Methanol poisoning is most commonly seen in pets due to ingestion of windshield washer fluid, however methanol can also be found in cleaning products, varnish, solvents, gasoline and model airplane fuel. Methanol is a colorless alcohol that has a slightly sweet odor. It is also referred to as “wood alcohol.”
Clinical signs of methanol poisoning are typically seen quickly, within 30-60 minutes, and are similar to those seen in pets with ethanol poisoning. Most commonly, the CNS and GI systems are affected; less commonly, cardiovascular, and respiratory effects are seen. Clinical signs may include lethargy, ataxia, depression, vomiting, diarrhea, and abdominal pain. Respiratory failure is less common, and seizures are rare. While methanol poisoning can cause blindness in humans and primates, it is not a side effect seen in dogs and cats.
Well established minimum toxic doses are not available for methanol. Since most windshield washer fluids contain a lower concentration of methanol (generally 20-30% methanol), ingested doses must be calculated accordingly. Most pets ingesting a small amount of methanol may be able to be monitored at home. In the event of a larger ingestion, unknown ingested amount or if a pet is symptomatic, they should be evaluated by a veterinarian as soon as possible. Clinical signs are expected to be rapid, so if an animal is not exhibiting signs within 3-4 hours of suspected exposure, it is unlikely that they will be affected.
A diagnosis of methanol poisoning is typically based on history and clinical signs. In addition to the clinical signs noted above, a physical exam and baseline diagnostics including venous blood gas, blood glucose and blood pressure may show evidence of metabolic acidosis, hypoglycemia, or hypotension. Of note, serum methanol levels are rarely done but do provide an effective measurement of toxicity. Ethylene glycol tests are not effective for testing methanol.
There is no antidote available for methanol poisoning. Due to methanol being rapidly absorbed in the GI tract, emesis is typically not indicated. Due to the rapid onset of CNS signs, emesis should only be considered within 15 minutes of ingestion in an asymptomatic animal. Activated charcoal is not effective since it does not bind to alcohol. Depending on clinical signs, therapy for an affected cat or dog may include intravenous fluids to enhance excretion, blood glucose monitoring with dextrose boluses if needed, GI protectants and antiemetics, rewarming, blood pressure monitoring and anticonvulsant therapy.
If treated early and aggressively, the prognosis for a pet with methanol poisoning is typically good. If a pet is being treated for methanol poisoning after ingesting windshield washer fluid, it is always important to have the owner check the ingredient list as the fluid may also contain ethylene glycol, which can be fatal in pets at even small doses.
Kelly Mahoney, DVM student extern, University of Minnesota, Class of 2022
Heather Handley, DVM, Senior Consulting Veterinarian, Clinical Toxicology