It most probably acts by inhibiting prostaglandin synthesis in the CNS and perhaps also by blocking pain-impulse generation peripherally. In addition, it acts centrally on the hypothalamus to produce peripheral vasodilatation resulting in an anti-pyretic effect.

Onset of action: 15-30 minutes
Time to peak: 40-60 minutes
Duration of action: 4-6 h
Plasma ½ life: 2-4 h


  • 650-1000 mg q4-6h to a maximum of 4 g per day PO
  • Under 1 year: 10-15 mg/kg q4h/prn PO
  • 1-5 years: 120-250 mg q4h PO
  • 5-12 years: 250-500 mg q4h PO (maximum of 75 mg/kg/day)


  • Rash
  • GI upset
  • Rarely hepatotoxicity and nephrotoxicity


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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