© 1996 Oxford University Press
research-article |
Preclinical Toxicity Evaluation of Tepoxalin, a Dual Inhibitor of Cyclooxygenase and 5-Lipoxygenase, in Sprague—Dawley Rats and Beagle Dogs1
Departments of Drug Safety Evaluation, The R. W. Johnson Pharmaceutical Research Institute Raritan, New Jersey 08869–0602 *Drug Metabolism, The R. W. Johnson Pharmaceutical Research Institute Raritan, New Jersey 08869–0602
Received October 10, 1995; accepted April 26, 1996
Tepoxalin [5-(4-chlorophenyl-N-hydroxy-1-(4-methoxyphenyl)-N-methyl-1H-pyrazole-3-propanamide] is an orally active anti-inflammatory agent, which inhibits both cydooxygenase and 5-lipoxygenase activities. The oral toxicity of tepoxalin was evaluated in 1- and 6-month rat (up to 50 mg/kg/day) and dog (up to 150 mg/kg bid) studies. In rats, increased liver weight, centrilobular hypertrophy, and hepatic necrosis were observed at dosages 
20 mg/kg/day. Renal changes indicative of analgesic nephropathy syndrome (i.e., papillary edema or necrosis, cortical tubular dilatation) were seen at 15 mg/kg. In rats treated for 1 month, these hepatic and renal effects were largdy reversible after a 1-month recovery period. Gastrointestinal erosions and ulcers were seen in female rats given 40 mg/kg/day for 6 months. Changes in clinical pathology parameters included decreases in red blood cell count, hemoglobin, and hematocrit mean values; elevation in platelet counts; and an increase in prothrombin and activated partial thromboplastin times. Mild increases in alanine aminotransferase, aspartate aminotransferase, and cholesterol were also noted in rats. Decreased erythrocyte parameters, increased leukocyte counts, and decreased total protein, albumin, and/or calcium were noted in some dogs in the 300 mg/kg/day group follo 6 months of dosing. Small pyloric ulcerations were seen at 100 and 300 mg/kg/day dosages for up to 6 months. In both rats and dogs, no accumulation of tepoxalin or its carboxylic acid metabolite was detected in plasma following multiple dosing over a range of 5 to 50 mg/kg/day for rats and 20 to 300 mg/kg/day for dogs. Plasma concentrations of the carboxylic acid metabolite were severalfold higher than those of the parent compound. The no-effect dosages In rats (5 mg/kg/day) and dogs (20 mg/kg/day) were approximately one and six times the ED50 (3.5 mg/kg), respectively, for inhibition of inflammatory effects in the adjuvant arthritic rat without gastric mucosal damage. In terms of severity, the relative lack of gastrointestinal side effects, within the estimated therapeutic dose range, distinguishes tepoxalin from most marketed anti-inflammatory drugs.