Methadone administration routes

Methadone has been used for intrathecal administration. Although this route can provide prolonged analgesia, the adverse effects have been reported to be unacceptable (SEDA-16, 81). 

OPIOIDS MEXILETINE 1. Absorption of oral mexiletine is 1 by co-administration with morphine or diamorphine 2. Methadone may t mexiletine levels 1. Uncertain but thought to be due to an opioid-induced delay in gastric emptying 2. Methadone inhibits CYP2D6-mediated metabolism of mexiletine 1. Watch for poor response to mexiletine consider starting at a higher or using the intravenous route 2. Monitor PR, BP and ECG closely watch for mexiletine toxicity... 

Opiates are widely used all over the world, but recently concerns about opiate use (and deaths from such use) have increased in Australia and the UK (45). The rate of opiate overdose deaths in these countries increased dramatically between 1985 and 1995. Throughout that period, it was four to ten times higher in Austraha than the UK, but the rate of increase may have been greater in the UK in the latter half of the period, since the difference in rate narrowed substantially during that time. Methadone maintenance treatment, estabhshed in Australia in 1969 and in the UK in 1970, has become the main treatment for opiate dependence in both countries. About half of the opiate deaths in the UK were attributed at least in part to methadone. By contrast, considerably fewer (18%) opiate overdose deaths in Austraha were attributed to methadone. The authors suggested that the discrepancy in the rates between the two countries could be artefacts of the differences in (a) the documentation of these deaths, (b) the rate of opiate dependence, (c) the route of opiate administration, (d) opiate purity, and, most importantly, (e) the method of delivery of methadone maintenance treatment. 

Methadone is rapidly absorbed after all routes of exposure. When administered orally, methadone is approximately one-half as potent as when given par-enterally. Oral administration results in a delay of the onset, a lowering of the peak, and an increase in the duration of analgesic effect. It is metabolized primarily in the liver where it undergoes N-demethylation. Protein binding is 85%. Urinary excretion of methadone and its metabolites is dose dependent and comprises the major route of excretion only in doses exceeding 55 mg day It is excreted by glomerular... 

The outstanding properties of methadone are its analgesic activity, its efficacy by the oral route, its extended duration of action in suppressing withdrawal symptoms in physically dependent individuals, and its tendency to show persistent effects with repeated administration. Miotic and respiratory-depressant effects can be detected for more than 24 hours after a single dose, and on repeated administration, marked sedation is seen in some patients. Effects on cough, bowel motility, biliary tone, and the secretion of pituitary hormones are qualitatively similar to those of morphine. 

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