Anti-inflammatory and PG inhibitory effects of phenacetin and acetaminophen

Although acetaminophen and phenacetin do not inhibit PG synthesis when added directly to isolated rat platelets and when given orally, both drugs inhibit carrageenan-induced hindpaw edema--a widely used inflammatory assay method. It does not appear that the anti-inflammatory effects of these non-steroidal drugs (unlike other well-known non-steroidal drugs) can be explained on the basis of PG-synthetase inhibition.