Gabapentin For Dogs

In the last decade or so, vets have been prescribing gabapentin for dogs with arthritis, neuropathic or chronic pain …  but many had adverse reactions and were still in pain. Let’s take a closer look at gabapentin in dogs.

What Is Gabapentin?

Gabapentin was developed in 1975 as an anti-seizure medication. It was approved by the FDA in 1993 to treat human epilepsy, and then shingles. 

But Pfizer, the parent company, was illegally marketing the drug for off-label uses that weren’t FDA-approved. Pfizer settled the off-label case in 2004 and paid criminal charges and civil liabilities totaling $430 million. In 2009, pregabalin, a gabapentin derivative called Lyrica, was part of another settlement against Pfizer in the amount of $2.3 billion. The drug was being used off-label and was causing concerns in the medical field. 

Studies showed it induced pancreatic cancer in rats. In humans, there were reports of:

• Dizziness
• Ataxia
• Fatigue
• Tremors
• Involuntary muscle jerking
• Mental distress
• Addiction
• Withdrawal syndrome (confusion, agitation, upset stomach, delirium)

There’s a list of oral gabapentin side effects on the Mayo Clinic’s website. 

And in 2008, veterinarians began prescribing gabapentin, without FDA approval.

What Is Gabapentin Used For In Dogs?

Despite the earlier settlements against Pfizer … in 2008 gabapentin first appeared in a short article in Veterinary Information Network (VIN). It started appearing in the veterinary community and was being prescribed for pain, including pain from intervertebral disc disease, chronic pain associated with arthritis and cancer, and neural and post-operative pain. It’s often prescribed alongside NSAIDs or opiates. It’s thought to amplify their effect on pain management despite potential side effects.                                                               

Veterinarians also prescribed gabapentin for seizures in dogs, anxiety and idiopathic epilepsy. And yet, a 2009 study found gabapentin influences a receptor that helps create new synapses in the brain. Gabapentin can block a specific receptor responsible for making new neuronal connections that help grow, develop and repair the brain. This means that gabapentin can actually inhibit new neural connections from forming and addressing seizures or anxiety.

And dog owners were reporting adverse effects of gabapentin in dogs, similar to those reported in humans. 

Side Effects of Gabapentin For Dogs

Here’s are side effects dog owners have seen:

• Diarrhea with black tarry stools 
• Vomiting
• Change in behavior along with aggressiveness, 
• Signs of dementia, memory loss and confusion
• Low energy, drooling, sedation 
• Mental distress
• Rolling eye movement
• Ataxia including loss of coordination and balance, unsteadiness when walking, tremors
• Loss of appetite
• Gastrointestinal problems
• Increased anxiety or agitation 
• Fluid retention in limbs and extremities
• Failure to reduce or address pain

There have also been serious allergic reactions such as: 

• Difficulty breathing
• Facial swelling including lips and tongue
• Hives

Let’s look a little deeper into gabapentin for dogs.

Is Gabapentin Safe For Dogs?

There are several reasons to be concerned about giving gabapentin to your dog. 

• Use of gabapentin in dogs is not FDA-approved for veterinary use so it’s prescribed off-label. 
• There are no double-blind studies addressing the efficacy and safety of gabapentin in dogs
• The kidneys and liver metabolize gabapentin so dogs with liver or kidney disease shouldn't take it. 
• Pregnant or nursing dogs, or dogs taking antacids, hydrocodone or morphine could have drug interactions.
• Dogs develop tolerance over time … so they need higher doses of gabapentin. As the dose increases, so does the risk of side effects and that means it’s easier to overdose as well.  

Plumb’s Veterinary Drug Handbook has this to say about Gabapentin:

• Observe caution in renal failure or insufficiency.
• Extra-label use in seizures in dogs; “evidence to support use is relatively weak.”
• Extra-label use as an adjunctive analgesic: “Evidence to support use strengthens in recent years … may be effective in some dogs, for chronic pain in dogs with a neuropathic component.”
• As the dose increases, bioavailability decreases.  
• Abrupt discontinuation of the drug has led to withdrawal-precipitated seizures. In humans, it is recommended to wean off the drug when it is used for epilepsy treatment.
• Gabapentin was associated with an increased rate of pancreatic adenocarcinoma in male rats. It is unknown if this effect crosses into other species. 
• The drug is not significantly metabolized and is almost exclusively excreted unchanged into the urine.

Plumb’s Veterinary Drug Handbook offered no confirmation of its effectiveness. Other veterinary articles had additional information about the deficiencies caused by gabapentin. 

• Gabapentin can cause deficiencies in calcium as it works on the calcium channels … not on the neurotransmitter GABA (it was designed to mimic the chemical structure of gamma-aminobutyric acid). 
• It can cause deficiencies in vitamin D, vitamin B1, and folate that contribute to nerve repair.

Gabapentin is a drug that doesn’t have FDA approval or testing in dogs to support its use.

References:

1. Enke O, MBBS MSc et al. Anticonvulsants in the treatment of low back pain and lumbar radicular pain: a systematic review and meta-analysis. CMAJ. 2018 Jul 3; 190(26): E786–E793.
2. Eroglu C et al. Gabapentin receptor alpha2delta-1 is a neuronal thrombospondin receptor responsible for excitatory CNS synaptogenesis. Cell. 2009 Oct 16;139(2):380-92.