Emergency treatment with intravenous infusion of methylene blue followed by oral administration in a cat presented with severe recurrent methemoglobinemia.

Objective: To describe the use of IV infusion followed by oral administration of methylene blue (MB) to successfully treat recurrent methemoglobinemia (MetHb) in a young cat.

Case Summary: A 6-month-old male Ragdoll cat presented with recurrent episodes of severe MetHb and was successfully managed with IV infusion of MB followed by a course of oral MB. Although the definitive cause of the patient's MetHb remains unknown, the cat made a full recovery following treatment without developing any significant side effects secondary to therapy and at the time of writing not had any further recurrences. Follow-up at 6 months found the patient in good health and without any long-term consequences.

New Information Provided: To the authors' knowledge, this is the first report of a cat presented with severe MetHb quantitatively assessed via co-oximetry and successfully treated with both IV and oral administration of MB.