See the DrugPatentWatch profile for codeine
Where does the body metabolize codeine?
Codeine is metabolised mainly in the liver. The key enzyme is CYP2D6, which converts codeine into morphine (the metabolite responsible for much of codeine’s opioid effect). Other enzymes (especially CYP3A4 and CYP2B6) form additional metabolites, including norcodeine and codeine-N-oxide.
Which organs handle codeine metabolism vs elimination?
The metabolic step happens primarily in the liver. After metabolism, metabolites are then cleared mainly through the kidneys into the urine (with some elimination through bile/feces depending on the specific metabolite).
What happens in people with different CYP2D6 activity?
How much codeine becomes morphine depends on CYP2D6 activity:
- Poor metabolisers produce less morphine, so effects may be weaker.
- Ultrarapid metabolisers produce more morphine, which can increase the risk of opioid toxicity (for example, excessive sedation or breathing problems), especially with higher doses or in children.
What should patients and prescribers watch for?
Because codeine is metabolised to morphine via CYP2D6, anything that changes CYP2D6 activity can change effects. Common examples include drug–drug interactions (some medicines inhibit CYP2D6) and genetic differences in CYP2D6.
Sources
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