Drug of Abuse, Methadone Screen with GC-MS Confirmation, Urine
Compliance monitoring of methadone therapy in patients being treated for heroin addiction
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Methadone (Dolophine) is a synthetic narcotic with analgesic and pharmacological properties similar to morphine. It can be administered orally and provides analgesia for approximately 24 hours. The I-racemate of the drug is active, while the d-racemate has little activity. Methadone has properties that make it useful for treating heroin addiction. Sedation ensues with higher doses, which is an undesirable side effect. Administered in small doses of 5 to 20 mg, the drug occupies the opioid receptor for prolonged periods of time, blocking the action of morphine, precluding the euphoric effect that heroin addicts seek. Addicts who self-administer heroin while taking methadone doses do not experience euphoria, only sedation, miosis, respiratory depression, hypotension, and dry-mouth. Tolerant patients may require doses up to 200 mg per day.
Methadone is metabolized by demethylation (cytochrome P  2D6 [CyP 2D6]) to 2-ethylidene-1, 5-dimethyl-3, 3diphenylpyrrolidine (EDDP) and to 2-ethyl-5-methyl-3, 3-diphenylpyrrolidine (EMDP). Individuals with genetic deficiencies of CyP 2D6 or coadministered amiodarone, paroxetine protease inhibitor antiretrovirals, chlorpheniramine, or other drugs that inhibit CyP 2D6 will accumulate methadone with associated toxicity.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
EMIT cutoff concentration: 300 ng/mL
Positives are reported with a quantitative GC-MS result.
A positive result derived by this testing indicates that the patient has used methadone in the recent past.
Because the urine output of methadone associated with minimal effective therapy can range between 1,000 to 50,000 ng/mL and only 5% is excreted unmetabolized, there is poor correlation of urine concentration with dose.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Goodman LS, Gillman A, Hardman JG, et al: The pharmacological basis of therapeutics. 9th edition. Edited by JG Hardman, LE Limbird. New York, McGraw Hill, 2001, pp 544-55
2. Baselt RC: In Disposition of Toxic Drugs and Chemicals in Man, 5th edition. Chemical Toxicology Institute, Foster City, CA 2000