- The clearance half-life of methadone averages 30 hours. Urinary methadone excretion is pH dependent; excretion is decreased with increased urinary pH.
- Patients who are taking methadone for therapeutic purposes excrete both parent methadone and metabolite in their urine.
- The absolute concentration found in a patient’s urine sample can be highly variable; however, patients who are known to be compliant with their methadone therapy have ratios of EDDP:methadone >0.60.
- If there is a question as to a patient's therapeutic compliance, a serum test request for the specific drug of interest may be of help.
- The presence of methadone >LOQ indicates exposure to methadone within 6 to 7 days prior to specimen collection.
- Methadone is metabolized to an inactive metabolite, 2-ethylidene-1,5-dimethyl-3,3- diphenylpyrrolidine (EDDP).
Methadone → 2-Ethylidene-1,5-dimethyl-3,3- diphenylpyrrolidine (EDDP)
Approximate Detection Times
|Methadone||LOQ (ng/mL)||Detection Time* up to|
|EDDP (methadone metabolite)||