Methadone

PHARMACOLOGY

A synthetic opioid and an agonist at the mu and delta receptors. It is also an NMDA antagonist and therefore can be a useful opioid to rotate to in cases of neuropathic pain.

Onset of action: 30 minutes
Time to peak: 90 minutes
Plasma ½ life: 15 -75 h

DOSING

(see Pitfalls/Concerns below)

UNWANTED EFFECTS

  • Cardiac dysrhythmia
  • Hypotension
  • Sweating
  • Constipation
  • Nausea
  • Vomiting
  • Rarely: prolonged QT interval, torsades de pointes

PITFALLS/CONCERNS

The use of methadone in the palliative care setting can be challenging because of its long half life and subsequent accumulation. The appropriate determination of the correct conversion ratios from other opioids can also be problematic. We would advise that its use should only be undertaken with advice from a practitioner with experience in its use. There are also many more drug-drug interactions with methadone compared to other opioids. Caution must be used when adding or stopping other medications.

NOTE

This information is drawn from a number of sources (see below). The reader is encouraged to access these and other relevant literature for more detail. As always, sound clinical judgment should be used in individual clinical cases. In particular, it should be remembered that there may be significant variation in the pharmokinetics of a drug resulting from a number of factors, including the individual patient’s metabolism/disease status and how the medication has been formulated.

SOURCES/REFERENCES

  1. Brunton LL, Lazo JS, Parker KL, editors. Goodman and Gilman’s: the pharmacological basis of therapeutics. 11th ed. McGraw-Hill Professional; 2006.
  2. Twycross R, Wilcock A. Palliative care formulary. 3rd ed. Radcliffe Medical Press Ltd; 2008.
  3. Repchinsky C, editor. Compendium of pharmaceuticals and specialties (CPS): the Canadian drug reference for health professionals. 44th ed. Canadian Pharmacists Association; 2009.
  4. Goldman A, Hain R, Liben S. Oxford textbook of palliative care for children. 1st ed. Oxford University Press; 2006.
Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License