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Torbutrol® is an opioid pain reliever. It is FDA approved for pain relief in cats and for chronic coughing in dogs. It is common and accepted to use off label for pain in dogs.
Torbutrol® is not for use in patients with heartworm disease. Use with caution in patients with liver or kidney disease. Contact your veterinarian if you see vomiting, diarrhea, seizures or signs of sedation. Signs of overdose or toxicity include decreased heart rate or decreased respiratory rate. Naloxone is used to treat overdoses. Use with caution when combining with medications that have sedative properties.
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http://www.dodgerslist.com/lit/drugs.html#torbutrol