July 2022

In this VETgirl online veterinary continuing education blog, we review baclofen toxicosis in dogs and cats. This isn’t a common human prescription medication known by veterinary professionals, but is should be! That’s because baclofen has a very narrow margin of safety and warrants aggressive supportive care and treatment when it is accidentally ingested by dogs and cats.

By Dr. Justine Lee, DACVECC, DABT
Director – Medical / Co-Founder, VETgirl

Baclofen toxicity in dogs

Baclofen (commonly branded as Lioresal) is a muscle relaxant used commonly for people with spinal cord disease, multiple sclerosis, cerebral palsy, and other neurologic conditions. It is most commonly available in 10 and 20 mg tablets.  It works by stimulating GABA receptors and inhibiting release of neurotransmitters (like substance P and glutamate). When accidentally ingested by dogs and cats, baclofen can be quite poisonous due to its rapid onset of action and the severity of clinical signs associated with.

In humans, baclofen toxicosis results in signs of respiratory depression, coma, hypotension, bradycardia, flaccidity, and potential hypertension or tachycardiac. Some of these clinical signs can even been seen as adverse events with therapeutic doses of baclofen.

In veterinary medicine, the use of baclofen used to be recommended in dogs for the treatment of urinary retention (at 1-2 mg/kg orally but please don’t ever use in dogs!) or gastroesophageal reflux; however, its use has fallen out of favor due to its narrow margin of safety.

In the paper “Baclofen toxicosis in dogs and cats: 145 cases (2004‐2010)“, Khorzad et al evaluated 145 cases of baclofen toxicosis in dogs and cats, and found that the overall survival was 83.8%. This is generally considered a lower prognosis as compared to other toxicology studies of common human medications (e.g., 99-100%, including SSRI antidepressants, amphetamines, etc.).

In this large retrospective study, the authors found that almost all of the patients (92%) developed clinical signs, warranting immediate medical therapy due to its potency and narrow margin of safety. Clinical signs of baclofen poisoning in dogs and cats were seen at doses as low as 0.7 mg/kg, while death was reported at doses as low as 2.3 mg/kg.

Pharmacokinetics of baclofen
In humans, the half-life of baclofen is 2-4 hours. Little is known about the pharmacokinetics of baclofen in dogs and cats. In one study (2) evaluating IV baclofen administration in dogs at a single dose of 3 mg/kg, mean distribution and elimination t½ were 11 and 222 minutes. Baclofen has a wide volume of distribution (3), and 80% of the drug is excreted unchanged in the urine, with the remaining is excreted through the biliary system or hepatically metabolized (3). Baclofen also has low protein-binding (30%) (3). While there is no published or established canine lethal dose, the ASPCA APCC database, deaths are estimated to be between 8-16 mg/kg.

Clinical signs
In this study (1), of those dogs and cats patients showing clinical signs from baclofen poisoning, almost 50% (46.7%) showed central nervous system (CNS) signs (including ataxia, vocalization, coma, drowsiness or lethargy), while 26.6% showing gastrointestinal (GI) signs (including vomiting and hyperslivation). A smaller % of dogs showed general malaise, cardiovascular and respiratory signs (including bradycardiac).

Clinical signs in dogs (and less commonly cats, who less commonly ingest human medications) may vary depending on the ingested dose, and can be seen within 30-60 minutes. According to unpublished ASPCA Animal Poison Control Center data, signs can be seen as early as 15 minutes but as late as 7 hours, with a median of 2 hours. Clinical signs include:

    • Sedation
    • Vocalization
    • Ataxia
    • Lethargy
    • Coma
    • Hypoventilation
    • Bradycardia
    • Hypotension
    • Miosis
    • Nystagmus
    • Tachycardia
    • Tachypnea
    • Hypersalivation
    • Nausea
    • Vomiting
    • Urinary incontinence
    • Cyanosis
    • Cardiopulmonary arrest

Treatment for baclofen toxicosis in dogs and cats
Treatment for baclofen poisoning in dogs and cats should include decontamination (if appropriate), intravenous fluid therapy, anti-emetic therapy (to prevent secondary aspiration pneumonia, especially in the face of decreased gag reflex and hypoventilation), anti-convulsant therapy, monitoring (including end-tidal CO2, pulse oximetry), oxygen support, intravenous lipid emulsion (ILE), and in rare cases, hemodialysis, hemoperfusion, and mechanical ventilation.

Knowing that this specific toxicant can result in fatality, rapid diagnosis and treatment is warranted. When in doubt, call the ASPCA Animal Poison Control Center at (888) 426-4435 for 24/7 help.

ASPCA Animal Poison Control Center logo

References:
1. Khorzad, R. , Lee J. A., Whelan M., Brutlag A.G., Martin E.P., Miyahara L.T., et al. 2012. Baclofen toxicosis in dogs and cats: 145 cases (2004‐2010). J. Am. Vet. Med. Assoc. 214:1059–1064.
2. Scherkenbach, L. A. , Coles L. D., Patterson E. E., Cloyd J.C., Krach L.E., and Kriel R.L.. 2014. Pharmacokinetics and pharmacodynamics of intravenous baclofen in dogs: a preliminary study. J. Pharm. Pharmacol. 66:935–942.
3. POISINDEX editorial staff: Baclofen. POISINDEX System, Vol. 100 (B.H. Rumack et al., eds.). MICROMEDEX, Englewood, Colo

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