Pharmacokinetic and pharmacodynamic properties of tolfenamic acid (TA) in calves were determined in serum and fluids of inflamed (carrageenan administered) and non-inflamed subcutaneously implanted tissue cages after intramuscular administration both alone and in combination with marbofloxacin (MB). MB significantly altered the pharmacokinetics of TA: mean values were Cmax = 2.14 and 1.64 microg/mL, AUC = 27.38 and 16.80 microg.h/mL, Vd(area)/F = 0.87 and 1.17 L/kg, and ClB/F = 0.074 and 0.128 L/kg/h, respectively, after administration of TA alone and TA + MB. T(1/2)K10 and MRT were not significantly different for the two treatments. The pharmacodynamic properties of TA were not influenced by MB co-administration, in spite of the alterations in some TA pharmacokinetic parameters. TA inhibited prostaglandin E2 (PGE2) synthesis in vivo in inflammatory exudate by 50-88% for up to 48 h after both TA treatments. Inhibition of synthesis of serum thromboxane B2 (TxB2) ex vivo ranged from 40 to 85% up to 24 h after both TA and TA + MB. From the derived pharmacokinetic and eicosanoid inhibition data for TA, pharmacodynamic parameters for serum TxB2 and exudate PGE2 inhibition expressing efficacy (Emax = 78.1 and 97.5%), potency (IC50 = 0.256 and 0.265 microg/mL), sensitivity (N = 1.96 and 2.29) and the pharmacokinetic parameter equilibration time (t(1/2)K(e0) = 0.695 and 24.0 h), respectively, were determined. In this model TA was a nonselective inhibitor of cyclo-oxygenase (COX) (COX-1:COX-2 IC50 ratio = 1.37). TA, both alone and co-administered with MB, did not affect leucocyte numbers in exudate, transudate or blood. Partial attenuation of skin temperature rise over inflamed tissue cages and reduction of zymosan-induced skin swelling were recorded after administration of TA and TA + MB with no significant differences between the two treatments. These data provide a basis for the rational use of TA in combination with MB in calf medicine.