Comparison of the anti-inflammatory actions of flunixin and ketoprofen in horses applying PK/PD modelling.
A comparative study in horses of the pharmacokinetics (PK) and pharmacodynamics (PD) of 2 extensively used nonsteroidal anti-inflammatory drugs (NSAIDs), flunixin (FXN) and ketoprofen (KTP), was carried out applying PK/PD modelling. To evaluate the anti-inflammatory properties of these drugs a model of acute inflammation, comprising surgically implanted subcutaneous tissue cages stimulated by intracaveal injection of carrageenan, was used. FXN elimination half-life (T1/2 beta) in plasma was 3.37 +/- 1.09 h. However, in exudate a much longer T1/2 beta was obtained (15.99 +/- 3.80 h). Apparent volume of distribution (Vdarea) for FXN was 0.317 +/- 0.126 l/kg and body clearance (ClB) was 0.058 +/- 0.004 l/kg/h. KTP displayed enantioselective pharmacokinetics, the S(+) enantiomer being predominant in plasma, exudate and transudate. T1/2 beta values for R(-) and S(+)KTP were, respectively, 1.09 +/- 0.19 h and 1.51 +/- 0.45 h (plasma) and 19.73 +/- 2.72 h and 22.64 +/- 4.34 h (exudate), respectively. R(-)KTP was cleared more rapidly than the S(+) enantiomer. ClB values were 0.277 +/- 0.035 l/kg/h and 0.202 +/- 0.022 l/kg/h, respectively. FXN and KTP pharmacodynamics was evaluated by determining their inhibitory effects on serum thromboxane (Tx)B2, exudate prostaglandin (PG)E2, leukotriene (LT)B4 and beta-glucuronidase (beta-glu) and intradermal bradykinin-induced swelling. Both drugs produced marked inhibition of serum TxB2 synthesis for up to 24 h, with no significant differences between the drugs. FXN was a more potent inhibitor of exudate PGE2, the EC50 for FXN being lower (P < 0.01) than that for KTP (0.019 +/- 0.010 microgram/ml and 0.057 +/- 0.009 microgram/ml, respectively). Neither drug had any effect on exudate LTB4 concentration. Differences between the 2 drugs were observed for the inhibition of beta-glu, the Emax for KTP being higher (P < 0.01) than for FXN. However, no differences were observed in other PD parameters. Both FXN and KTP inhibited bradykinin-induced swelling. Differences between the drugs were obtained for Emax, which was greater for FXN (P < 0.01) than for KTP. Equilibration half-life (T1/2Ke0) also differed, being much longer (P < 0.01) for FXN than for KTP. PK/PD modelling proved to be a useful and novel analytical technique for studying the pharmacodynamics of NSAIDs, with the advantage over classical in vitro methods that it provides data in the whole animal. By quantifying action-concentration interrelationships through PK-PD modelling, it is possible to shed light on molecular mechanisms of drug action, and establish probable differences in mechanisms of action between structurally similar drugs.(ABSTRACT TRUNCATED AT 400 WORDS)
Department of Veterinary Basic Sciences, Royal Veterinary College, Hatfield, Herts, UK.
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D000208:Acute Disease; D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000493:pharmacokinetics* / Q000494:pharmacology*; D002351:Carrageenan; D003002:Clonixin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D018592:Cross-Over Studies; D015232:Dinoprostone / Q000097:blood; D005122:Exudates and Transudates; D005966:Glucuronidase / Q000097:blood; D006207:Half-Life; D006736:Horses / Q000097:blood / Q000378:metabolism*; D007249:Inflammation / Q000097:blood / Q000139:chemically induced / Q000188:drug therapy; D007660:Ketoprofen / Q000493:pharmacokinetics* / Q000494:pharmacology*; D007975:Leukotriene B4 / Q000097:blood; D008297:Male; D008954:Models, Biological; D013929:Thromboxane B2 / Q000097:blood
D000894:Anti-Inflammatory Agents, Non-Steroidal; D007975:Leukotriene B4; C014557:flunixin; D013929:Thromboxane B2; D002351:Carrageenan; D007660:Ketoprofen; D005966:Glucuronidase; D015232:Dinoprostone; D003002:Clonixin