Relationship between paracetamol plasma levels and its analgesic effect in the rat

J Pharm Pharmacol. 1992 Sep;44(9):741-4. doi: 10.1111/j.2042-7158.1992.tb05511.x.


The relationship between plasma levels of paracetamol and its analgesic effect was studied in the rat using a model of pain-induced functional impairment (PIFI). Female Wistar rats received an intraarticular injection of 30% uric acid in the knee of the right hind limb, inducing its dysfunction. Animals then received oral paracetamol at doses of 178, 316 or 562 mg kg-1 and the recovery of functionality over time was considered as an expression of analgesia. Paracetamol plasma levels were determined by HPLC. Results showed that there is a direct relationship between paracetamol plasma levels and its analgesic effect that follows a sigmoidal model according to the Hill equation. The PIFI model appears to be a useful tool to establish pharmacokinetic/pharmacodynamic relationships for non-narcotic analgesics.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetaminophen / blood*
  • Acetaminophen / pharmacology
  • Analgesics / pharmacology*
  • Animals
  • Chromatography, High Pressure Liquid
  • Female
  • Models, Biological
  • Nociceptors / drug effects
  • Pain Measurement
  • Rats
  • Rats, Wistar


  • Analgesics
  • Acetaminophen