Methemoglobinemia in Dogs

Methemoglobin is an altered form of hemoglobin in the blood, where there is a change in the state of the iron molecules. This change prevents the hemoglobin from carrying oxygen molecules to the organs and tissues of the dog's body. This process is normal at low levels but can be accelerated by several factors.

Products such as ibuprofen and acetaminophen, widely used by humans, are commonly ingested by dogs. Ibuprofen is rapidly absorbed orally in dogs, while acetaminophen is quickly absorbed from the gastrointestinal tract. The presence of elevated amounts of either drug in the dog's system can cause the onset of methemoglobinemia, a functional anemia brought about by the production of too much methemoglobin. Peak concentrations in the blood are achieved within 30 minutes to three hours, although the presence of food in the stomach can slow the absorption. Metabolized in the liver, the product is excreted in the urine within 24 hours after ingestion. While the sudden, unexpected ingestion of analgesics does occur, the more common cause of analgesic-induced methemoglobinemia is through overuse of the drugs over a period of time. Topical anesthetics such as benzocaine can trigger methemoglobinemia in dogs. Less-common causes for the disease include genetic predisposition and exposure to skunk musk, although these cases are rare.

Anemia patients essentially suffer symptoms associated with low oxygen levels. The most easily recognizable symptom is pale pink, white or even purplish gums. Anemic dogs will have reduced stamina, tiring easily or acting listless. Other symptoms commonly associated with methemoglobinemia include depression, weakness, jaundice, swelling of the face, hypothermia, vomiting and rapid breathing. If your dog is suffering from methemoglobinemia, his blood will appear brown or muddy-colored instead of bright red in a spot test.

If methemoglobinemia is brought about by a sudden overdose of analgesics, treatment may include administering activated charcoal or IV fluids to your dog, oxygen therapy or even a blood transfusion in the most serious case. More often than not, simple discontinuation of the drug will suffice. Dogs living with genetic methemoglobinemia enjoy normal life expectancies and generally no treatment is required. For cases of severe anemia, methylene blue administered via IV will reduce the methemoglobulin count in the blood.

Any dog is susceptible to methemoglobinemia. If you regularly administer an analgesic to your dog for pain relief, remain alert to the signs and symptoms of anemia. If your pet ingests the drugs by accident and you have the opportunity, your vet may recommend that you induce vomiting. A dog who has received methylene blue should have his red blood cell count closely monitored. In any case where methemoglobinemia is suspected, consult your veterinarian immediately. The overall prognosis for most dogs is good, regardless of the causative factors.