Protein binding and in vitro serum thromboxane B2 inhibition by flunixin meglumine and meclofenamic acid in dog, goat and horse blood

lunixin was highly protein bound in the serum of dogs (92.2 per cent), gents (84.8 per cent) and horses (86.9 per cent). Meclofenamic acid was also highly protein bound, although there were larger differences between the extent of the binding in dogs (90.3 per cent), goats (84.7 per cent) and horses (99.8 per cent). Both flunixin and meclofenamic acid were potent inhibitors of the in vitro generation of thromboxane (Tx) B-2 in blood. Flunixin inhibited the generation of TxB(2) by 50 per cent of the maximum response (IC50) in dog, goat and horse blood at concentrations of 0.10, 0.02 and 0.04 mu M respectively and by 100 per cent (Imaw) at 2.07, 0.14 and 2.07 mu M respectively. The IC50 values of meclofenamic acid in dogs, goats and horses were 0.77, 0.80 and 0.30 mu M respectively and the Imax values were 3.93, 3.63 and 3.56 mu M respectively. When the concentrations of flunixin were corrected for protein binding, it was estimated that the IC50 of the unbound fractions in dogs, goats and horses were 0.008, 0.003 and 0.005 mu M, respectively. Similarly corrected values for meclofenamic acid were 0.075. 0.122 and 0.001 mu M respectively.