Postoperative
pain control is a critical aspect of the care of surgical patients in
veterinary medicine. Many drug types are available for postoperative analgesia
such as opioids and non-steroidal antiinflammatories. Tramadol, a synthetic
opioid, is a widely used analgesic in humans and has become popular for
clinical use in dogs. It is an oral medication usually given at a dose of 2-4
mg/kg every 8-12 hours. It is frequently combined with a non-steroidal
anti-inflammatory, such as carprofen, for postoperative analgesia. Side effects
of tramadol include sedation, nausea, constipation, and seizures. Tramadol
therefore is not recommended for dogs with seizure disorders.
Metabolism
Tramadol
is metabolized by the liver to form O-desmethyltramadol,
or the M1 metabolite.(1) This metabolite is also an active form of the drug. Pharmacokinetic
studies have found that oral administration of tramadol results in adequate
blood levels of the drug and its metabolite.(1)
Efficacy
Although
rapidly gaining widespread use after introduction to the veterinary market,
efficacy studies of the analgesic properties of tramadol have been slow to materialize.
One study from several years ago separately evaluated morphine and tramadol for
postoperative analgesia after ovariohysterectomy in dogs.(2) Using multiple
parameters to evaluate pain, both drugs were found to be effective. In another study, tramadol was compared
to codeine and ketoprofen for analgesia after maxillectomy or mandibulectomy in
dogs.(3) All drugs, including tramadol, were found to provide effective postoperative
analgesia.
Conversely, more recent studies have found tramadol to
compare poorly to other standard analgesics for postoperative pain. Carprofen
was more effective than tramadol for postoperative pain in a series of dogs
having enucleation.(4) Pain scores were monitored and dogs receiving tramadol
were more likely to require rescue analgesics than those receiving carprofen.
In another study, after TPLO for ruptured cruciate in 30 dogs, those that
received firocoxib orally, alone or in combination with tramadol, had lower pain scores,
lower rescue opiate administration, and greater limb function than dogs that received only tramadol.(5) Tramadol was also not
effective in providing analgesia in an experimental study using an acute pain
model in Beagles.(6)
These studies create a mixed and confusing message to
veterinary clinicians about the efficacy of tramadol. Inherent to all pain
studies is the difficulty in making objective assessments of postoperative pain
in dogs, but well controlled studies using accepted methods of pain scoring
should provide useful information. The conflicting results of clinical and
experimental studies make it clear that tramadol alone as a postoperative
analgesic may not provide the expected level of analgesia. This appears to be
particularly true after procedures associated with high pain levels, such as in
dogs having major orthopedic surgery.
Conclusions
Even in view of the studies showing lack of efficacy, tramadol’s
advantages make it an attractive choice for postoperative analgesia. It is
administered orally, is well tolerated by most dogs, and is felt by many
clinicians to be a reasonable alternative for dogs in which NSAIDS are
contraindicated. We routinely use tramadol in combination with carprofen for
postoperative analgesia in dogs. In our clinical experience that combination
provides effective analgesia even after orthopedic procedures such as TPLO.
Tramadol alone is prescribed in those dogs that cannot take NSAIDS since there
are few alternatives and tramadol is certainly better than no analgesic
treatment.
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References
1. KuKanich, B. and
Papich, M. G. (2004), Pharmacokinetics of tramadol and the metabolite O-
desmethyltramadol in dogs. Journal of
Veterinary Pharmacology and Therapeutics, 27: 239–246.
2. Mastrocinque, S.
and Fantoni, D. T. (2003), A comparison of preoperative tramadol and morphine
for the control of early postoperative pain in canine ovariohysterectomy. Veterinary Anaesthesia and Analgesia,
30: 220–228.
3. Martins TL1, Kahvegian MA, Noel-Morgan
J, Leon-Román MA, Otsuki DA, Fantoni DT.
Comparison
of the effects of tramadol, codeine, and ketoprofen alone or in combination on
postoperative pain and on concentrations of blood glucose, serum cortisol, and
serum interleukin-6 in dogs undergoing maxillectomy or mandibulectomy. Am J Vet Res. 2010
Sep;71(9):1019-26.
4. Cherlene Delgado, DVM, Ellison Bentley, DVM, DAVCO, Scott Hetzel, MS, and Lesley J Smith, DVM, DACVAA. Carprofen provides
better post-operative analgesia than tramadol in dogs after enucleation: A randomized,
masked clinical trial. J Am Vet Med Assoc. 2014 December 15;
245(12): 1375–1381.
5. Davila D1, Keeshen TP,
Evans RB, Conzemius
MG.
Comparison of the
analgesic efficacy of perioperative firocoxib and tramadol
administration in
dogs undergoing tibial plateau leveling osteotomy. J Am Vet Med Assoc. 2013 Jul 15;243(2):225-31.
6. Kogel
B, Terlinden
R, Schneider J. Characterisation of
tramadol, morphine and tapentadol in an acute pain model in Beagle dogs. Vet Anaesth
Analg. 2014 May;41(3):297-304
