Page 70 - BSAVA Guide to Pain Management in Small Animal Practice

5 | Pharmacological treatment of pain

VetBooks.ir Other routes achieved only with pre-incisional administration
Chahar and Cummings, 1 ; Viscusi et al.,
Other commonly used routes of administration
14; oshi et al., 1 ; Aratana, 16; Lascelles
for local anaesthetics are intra-articular,
intrapleural and intraperitoneal. hile there is and irkby Shaw, 16 .
little concern in terms of systemic toxicity after
intra-articular administration, the absorption Intravenous lidocaine
rate from the pleural and peritoneal space is Unlike other local anaesthetics, lidocaine can
signi cant, resulting in potentially toxic be safely administered as an intravenous
concentrations if large doses are administered. infusion due to its limited toxicity, at least in
In cats, intraperitoneal administration of mg dogs. In cats, the margin of safety is smaller;
kg bupivacaine . did not result in systemic therefore, there is a greater risk of side e ects.
toxicity with peak plasma concentration hile its use as an antiarrhythmic or its role in
occurring minutes after administration, and ischaemic reperfusion injury and shock are not
had an elimination half life of approximately the subject of this handbook, intravenous
hours, suggesting that this dose and route of lidocaine infusion can be used to provide
administration for bupivacaine may be safe, at perioperative analgesia in the hospitalized
least in the presence of a normal peritoneum. animal. Lidocaine s e cacy in treating
The major concern after intra-articular neuropathic pain has been reported in humans
administration is chondrotoxicity. Studies in since the 198 s, in particular to treat post
humans have demonstrated that this risk is herpetic, diabetic and chemotherapy-induced
signi cant for repeated administrations and neuropathy. Its e cacy is supported by a
infusions, while it is less clinically relevant after Cochrane review (Kranke et al., 1 . he most
single administration. In vitro studies have plausible mechanism of action of lidocaine in
demonstrated dose- and time-dependent this setting is the blockade of sodium channels,
chondrotoxicity for all local anaesthetics. A reducing ectopic ring of damaged nerves and
study in dogs has demonstrated chondrotoxicity neurons. In ured bres and neurons are more
for both lidocaine and bupivacaine after single sensitive to lidocaine at low doses because of
administration with steroids in the shoulder joint the characteristic upregulation of sodium
(Aguirre et al., 1 ; i Salvo et al., 14, 1 ; channels observed after the injury. The
Sherman et al., 1 . response to lidocaine administration may be
variable, depending on the type of sodium
Liposomal bupivacaine channel that is upregulated, as lidocaine is
A liposomal bupivacaine formulation has been more e ective in blocking tetrodotoxin resistant
licensed by the US Food and Drug sodium channels compared with tetrodotoxin-
Administration for use in dogs undergoing sensitive ones, with the former being mostly
cranial cruciate surgery. Liposomal bupivacaine upregulated in nerves after injury. The analgesic
has been licensed for use in humans since 11, and minimum alveolar concentration (MAC)
as a single dose local in ltration analgesic sparing e ect of systemic lidocaine has been
techni ue. After in ltration in soft tissues at the demonstrated in the dog, although currently
end of surgery, bupivacaine is slowly released there are no systematic studies investigating its
from the vesicular liposomes, resulting in e cacy in treating neuropathic pain syndromes,
sustained analgesia for several days. In practical and the current evidence is limited to case
terms this is equivalent to continuous infusion reports, expert opinion, and the known e cacy
of local analgesics using a wound soaking in human beings. Unfortunately, the use of
catheter, but without the possible catheter- intravenous lidocaine infusions to treat
related complications. This method of neuropathic pain is limited to the hospital
administration does not allow the exploitation of setting; until a few years ago, mexiletine was
one of the most relevant advantages of local available as an oral alternative to continue
anaesthesia: preventive analgesia, which can be therapy at home in dogs that had a positive

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