Page 75 - BSAVA Guide to Pain Management in Small Animal Practice

BSAVA Guide to Pain Management in Small Animal Practice

VetBooks.ir Antidepressants multimodal therapy approach athews, 8;
Cashmore et al., 9; oore, 16 . he
Antidepressants are often used as part of
pharmacokinetic study has even raised the
multimodal analgesia in the management of
chronic, neuropathic and persistent pain, in uestion that the current dose 1 mg kg
orally 1 4h may be too low, considering the
some cases with good results (Mehta et al., rapid metabolism of this drug by dogs.
1 ; oore et al., 1 . Although in principle TCAs should be
The antidepressant most used in veterinary
medicine to manage pain is probably e ective in the treatment of painful syndromes
with a strong neuropathic component, for
amitriptyline, a tricyclic antidepressant (TCA), example, in ammatory bowel disease, feline
despite not being licensed for use in dogs and interstitial cystitis, spinal cord injuries,
cats. The veterinary TCA licensed for use in traumatic peripheral nerve injury,
dogs is clomipramine, which shares most of the syringohydromyelia, neoplastic nerve injury
pharmacological properties that may be
relevant to pain management. and paraneoplastic neuropathies and diabetic
TCAs with tertiary amine structure neuropathy, no large trials have been
(amitriptyline and clomipramine) inhibit published to support their e cacy in treating
reuptake of noradrenaline and serotonin, but these conditions in small animals.
they are also mild NMDA antagonists, Possible side e ects of CAs are sedation,
antimuscarinics, voltage-gated sodium channel tachycardia and, at very high doses,
blockers, alpha 1 adrenergic receptor and 1 arrhythmias. It is paramount to avoid using TCAs
histamine receptor antagonists, and activate in concomitance with drugs that a ect the
descending inhibitory pathways. They also serotoninergic system, in particular tramadol, as
inhibit the NF-κB pathway, which is involved in the combination could precipitate serotonin
promoting and maintaining neuroin ammation toxicity (see ‘Serotonin toxicity’).
(Lenkey et al., 6; Rahimi et al., 1 ; Steroids
Zychowska et al., 1 . Clomipramine is more
e ective in promoting serotonin reuptake. heir lucocorticoids are powerful anti in ammatory
mechanism of action on nociception can be drugs, and thus e ective in treating
explained in many di erent ways. Interestingly, in ammatory pain. lucocorticoids bind to a
most of the pathways involved in neuropathic, dedicated cytoplasmic receptor, then
chronic and persistent pain are a ected by translocate to the nucleus, where they cause
tertiary amine TCAs, which makes these drugs upregulation or downregulation of
very interesting in this setting. glucocorticoid-responsive genes. Their
Amitriptyline 1 mg kg orally 4h has anti in ammatory action is mainly due to
been shown to be an e ective treatment for inhibition of the activity of phospholipase A
severe recurrent idiopathic cystitis in cats, likely (mediated by increased transcription of
in part because of the behavioural e ects, but lipocortin), and therefore of prostaglandins
also because of the e ect on neuropathic pain, production, but suppression of other pro-
as this condition is a well known visceral pain in ammatory mediators and non genomic
syndrome, and the direct e ect of increasing mechanisms also play an important role (Rhen
bladder capacity by relaxing bladder smooth and Cidlowski, ; Ayroldi et al., 1 .
muscles via stimulation of alpha adrenergic The role of glucocorticoids in perioperative
receptors estropp and Bu ngton, 4; analgesia has been investigated in humans,
Chew et al., 16 . with particular emphasis on the risk of side
Despite the pharmacokinetics of e ects versus potential bene ts. Administration
amitriptyline having been well characterized in of a single dose of glucocorticoid
dogs (Norkus et al., 1 a; 1 b , there are dexamethasone .1 . mg kg has not been
only case reports relating to its use in a clinical associated with increased risk of infection or
setting to treat neuropathic pain, within a delayed wound healing, and provided variable

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