Time to peak: 4-8 h
Plasma ½ life: 8-24 h


  • 100-200 mg once daily-bid, increase by 100-200 mg every 2 weeks
  • Usual maximum dose 800-1200 mg in divided doses
  • Less than 6 years: 10-20 mg/kg/24h in divided doses bid or tid PO
  • Over 6 years: 100 mg once daily PO


  • Drowsiness
  • Headache
  • Unsteadiness on feet
  • Dizziness
  • Nausea and vomiting
  • Many drug-drug interactions with anti-epileptics


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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