Page 58 - BSAVA Guide to Pain Management in Small Animal Practice

5 | Pharmacological treatment of pain

VetBooks.ir cleaned with water. The skin should be allowed animals or children in the household who could
be at risk, and will the client ensure safe and
to dry, the patch applied rmly and covered
with an adhesive dressing. An Elizabethan collar
signed, informed consent from the client. After
may be required to prevent the animal licking or appropriate use of the patch? It is wise to obtain
removing the patch. In the time since most of use, the patch should be removed and folded
the veterinary studies have been published, the inwards while wearing gloves, and returned to
type of patch has been changed from a liquid the practice for appropriate disposal, or the
gel patch to one with the drug contained in an animal should return to the clinic for proper
adhesive matrix. Therefore, it is unknown removal and disposal of the patch.
whether the matrix type patches confer similar
pharmacokinetics in animals. The rate of Remifentanil: Remifentanil is an unlicensed,
absorption from the patch to the skin depends ultra-short-acting full MOP agonist. Its onset
on the surface area of the patch; several si es and duration of action are less than 6 seconds,
are available, and patches may be partially meaning that it is only suitable for intravenous
covered to reduce the surface area in contact infusion, no bolus is required, and the dose rate
with the skin if required. Absorption also is rapidly titratable. The very short duration of
depends on skin perfusion, which is in uenced action is due to its metabolism in plasma by
by factors such as skin thickness, skin and esterase enzymes. The main indication is for
ambient temperature, volaemic status and intraoperative analgesia in patients with liver
degree of vasoconstriction. Care must be taken dysfunction. Since its e ects resolve almost as
if a patient is being actively warmed that the soon as it is discontinued, it is imperative that
patch is not over-warmed as this has been analgesia is provided with another opioid for the
shown to result in high plasma fentanyl postoperative period.
concentrations, with the possibility of over-
sedation and/or severe respiratory depression. Pethidine: Pethidine (meperidine) is a full MOP
he uptake of fentanyl is slow; onset of agonist that has been licensed in dogs and cats
analgesia is about 4 hours in dogs or 1 hours for many years. Because it was originally
in cats and therefore the patch should be developed as an anticholinergic agent, it causes
applied the day before elective surgery, or less bradycardia than other opioids and may be
another means of analgesia provided for the useful in patients whose cardiac output is rate
rst 1 to 4 hours. Variable uptake means that, dependent, for example, paediatric patients or
in some patients, adequate analgesia is not those with cardiac disease. Pethidine causes
achieved with a patch alone, emphasizing the histamine release and should not be
importance of regular pain assessment. administered intravenously. Since it is less
Analgesia can be supplemented with another potent than other opioids, a large volume is
opioid (e.g. methadone) if required and required for intramuscular injection.
multimodal analgesia is recommended. The Intramuscular injection of pethidine is painful.
duration of use of a single patch application is These factors, and its short duration of action
about 7 hours from the time of application, to 1 minutes make it unsuitable for
bearing in mind that adequate analgesic levels providing sustained analgesia, but is it useful as
will not be reached for the rst 1 to 4 hours. a sedative or pre-anaesthetic medication in
Although absorption from the patch declines selected cases. Its metabolite, norpethidine
rapidly after days of use, a used fentanyl (which is renally excreted), can cause central
patch still retains a signi cant amount of nervous system stimulation and seizures. This is
fentanyl, which could be harmful to a human if unlikely to occur except in overdose or in
ingested (Reed et al., 11 . If planning to animals with severe renal dysfunction. Pethidine
discharge a patient with a fentanyl patch can be a contributor to serotonin toxicity (see
attached, careful consideration of the risks textbox later), and should not be used with other
should be made; for example, are there other drugs that increase serotonin concentrations.

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