The salts of methadone in use are the hydrobromide (free base conversion ratio 0.793), hydrochloride (0.894), and HCl monohydrate (0.850). Methadone is also regulated internationally as a Schedule I controlled substance under the United Nations Single Convention on Narcotic Drugs of 1961. Methadone clinics
In the United States, prescription of methadone requires intensive monitoring and must be obtained in-person from an opioid treatment program—colloquially known as a methadone clinic—when prescribed for opioid use disorder (OUD). According to federal laws, methadone cannot be prescribed by a doctor and obtained from a pharmacy in order to treat addiction. Because of its long half-life, methadone is almost invariably prescribed to be taken in a single daily dose. At nearly all methadone clinics in the US, patients must visit a clinic to receive and take their dose under the supervision of a nurse. Both patients who are new to methadone treatment and high-risk patients—such as those who are using drugs and alcohol, including cannabis—must visit the clinic daily. However, some clinics close on national holidays and provide doses to patients to take home. Take-home or take-away methadone
After 90 days to six months (depending on the clinic), if patients have met the clinics criteria, they are typically eligible for take-home doses of methadone. Therefore, they may be allowed to take anywhere from one to six days to visit the clinic once or twice weekly instead of every day.
The formulation sold under the brand name Methadose (flavored liquid suspension for oral dosing, commonly used for maintenance purposes) should not be injected either.Information leaflets included in packs of UK methadone tablets state that the tablets are for oral use only and that use by any other route can cause serious harm. In addition to this warning, additives have now been included in the tablet formulation to make the use of them by the IV route more difficult. Chemistry
Detection in biological fluids
Methadone and its major metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP), are often measured in urine as part of a drug abuse testing program, in plasma or serum to confirm a diagnosis of poisoning in hospitalized victims, or in whole blood to assist in a forensic investigation of a traffic or other criminal violation or a case of sudden death. Methadone usage history is considered in interpreting the results as a chronic user can develop tolerance to doses that would incapacitate an opioid-naïve individual. Chronic users often have high methadone and EDDP baseline values. Conformation
The protonated form of methadone takes on an extended conformation, while the free base is more compact. In particular, it was found that there is an interaction between the tertiary amine and the carbonyl carbon of the ketone function (R3N ••• >C=O) that limits the molecules conformation freedom, though the distance (291 pm by X-ray) is far too long to represent a true chemical bond.