Methadone, Serum or Plasma

Serum or plasma

1 mL

0.3 mL

Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.

Therapeutic monitoring of methadone (Dolphine®/Methadose®) treatment.

Methadone can be detected in blood 15 to 45 minutes after oral administration, with peak levels occurring at 2.5 to 4 hours. The elimination of half-life has a mean value of approximately 22 hours (range 5 to 130 hours). Due to interindividual variation of P450 enzyme systems, up to a 17-fold variation in methadone blood concentrations can be found in patients given the same dose.¹

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.

Liquid chromatography/tandem mass spectrometry (LC/MS-MS)

Therapeutic: 100−400 ng/mL

Methadone possesses many of the pharmacologic properties of morphine and is approximately equipotent as an analgesic when administered parenterally. Unlike morphine, however, methadone produces marked sedative effects with repeated administration as a result of drug accumulation. This undesirable property restricted clinical usage of the drug until 1965 when Dole and Nyswander began narcotic maintenance treatment of former heroin addicts using large daily oral doses of dl-methadone.² Whereas maintenance patients may receive as much as 180 mg of the drug daily, doses ≤50 mg have been known to prove fatal to nontolerant adults. The pharmacologic activity is due almost entirely to the l-isomer. The d-methadone isomer does have analgesic properties in large doses and this may be due to conversion to minor amounts of α-l-methadone and α-l-normethadol, both of which are potent analgesics.