Onset of acetaminophen analgesia: comparison of oral and intravenous routes after third molar surgery

Br J Anaesth. 2005 May;94(5):642-8. doi: 10.1093/bja/aei109. Epub 2005 Mar 24.


Background: The purpose of this randomized double-blind study was to compare the efficacy and safety of propacetamol 2 g (an i.v. acetaminophen 1 g formulation) administered as a 2-min bolus injection (n=50) or a 15-min infusion (n=50) with oral acetaminophen 1 g (n=50) or placebo (n=25) for analgesia after third molar surgery in patients with moderate to severe pain after impacted third molar removal.

Methods: All patients were evaluated for efficacy during the initial 6 h period after treatment administration (T(0)) and for safety during the entire week after T(0).

Results: The onset of analgesia after propacetamol was shorter (3 min for bolus administration, 5 min for 15-min infusion) than after oral acetaminophen (11 min). Active treatments were significantly better for all parameters (pain relief, pain intensity, patient's global evaluation, duration of analgesia) than placebo (P<0.05). Adverse events were more frequent after propacetamol, especially pain at the injection site. Propacetamol bolus resulted in a much higher incidence of local adverse events than the infusion (propacetamol bolus 90% vs propacetamol infusion 52%) with no clinically significant benefits in terms of analgesic efficacy.

Conclusion: I.V. propacetamol, administered as a 15-min infusion, is a fast-acting analgesic agent. It is more effective in terms of onset of analgesia than a similar dose of oral acetaminophen.

Publication types

  • Clinical Trial
  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetaminophen / administration & dosage*
  • Acetaminophen / adverse effects
  • Acetaminophen / analogs & derivatives*
  • Administration, Oral
  • Adult
  • Analgesics, Non-Narcotic / administration & dosage*
  • Analgesics, Non-Narcotic / adverse effects
  • Double-Blind Method
  • Female
  • Humans
  • Infusions, Intravenous
  • Injections, Intravenous
  • Male
  • Middle Aged
  • Molar, Third / surgery*
  • Pain Measurement / methods
  • Pain, Postoperative / drug therapy*
  • Tooth Extraction*
  • Tooth, Impacted / surgery


  • Analgesics, Non-Narcotic
  • Acetaminophen
  • propacetamol