Potential acute hepatic injury in 2 cats exposed to topical human diclofenac

Two domestic shorthair cats from the same household developed acute liver injury with exposure to human transdermal diclofenac cream. A 7-year-old spayed female cat (Cat 1) was brought to the Western College of Veterinary Medicine (Saskatoon, Saskatchewan) with anorexia, lethargy, and fever. The cat had markedly elevated ALT (10 549 U/L) and glutamate dehydrogenase (1456 U/L), and hyperbilirubinemia (total bilirubin: 16.7 μmol/L). Cat 1 improved with supportive care and was discharged. The following day, a 6-year-old spayed female cat (Cat 2) was presented with anorexia and lethargy. Laboratory tests also showed severe hepatocellular injury (ALT: 20 838 U/L, glutamate dehydrogenase: 2054 U/L) and hyperbilirubinemia (total bilirubin: 26.7 μmol/L). A blood smear revealed green to dark-blue cytoplasmic material in neutrophils, consistent with "critical green inclusions" in humans. Cat 2 developed progressive clinical deterioration and was euthanized. The caregiver reported having used 10% diclofenac cream for 3 mo. Drug screening via liquid chromatography-mass spectrometry detected diclofenac in both cats (30 μg/mL in Cat 1, 42 μg/mL in Cat 2). The toxic threshold of diclofenac in cats is currently unknown. Although direct evidence linking acute liver injury to diclofenac exposure was lacking in this case, the report does highlight the potential risk to pet cats whose owners use topical diclofenac. Key clinical message: Topical NSAID formulations such as diclofenac are commonly used by pet owners to treat human pain. The risk to pets, particularly smaller animals exposed to human skin upon which transdermal medication has been applied, remains unknown. Pet owners should be made aware of the potential risks these products pose to animals. Also, to the authors' knowledge, this is the first case report to describe "critical green inclusions" in a cat with severe liver disease.