Factors influencing the inhibitory action of anti-inflammatory drugs on carrageenin induced oedema.

1. In a series of experiments carried out over 2(1/2) years, the inflammatory response of the rat hind paw to injected carrageenin was relatively constant, but the anti-inflammatory activity of phenylbutazone was subject to wide variation.2. Phenylbutazone, aspirin and indomethacin were all well absorbed after oral administration, and the resultant plasma drug concentrations were closely similar to those produced when the drugs were administered intraperitoneally.3. The anti-inflammatory effect of the drugs on carrageenin oedema was variable and poorly correlated with log dose and plasma concentration.4. There was a pronounced and linearly correlated increase in the anti-inflammatory activity of phenylbutazone with increasing ambient temperature in the range 5-30 degrees C.5. Variations in relative humidity at constant temperature (20 degrees C) did not influence the anti-oedema potency of phenylbutazone.6. For the precise evaluation of anti-inflammatory activity in carrageenin oedema tests, it is concluded that accurate control of temperature is essential.