An opioid analgesic with several actions qualitatively similar to those of morphine although the two drugs may act on different opioid receptors

Onset of action: 20-30 minutes
Time to peak: 1-1.5 h
Duration of action: 3.5 h
Plasma ½ life: 4-6 h


  • Starting dose in opioid naïve adult: 2.5 to 5 mg q6h prn and then titrate (see morphine titration in Pain section)
  • Starting dose in opioid naïve children: 0.2 mg/kg q6h and then titrate (see morphine titration in Pain section)

For conversion to morphine and other opioids see Equianalgesic Tables


  • Lightheadedness
  • Pruritus
  • Constipation
  • Nausea
  • Vomiting
  • Dry mouth
  • Drowsiness
  • Rarely hypotension
  • In overdose: respiratory depression


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.


  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.
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