Increases GABA synthesis but exact mechanism of action not fully understood

Onset of action: 1-3 h
Time to peak: 2-3 h PO
Plasma ½ life: 5-7 h (increases with renal failure)
Duration of action: 8-12 h


  • 300 mg once daily PO, increasing to 600-1200 mg tid
  • 10-30 mg/kg/24h in divided doses tid PO


  • Common: drowsiness, dizziness, fatigue, ataxia, tremor, nystagmus
  • Other: headache, weight gain, nervousness, dysarthria, rhinitis, diplopia, peripheral oedema, constipation


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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