Dexamethasone pre-treatment is antipyretic toward polyinosinic: polycytidylic acid, lipopolysaccharide and interleukin 1/endogenous pyrogen.

The effect of intravenously injected dexamethasone on the febrile response of rabbits to Polyinosinic: Polycytidylic acid (Poly I:C), lipopolysaccharide (LPS) and interleukin 1/endogenous pyrogen (IL1/E.P.) was studied. Dexamethasone (1 mg/kg) attenuated the febrile response to Poly I:C (5 micrograms/kg) but only if administered between 0.5 to 2 h before Poly I:C. If it was given after Poly I:C this resulted in a potentiation of the fever. Antagonism of the febrile response to Poly I:C by dexamethasone pre-treatment was dose-dependent and a maximal effect was observed with 3 mg/kg, a higher dose (6 mg/kg) resulted in a lesser effect on the Poly I:C fever. DEX injected alone (0.5-6 mg/kg) did not have any effect on body temperature. Fevers in response to LPS (50 ng/kg) and IL1/E.P. were also attenuated by dexamethasone. It is concluded that Poly I:C, LPS and IL1/E.P. induce fever by a common mechanism which is either directly or indirectly inhibited by dexamethasone.