Competes with histamine for H1-receptor sites on effector cells in the gastrointestinal tract, blood vessels and respiratory tract; blocks chemoreceptor trigger zone, diminishes vestibular stimulation and depresses labyrinthine function through its central anticholinergic activity

Onset of action: 15-30 minutes
Plasma ½ life: 3.5 h


  • 50-100 mg q4-6h PO/IV, maximum 400 mg/day
  • 5 mg/kg/24h divided into q4h or q6h PO/IV


  • Slight to moderate drowsiness/sedation, headache, dizziness
  • Anticholinergic effects: constipation, dry mouth, blurred vision, urinary retention
  • Paradoxical CNS stimulation


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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