A radioimmunoassay for the quantitation of methadone in biofluids is described. The antiserum was prepared by using an albumin conjugate of N-methyl-N-(1-methyl-3,3-diphenyl-4-oxohexyl)aminoethanol succinate. By employing tritium-labeled dl-methadone as the radioligand and a sample volume of 0.05 ml, the method has a lower limit of sensitivity of 3 ng/ml. The ability of the antiserum to detect methadone was not influenced by the presence of the metabolites of methadone or members of the methadol series. Morphine, codeine, levorphanol, meperidine, l, α-acetylmethadol and d-propoxyphene do not cross-react. After the i.v. administration of 0.90 or 1.5 mg/kg of methadone to male rats, plasma methadone levels decline biexponentially and elimination is independent of dose. The mean volume of distribution is 7.58 ± 0.87 liters/kg; the mean elimination T 1/2 is 88.6 ± 1.9 min and the plasma clearance is 59.3 ± 1.4 ml/min/kg. These results demonstrate that methadone is eliminated by the rat much more rapidly than previously suspected.
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of Pharmacology and Experimental Therapeutics|
|State||Published - 1981|
ASJC Scopus subject areas
- Molecular Medicine