Comparison of in vitro effects of flunixin and tolfenamic acid on human leukocyte and platelet functions.

A study was made to compare the effects of two nonsteroidal antiinflammatory drugs (NSAIDs), flunixin and tolfenamic acid, on the leukotriene B4 (LTB4) production and migration of human polymorphonuclear leukocytes (PMNs) as well as on platelet aggregation and thromboxane B2 (TxB2) production during blood clotting. Tolfenamic acid inhibited LTB4 production in PMNs as well as FMLP- and LTB4-induced PMN migration (IC50 values 23 +/- 3, 39 +/- 11, and 68 +/- 13 microM, respectively), whereas flunixin inhibited these cell functions only with the highest concentration tested (100 microM). On the other hand, flunixin was clearly a more potent inhibitor of TxB2 production and adrenaline-induced platelet aggregation than tolfenamic acid, the IC50 values in TxB2 production being 0.28 +/- 0.02 microM and 2.6 +/- 0.3 microM for flunixin and tolfenamic acid, respectively. We suggest that inhibition of PMN functions may be an additional mechanism in the antiinflammatory action of tolfenamic acid. At least in human PMNs and platelets, flunixin seems to be only an inhibitor of cyclooxygenase.