Pharmacokinetics of felbinac after intravenous administration of felbinac trometamol in rats

Felbinac trometamol (trishydroxymethylaminomethane 4-biphenylacetate) is a new water-soluble salt of felbinac currently undergoing clinical evaluation as an intravenous (i.v.) formulation for the treatment of severe post-operative pain. This article reports the pharmacokinetics of felbinac after i.v. administration of felbinac trometamol in Sprague-Dawley rats. The maximum plasma concentration (C(0)) and area under the plasma concentration-time curve (AUC) of felbinac administered at doses of 3.36, 8.40 and 21.0 mg/kg felbinac trometamol increased linearly with dose. Felbinac was highly protein bound (~95%) at plasma concentrations up to 75 μg/ml and extensively metabolized with only small amounts being excreted unchanged in urine (0.318%), feces (0.530%) and bile (0.465%). 4'-Hydroxyfelbinac was the principal metabolite in urine, feces and bile together with felbinac glucuronide, 4'-hydroxyfelbinac glucuronide and sulfate. The majority of the administered dose was excreted in urine (63.6%) mostly as 4'-hydroxyfelbinac. Total drug in urine and feces accounted for about 72% of the dose. It would appear that felbinac trometamol has the potential to replace lipid-based NSAID formulations and progress to clinical evaluation.