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 25-28 September, 2018 | Singapore
it is imperative that radiographs of affected paws be taken to rule out a bone remnant, a surgically treatable problem. When none is found, neuropathic pain is treated by addressing “wind-up” while concurrently providing analgesia. Analgesics alone are ineffective. Amantadine is used off-label to block the NMDA receptors in the spinal cord, however, because it lacks analgesic effects, an opioid plus NSAID are used concurrently. The regime suggested by Gaynor is outlined in Table 2.
Another condition, feline orofacial pain syndrome
(FOPS) is a disorder of cats with behavioural signs
of oral discomfort and tongue mutilation. There is suggestion that it is inherited in an autosomal recessive manner. It is believed to be neuropathic in nature and characteristically includes exaggerated licking and chewing movements, and pawing at the mouth; in some extreme cases mutilation of tongue, lips and buccal mucosa occurs. It appears to be triggered by mouth movements (grooming, eating)29. Like idiopathic cystitis, it occurs at irregular intervals with the cat appearing to be pain-free in between these episodes. In both, external factors can also influence the disease such as anything causing stress or anxiety as well as other illness29,30.
Therapy for FOPS includes ruling out other causes of facial and oral pain, any dental disease discovered should be treated. An attempt to identify and eliminate environmental stresses and triggers should be made. Pain relief requires multiple agents including NSAIDs plus phenobarbital, carbamazepine, gabapentin or amitriptyline. Treatment is long-term and may not be successful in some cases31.
New mediators of pain have been identified and are being studied as therapeutic targets. These include nerve growth factor (NGF), piprants, neurokinin-1 antagonists, selective neurotoxins and cannabinoids.
• Nerve growth factor
This mediator of inflammatory and neuropathic pain
is elevated in models of chronic and animal pain32. Hyperalgesia is alleviated by inhibition of NGF. Numerous approaches are being evaluated, (e.g., monoclonal antibodies) to negate its effect. Risks and benefits of Tanezumab have been studied in human medicine for interstitial cystitis, osteoarthritis, diabetic neuropathy and post-herpetic neuralgia. A felinized anti- NGF monoclonal antibody (NV-02, Frunevetmab, Nexvet Biopharma) has been developed; multicenter clinical trials are underway33-34.
• Pripants
Pripants and substances that antagonize prostaglandin E2 EP4 receptor, i.e., further down the inflammatory cascade than NSAIDs thereby not interfering with the “housekeeping” actions of COX enzymes. While not yet approved for use in cats, grapiprant (Galliprant®, Elanco) has been studied in this species and has received FDA approval for use in dogs with DJD35.
• Neurokinin-1 antagonists
This class of drug prevents substance P from binding
to NK-1 receptors. Maropitant is typically used as an antiemetic but appears to provide visceral analgesia in dogs as indicated by reduced anaesthetic requirements during ovariohysterectomy.
• Selective neurotoxins
Two selective neurotoxins have been studied in
dogs: resiniferatoxin and substance P-saporin. These selectively inhibit or destroy cells in receptors. It is too early to say whether these will play a role in veterinary analgesia.
• Cannabinoids
The use and benefits of medical marijuana for people
continue to be investigated. Cannabinoids
interact with receptors in the endocannabinoid system. These include cannabidiol (CBD), cannabinol (CBN) and tetrahydrocannabinol (THC) receptors. Fractions that target CBD and CBN receptors (e.g., as in hemp oil) but not THC receptors might be of use; THC is dangerous for small animals. Research is lacking for use for cannabinoids in cats at this time.
Table 1: Analgesic choices for chronic pain in cats

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