
Time to peak effect: 1-2 h
Duration of action: 4-6 h
Plasma ½ life: 2.5-3.5 h
DOSING
Commonly it is given in a compounded preparation with acetaminophen/paracetamol or another agent which may limit its use based on “ceiling dose”
- Analgesia: 30-60 mg q4h PO
- Antitussive: 15-30 mg q4h prn PO
- Diarrhoea: 30-60 mg q4h prn PO
- Children more than 6 months: 0.5-1.0 mg/kg q4h PO (max 60 mg/dose)
UNWANTED EFFECTS
- Common initial: nausea and vomiting, drowsiness, unsteadiness, delirium (transient)
- Common ongoing: constipation, nausea and vomiting
- Occasional: dry mouth, sweating, pruritis, hallucinations, myoclonus
- Rare: respiratory depression, dependence
PITFALLS/CONCERNS
- Causes constipation
- Some individuals (about 7% of Caucasians) are poor metabolisers of codeine and, therefore, unable to achieve a significant analgesic benefit
- Because of some immature metabolic processes codeine may not be appropriate in younger children and infants
NOTE
This information is drawn from a number of sources (see below). The reader is encouraged to access these and other relevant literature for more detail. As always, sound clinical judgment should be used in individual clinical cases. In particular, it should be remembered that there may be significant variation in the pharmokinetics of a drug resulting from a number of factors, including the individual patient’s metabolism/disease status and how the medication has been formulated.
SOURCES/REFERENCES
- Brunton LL, Lazo JS, Parker KL, editors. Goodman and Gilman’s: the pharmacological basis of therapeutics. 11th ed. McGraw-Hill Professional; 2006.
- Twycross R, Wilcock A. Palliative care formulary. 3rd ed. Radcliffe Medical Press Ltd; 2008.
- Repchinsky C, editor. Compendium of pharmaceuticals and specialties (CPS): the Canadian drug reference for health professionals. 44th ed. Canadian Pharmacists Association; 2009.
- Goldman A, Hain R, Liben S. Oxford textbook of palliative care for children. 1st ed. Oxford University Press; 2006.