Anticonvulsants appear to be useful in the management of neuropathic pain and chronic pain with central sensitization. The
anticonvulsant most commonly discussed is gabapentin, a structural analogue of gamma-aminobutyric acid (GABA), which appears
to provide analgesia by modulating both sodium and calcium channels affecting NMDA and perhaps other receptors.2,4,7,9,11,14 While the use of gabapentin for veterinary cancer pain is poorly described in the literature, it is known to be well-tolerated,
highly bioavailable, and rapidly metabolized in dogs, and it appears to work best when used in combination with other analgesic
agents, such as NSAIDs.9,11,14,60 Currently, only anecdotal evidence supports the use of gabapentin for chronic or neuropathic pain relief.
Tricyclic antidepressants have analgesic effects for both nonmalignant pain conditions and for chronic cancer pain in people.1-4,7 This class of drugs includes amitriptyline and the veterinary-approved clomipramine, among others. While the use of tricyclic
antidepressants as adjuvant analgesic agents is still poorly described in veterinary medicine, they appear to be best suited
for combination therapy with other classes of analgesic drugs.1-4,7,9,11,14,61 Their analgesic effects are thought to be attributed to actions on endogenous monoaminergic pain modulating systems, especially
those using norepinephrine and serotonin.2
Synthetic analogues of inorganic pyrophosphate, bisphosphonates are a class of drugs that, by specifically binding to sites
of active bone turnover and inhibiting osteoclasts, can help manage malignant bone pain.1-4,62,63 By directly causing osteoclast apoptosis, bisphosphonates are especially useful to treat painful osteolytic bone lesions.
The more potent intravenous aminobisphosphonates, including pamidronate and zoledronate, are preferred for osteolytic bone
pain from metastatic carcinoma and multiple myeloma in people, and ongoing studies are evaluating their use in dogs and cats
with primary and metastatic bone cancer (Figures 1A & 1B).62,63
Corticosteroids have a mild analgesic effect and can be occasionally considered for cancer pain, especially when inflammation
participates in the ongoing nociceptive stimuli.1,2,4,7,10,11,14 They should not be used concurrently with NSAIDs.
Figure 3. This 13-year-old mixed-breed dog receives acupuncture treatments for osteoarthritis and back pain initially triggered
by lytic lesions from multiple myeloma that is in prolonged complete remission following systemic chemotherapy.
Complementary therapies and rehabilitation medicine
More and more, complementary therapies are being introduced in the therapeutic regimen to treat cancer pain in people and
may be applicable in dogs and cats.1,2,64,65 Such complementary therapies include acupuncture (Figure 3), massage, stretch and manipulation, hydrotherapy (Figure 4), play therapy, superficial heat and cold application, percutaneous electrical stimulation, transcutaneous electrical nerve
stimulation, laser therapy, ultrasound, and pulsed magnetic field therapy.1,2,9,14,64,65 While their specific use for veterinary cancer pain has not been described in the literature, their increasing availability,
anecdotal reported efficacy, and excellent tolerability profile make them an attractive addition to the therapeutic options
in that setting.
Figure 4. An adult German shepherd receiving hydrotherapy on an underwater treadmill. (Photograph courtesy of Dr. Dianne Dunning.)