Pharmacokinetics of grapiprant, a selective EP4 prostaglandin PGE2 receptor antagonist, after 2 mg/kg oral and i.v. administrations in cats.

Drugs that provide effective analgesia in cats are limited. The aim of the study was to assess the pharmacokinetics of grapiprant after 2 mg/kg administration via p.o. and i.v. routes in cats. Six healthy adult cats were used according to an open, single-dose, two-treatment, two-period, randomized cross-over design. Cats were assigned to two treatment groups and administered with 2 mg/kg of grapiprant (pure powder) through p.o. and i.v. administration. Blood samples were collected at preassigned times and analysed by a validated HPLC method. After both administrations, grapiprant concentrations were detectable in plasma for up to 24 hr in five of six animals. The critical parameters including clearance (173.2 ml hr-1  kg-1 , range 120-326 ml hr-1  kg-1 ) and volume of distribution (918 ml/kg, range 611-1608 ml/kg) were calculated from the i.v. group. The mean oral F% was low (39.6% range 31.5%-45.2%). If the assumption that the minimal effective concentration in dogs (164 ng/ml) applies in cats too, grapiprant orally administered at 2 mg/kg might be effective for 10 hr. Further studies are necessary to establish the minimal effective concentration in this animal species.