Methadone Absorption and Distribution:
The rates of absorption and distribution of the drug in the system play a crucial role in determining the length of time it stays within the system. The route of administration influences when the two processes should begin. Through oral ingestion, Methadone in the form of tablets may be detected in the blood within the first 30 minutes to an hour due to the rapid absorption rate of the drug in the gastrointestinal tract. However, the injectable methadone solutions have higher absorption rates that take 15-30 minutes. The distribuation rate of the drug may vary greately from one user to the other depending upon the above quoted factors.
Methadone Metabolism :
Methadone is a lipid soluble drug, so it has the ability to penetrate and cross over into the phospholipid layers of the cells and tissues throughout the body. Once administered, Methadone undergoes extensive biotransformation in the liver and consequently, Methadone is metabolized into two inactive metabolites namely; 2-ethylidene-1.5-dimethyl-3.3diphenylpyrrolidine (EDDP) and 2-ethyl-5-methyl-3, 3-diphenyl-1-pyrroline (EMDP), as well as active minor metabolites such as normethadol and methadol. The inactive metabolites, EDDP and EMDP, are excreted through bile and eliminated in the kidney.
As metabolized Methadone enters into the systemic circulation for distribution throughout the body, its lipid soluble effects may leave drug’s residues in the body. The report by the Substance Abuse & Mental Health Services Administration (SAMHSA) shows that Methadone residues may remain within the system for months after taking the last dose of the drug. Subsequently, these drug residues may exacerbate the withdrawal symptoms and worsen the drug cravings based on the individual’s severity of addiction before starting Methadone treatment.
Overdose or high dosage levels may cause excessive accumulation of methadone in the system whereas too low dosage levels may aggravate the patient’s susceptibility to drug cravings and withdrawal symptom effects.
Most of the major metabolites of methadone are excreted via urine. Small amounts are also excreted via feces, bile and sweat. Though most of the methadone is excreted in the from of its meathbolites, some unchanged methadone may also leave the body via urine. Since the half life of methadone ranges between 8-59 hours, its average half life can be estimated to be 33.5 hours. It means that for the complete removal of the drug, it may take around 8 days.