METHADONE

Methadone is a synthetic opioid that acts on CNS morphine receptors and peripherally on the gut.

Methadone is too long-acting for clinical use and should be avoided. 

Given repeatedly methadone has a half-life of 1 to 3 days, and cumulates. At a given dose, a steady plasma level may not be reached for 1 to 2 weeks. A small increase in dose can produce a massive increase in plasma level 1 to 2 weeks later. Severe drowsiness and even respiratory depression may therefore occur some days after starting, especially in elderly patients, or in patients taking cimetidine (which inhibits metabolism).

Like morphine, methadone has no ceiling, and the oral dose needed to control severe pain varies from 20mg to 900mg per day. It is 2 times as potent by injection (give half the oral dose). Regular oral doses are 4 times more potent than morphine. If it is used, it should be prescribed on a 12-hourly dosage.

Methadone is too inflexible for routine use, and increasing the dose is difficult because the patient has to be carefully monitored for some time.

Methadone is occasionally useful to control cough in patients already on morphine. The addition of methadone linctus (2mg in 5ml) 5ml to 10ml every 8 hours can sometimes help suppress a dry cough resistant to morphine.

The author and publisher have taken precautions to ensure that the information in this book is error-free. However, readers must be guided by their own personal and professional standards of good practice in evaluating and applying recommendations made herein. The contents of this book represent the views and experience of the author, and not necessarily those of the publisher.