Hydrocodone Metabolism
- Hydrocodone is metabolized to hydromorphone by conversion of a methoxy group (-OCH3) to a hydroxyl group (-OH) by CYP2D6.
- It is also metabolized to norhydrocodone by demethylation by CYP3A4.
- Hydromorphone undergoes further metabolism, which will be discussed separately.
Hydrocodone has a half-life of about 4 hours and can be detected in the urine up to 3 days after ingestion.
Interpretation
- Both hydrocodone and hydromorphone will be detected in the urine of patients taking hydrocodone.
- If hydromorphone is detected at a concentration less than 30% of the concentration of hydrocodone, the hydromorphone is probably the result of the metabolism of hydrocodone and not separate use of hydromorphone.
- Hydromorphone has a significantly longer half-life than hydrocodone. Therefore, as time increases from ingestion of the drug, the ratio of parent to metabolite will get lower and lower until eventually none of the parent remains in the urine and only a small concentration of metabolite remains. For this, reason, hydromorphone alone may be detected at low concentrations if it has been several days since ingestion.
