By Bruna Sarri e Jaqueline Pizzaia
Gabapentin, an structural analog of GABA, has primarily used as anticonvulsant but now, used as analgesic adjuvant as well, mainly for chronic and neuropathic pain management in dogs and cats. Despite gabapentin is well known about its efficacy on pain management for humans, there are some concerns about it in veterinary medicine. However, we can already find good information indicating gabapentin as an analgesic adjuvant, like this one from the International Veterinary Academy of Pain Management (IVAPM) .
When does gabapentin work?
The main use of gabapentin is as anticonvulsant in refractory treatments with other drugs or as adjuvant to other anticonvulsants, such as phenobarbital and potassium bromide. However, the analgesic effect, we mean analgesic adjuvant , has been spreading out on pain management in animals.
As an adjuvant, this drug has been useful for pain relief in animals suffering chronic or neuropathic pain from trauma, limb amputation, spinal cord injuries, intervertebral disc disease, CNS tumours, pelvic fractures, nervous tissue incorporation into the sutures, inguinal hernias, syringomyelia and others.
A study found that gabapentin effectively reduced the signs of neuropathic pain in guinea pigs, such as hyperalgesia and allodynia. It was also observed reduction on hyperalgesia in rats suffering nerve injuries and burns given gabapentin, either orally or subdural, may be due to the inhibition of the inflammatory pain transmission.
Gabapentin seems to be able to reduce morphine doses in the postoperative pain management of dogs that underwent mastectomy, but it doesn't exclude the need to use this opioid. In cats, it has been found that long-term treatment with gabapentin may be beneficial on pain relief in traumatic brain injury and musculoskeletal diseases.
When doesn't gabapentin work?
A study, in dogs that underwent forelimb amputation concluded that the use of gabapentin as an analgesic adjuvant, both in the perioperative and postoperative periods, failed to promote pain relief when compared to the dogs that didn't receive this adjuvant.
Another study with dogs underwent intervertebral disc surgery, didn't observe pain relief in patients that received gabapentin compared to those that received only opioids. However, it was found lower pain scores (not statistically) in the gabapentin combination group. This may be due to the fact that acute postoperative pain plays a nociceptive pattern and gabapentin acts as an antihyperalgesic effect, but not an antinociceptive one.
Does gabapentin cause side effects?
Although gabapentin popularity has been growing up on pain management, we must remember that it can trigger some side effects. Therefore, it should be used with caution and always accompanied by a vet doctor.
Clinical trials found side effects in 25% humans given long-term gabapentin, including fatigue, drowsiness and weight gain. However, all those effects gone after stop treatment. Studies have shown similar side effects in dogs and cats, and sedation was the most common sign , followed by ataxia, nystagmus, inappetence, fatigue, weight gain, vomiting and sialorrhea. Thus, it is always important to assess the benefits and side effects of gabapentin, analysing it each situation.
Gabapentin as a sedative for cats?
Apart from the discussion regarding the side effects of the long-term gabapentin use, there is still some concern about its use as a sedative for transporting cats, which has become equally popular in veterinary clinics.
Studies found that doses higher than 20 mg/cat (from 50 mg to 100 mg) caused less aggression and stress on transporting and handling, if given them between 2 to 3 hours before that. However, in one of those studies they observed that a 100 mg/cat dose caused sedation (80%), ataxia (40%), hypersalivation (6.7%) and vomiting (13.3%); effects that can lead the animal doesn't eat for up to a day, increasing the chances of developing lipidosis. Perhaps it is not the best option to calm down the cat for transportation...
We can realise that gabapentin might be a good option as an analgesic adjuvant for patients suffering neuropathic or chronic pain, especially those which don't respond very well to the base treatment.
However, close clinical monitoring must be necessary, assessing side effects, so that they don't be more pronounced than the good ones. Furthermore, animals given long-term gabapentin should undergo a periodic biochemical assessment for monitoring hepatic and renal injuries, especially cats predisposed to the development of chronic kidney disease.
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– Crociolli et al. Gabapentin as an adjuvant for postoperative pain management in dogs undergoing mastectomy. J Vet Med Sci, 77:1011-1015, 2015.
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– Wagner et al. Clinical evaluation of perioperative administration of gabapentin as an adjunct for postoperative analgesia in dogs undergoing amputation of a forelimb. J Am Vet Med Assoc, v. 236, n. 7, p. 751-756, 2010.