Pharmacodynamics and pharmacokinetics of tolfenamicacid in ruminating calves: Evaluation in models of acute inflammation
Injections of mild irritants intradermally (carrageenan, zymosan and dextran) and intracaveally (carrageenan)in a tissue cage model of inflammation were used in studies of the pharmacodynamics and pharmacokinetics of tolfenamic acid administered intramuscularly in calves. Inhibition of serum thromboxane (TX) B2 and inflammatory exudate prostaglandin (PG) E2 were used as indicators of the magnitude and time course of blockade of cyclo-oxygenase isoforms COX-1 and COX-2, respectively. Single doses of 2, 4 and 8mgkg−1 tolfenamic acid partially inhibited irritant-induced rises in skin temperature (non-dose dependently) and skin oedema (dose-dependently). These doses also markedly inhibited serum TXB2 synthesis and the duration of inhibition was dose-related. A dose of 2mgkg−1 tolfenamic acid also attenuated skin temperature rise over carrageenan-injected tissue cages, and markedly inhibited exudate PGE2 synthesis, even though drug penetration into both exudate and tissue cage transudate was limited. Tolfenamic acid pharmacokinetics were characterized by a relatively short tmax (0.94–2.0411), a high estimated Vdarea (1.79–3.20Lkg−1), an estimated ticase 1/2β of 8.01–13.5011 and Clβ of 0.142–0.175Lkg−1h−1. The actions of tolfenamic acid in inhibiting PGE2 synthesis and in attenuating two of the cardinal signs of inflammation (heat and swelling) suggest that a dosage of 2mgkg−1 administered intramuscularly should be effective clinically as an anti-inflammatory agent.