methadone
Table of Contents
methadone
see also:
- WH methadone flowchart (pdf) - intranet only
Introduction
- an opioid agonist which is well absorbed orally with a long half-life allowing once daily dosing
- developed in Germany during world war II as a synthetic alternative to morphine as morphine was hard to obtain
- introduced in Australia for Rx of heroin dependence in 1964
- pts attend a clinic or pharmacy each day to be given a supervised dose
- detoxification is not required for pts starting methadone
- psychosocial interventions are an important adjunct
- as many as 85% will stay on methadone for 12mths & most require Rx for at least 2 yrs
- pts retained in Rx on a larger dose & for a longer duration generally achieve better results
- optimal dose is 60-100mg/day
- important Rx factors include optimal dosing & the morale of clinic staff
- programs are not available in the NT
Pharmacology
- mu opioid receptor agonist
- NMDA receptor antagonist actions thought to decrease tolerance
- large Vd 4L/kg as widely distributed to tissues which prolongs its half life as it gets secondarily re-distributed
- eliminated mainly by widespread metabolism to metabolites which, along with some methadone, is excreted in urine
- CYP3A4 inducers increase metabolism
- eg carbamazepine and phenytoin
- CYP3A4 inhibitors reduce metabolism and increase clinical effect
- eg. fluconazole, macrolides, antiretrovirals
- half life is extremely variable:
- opiate naive patients have much longer half lives of up to 59hrs
- most patients have half lives of around 30hrs
Adverse effects
- constipation
- sedation
- diaphoresis
- methadone overdose - resp. depression, coma, non-cardiogenic pulmonary oedema, etc
- prolonged QTc and increased frequency of syncope related to the hERG K+ channel 1)
- patients with significantly prolonged QTc should probably be switched to buprenorphine
methadone.txt · Last modified: 2019/01/11 01:35 by 127.0.0.1