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Methadone (Dolophine) is a synthetic opioid, a compound that is structurally unrelated to the natural opiates but is capable of binding to opioid receptors. These receptor interactions create many of the same effects seen with natural opiates, including analgesia and sedation. However, methadone does not produce feelings of euphoria and has substantially fewer withdrawal symptoms than opiates such as heroin.(1) Methadone is used clinically to relieve pain, to treat opioid abstinence syndrome, and to treat heroin addiction in the attempt to wean patients from illicit drug use.
Metabolism of methadone to inactive forms is the main form of elimination. Oral delivery of methadone makes it subject to first-pass metabolism by the liver and creates interindividual variability in its bioavailability, which ranges from 80% to 95%. The most important enzymes in methadone metabolism are CYP3A4 and CYP2B6.(1-4) CYP2D6 appears to have a minor role, and CYP1A2 may possibly be involved.(1-5) Methadone is metabolized to a variety of metabolites, the primary metabolite is 2-ethylidene-1,5-dimethyl1-3,3-diphenylpyrrolidine (EDDP).(1-4) The efficiency of this process is prone to wide inter- and intraindividual variability, due both to inherent differences in enzymatic activity as well as enzyme induction or inhibition by numerous drugs. Excretion of methadone and its metabolites (including EDDP) occurs primarily through the kidneys.(1,4)
Patients who are taking methadone for therapeutic purposes excrete both parent methadone and EDDP in their urine. Clinically, it is important to measure levels of both methadone and EDDP. Methadone levels in urine vary widely depending on factors such as dose, metabolism, and urine pH.(5) EDDP levels, in contrast, are relatively unaffected by the influence of pH and are, therefore, preferable for assessing compliance with therapy.(5)
Some patients undergoing treatment with methadone have attempted to pass compliance testing by adding a portion of the supplied methadone to the urine.(7) This is commonly referred to as "spiking.'' In these situations the specimen will contain large amounts of methadone and no or very small amounts of EDDP.(7) The absence of EDDP in the presence of methadone in urine strongly suggests adulteration of the urine specimen by direct addition of methadone to the specimen.
Monitoring of methadone treatment for analgesia or drug rehabilitation
Urine measurement of 2-ethylidene-1,5-dimethyl1-3,3-diphenylpyrrolidine is particularly useful for assessing compliance with rehabilitation programs.
The absolute concentration of methadone and its metabolites found in patient urine specimen can be highly variable and do not correlate with dose. However, the medical literature and our experience show that patients who are known to be compliant with their methadone therapy have ratios of 2-ethylidene-1,5-dimethyl1-3,3-diphenylpyrrolidine (EDDP):methadone of >0.60.(6)
An EDDP:methadone ratio <0.090 strongly suggests manipulation of the urine specimen by direct addition of methadone to the specimen.(7)
Urine pH has a considerable effect on the ability to detect methadone, thus 2-ethylidene-1,5-dimethyl1-3,3-diphenylpyrrolidine is preferable for urine measurements.
Urine concentrations of methadone show very poor correlation to serum levels or the amount of drug administered.
METHADONE BY GC-MS
2-ETHYLIDENE-1,5-DIMETHYL-3,3-DIPHENYLPYRROLIDINE BY GC-MS
1. Gutstein HB, Akil H: Chapter 23: Opioid analgesics. In Goodman and Gilman's: The Pharmacological Basis of Therapeutics. 10th edition. Edited by JG Hardman, LE Limbird. New York, McGraw-Hill Book Company, 2001, pp 569-619
2. Eap CB, Buclin T, Baumann P: Interindividual variability of the clinical pharmacokinetics of methadone: implications for the treatment of opioid dependence. Clin Pharmacokinet 2002;41:1153-1193
3. Ferrari A, Coccia CP, Bertolini A, Sternieri E: Methadone-metabolism, pharmacokinetics and interactions. Pharmacol Res 2004;50:551-559
4. Baselt RC: Disposition of Toxic Drugs and Chemicals in Man. Seventh edition. Foster City, CA, Chemical Toxicology Institute, 2005
5. Principles of Forensic Toxicology. Second edition. Washington DC, AACC Press, 2003, pp 385
6. George S, Braithwaite RA: A pilot study to determine the usefulness of the urinary excretion of methadone and its primary metabolite (EDDP) as potential markers of compliance in methadone detoxification programs. J Anal Toxicol 1999;23:81-85
7. Galloway FR, Bellet NF: Methadone conversion to EDDP during GC-MS analysis of urine samples. J Anal Toxicol 1999;23:615-619