title: Time course of naloxone-precipitated withdrawal after acute methadone exposure in humans.
abstract: This study examined naloxone-precipitated withdrawal symptoms from 24 to 168 h after pretreatment with a single 30-mg i.m. dose of methadone in 6 male subjects who were experienced users of opioid drugs but were not currently dependent. The study showed that acute physical dependence signs and symptoms could be reliably precipitated with a small dose of naloxone (0.75 mg/70 kg i.m.) for as long as 96 h (4 days) after a single dose of methadone. The intensity of symptoms at 24 h post-methadone was similar to that observed at 96 h; no precipitated withdrawal effects were observed at 168 h (7 days) after methadone administration. The magnitude of precipitated withdrawal effects at 96 h was not attenuated by the administration of a prior naloxone challenge at 24 h post-methadone. Agonist effects (pupillary constriction; subjective effects) were detectable at 24 h but not at 96 h post-methadone. The results suggest that methadone engenders long-lasting physical dependence effects that can be detected beyond the dissipation of acute agonist effects. Methadone pretreatments may provide a convenient mechanism for the production and examination of long-term mu-opiate receptor physical dependence.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, Baltimore.
authors.forename: M L
authors.initials: ML
authors.lastname: Stitzer
authors.forename: C
authors.initials: C
authors.lastname: Wright
authors.forename: G E
authors.initials: GE
authors.lastname: Bigelow
authors.forename: H L
authors.initials: HL
authors.lastname: June
authors.forename: L J
authors.initials: LJ
authors.lastname: Felch
mesh_terms: D000328:Adult; D001143:Arousal / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008657:Metabolic Clearance Rate / Q000502:physiology; D008691:Methadone / Q000008:administration & dosage / Q000493:pharmacokinetics; D009270:Naloxone / Q000008:administration & dosage*; D009460:Neurologic Examination; D009293:Opioid-Related Disorders / Q000503:physiopathology / Q000534:rehabilitation*; D011957:Receptors, Opioid / Q000187:drug effects / Q000502:physiology; D017450:Receptors, Opioid, mu; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology*
chemical_list: D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D009270:Naloxone; D008691:Methadone