OBJECTIVES: This study aimed to investigate the effects of intramuscular medetomidine and xylazine on tear flow in healthy cats. METHODS: Five cats each received medetomidine 10, 20, 40 and 80 µg/kg IM; xylazine 1.0, 2.0, 4.0 and 8.0 mg/kg IM; and physiological saline (2.0 ml IM) in a randomised order separated by intervals of at least 1 week. The Schirmer tear test (STT) I was performed in both eyes before and 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 6, 7, 8 and 24 h after each dose. RESULTS: The STT I value decreased significantly at 0.5 and 1.0 h and at 0.75 and 1.0 h in both eyes after administration of medetomidine at 10 or 40 µg/kg. After administration of medetomidine 80 µg/kg, there was a significant decrease in the STT I reading at 0.75, 2 and 3 h in the left eye and 0.75, 1, 2 and 3 h in the right eye. The STT I value decreased significantly at: 0.5, 0.75, 1 and 2 h in the left eye and 0.75 h in the right eye after administration of xylazine 1.0 mg/kg; 0.5, 0.75, 1 and 2 h in the left eye and 0.5, 0.75, 1 and 3 h in the right eye after administration of xylazine 2.0 mg/kg; 0.5, 0.75, 1 and 2 h in both eyes after administration of xylazine 4.0 mg/kg; and 0.5, 0.75, 1, 2 and 3 h in the left eye and 0.75, 1, 2, 3 and 4 h in the right eye after administration of xylazine 8.0 mg/kg. CONCLUSIONS AND RELEVANCE: Both medetomidine and xylazine significantly decreased feline tear flow measured by STT I. Therefore, the ocular surface should be monitored carefully and protected appropriately in cats treated with these sedatives.
