Peripheral polyneuropathy secondary to nitrofurantoin administration in an adult cat

A 6-year-old castrated male domestic shorthair cat was referred because of a 5-day history of walking with a crouched hindlimb stance. Before referral, the cat had been recovering from perineal urethrostomy surgery, preceded by 6 wk of recurrent urinary tract infections, with 3 urinary blockages during that interval. The cat was being managed on nitrofurantoin (4 mg/kg, q8h), prescribed by the referring veterinarian and administered for only 1 d before the perineal urethrostomy surgery. Two days after the nitrofurantoin was restarted, the cat began displaying the crouched hindlimb stance. At the time of presentation for the crouched hindlimb stance, the cat had been administered nitrofurantoin (4 mg/kg, q8h) for a total of 6 d (1 d before the surgery and 5 d at home in between the 2 veterinary visits; however, the medication was not administered in hospital during either visit). Ambulatory paraparesis with no ataxia, decreased patellar reflexes, and decreased medial (digit 2) withdrawal reflexes were present in both hind limbs, consistent with a peripheral polyneuropathy affecting the femoral nerves. Computed tomographic imaging of the thoracic and lumbar spine showed no abnormalities compatible with the clinical signs. A presumptive diagnosis of peripheral polyneuropathy secondary to nitrofurantoin administration was made. Key clinical message: Although peripheral polyneuropathy is a reported side effect of nitrofurantoin, there are only isolated reports of its occurrence in humans and, to the authors' knowledge, no reported cases in companion animals. This case report focuses on the minimally reported neurologic side effects associated with nitrofurantoin administration in companion animals.