Page 316 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

294 PART III Therapeutic Modalities for the Cancer Patient

a
TABLE 16.5 Suggested Dosages of Analgesics to Alleviate Chronic Cancer Pain in Cats —cont’d
Drug Dosage (mg/kg) Notes
VetBooks.ir PSGAGs (polysulphated 5 mg/kg subcutaneously twice weekly There is no clinical evidence that it provides any effect; however, anecdotal infor-
for 4 weeks; then once weekly for
glycosaminoglycans)
mation suggests improvement can be seen after a few injections.
(Adequan) 4 weeks; then once monthly (other
suggested regimens call for once
weekly injections for 4 weeks, then
once monthly)
Robenacoxib 1–2 mg/kg q24hrs Recently gained approval in the EU and other countries for long-term adminis-
tration to cats for chronic musculoskeletal disorder pain. It is the first NSAID
that is a coxib, has a short half-life, and demonstrates tissue selectivity.
Tolfenamic acid 4 mg/kg PO q24hrs for 3 days maxi- Has not been evaluated for chronic pain, but recent objective measurements
mum demonstrated analgesia in the cat when administered perioperatively.
Tramadol 1–2 mg/kg once to twice daily Recent evidence suggests it may be effective for chronic pain in the cat. Tablets
are very bitter and aversive to cats.
Transdermal fentanyl patch 2–5 μg/kg/hrs The patch may provide 5–7 days of analgesia in some cases and should be left
on for longer than 3 days. After removal, the decay in plasma levels is slow.
Vedaprofen 0.5 mg/kg q24hrs for 3 days Has not been evaluated for chronic pain but was evaluated for controlling
pyrexia in upper respiratory infection and for controlling postoperative pain
after ovariohysterectomy.

a None of these drugs have been evaluated for efficacy in the treatment of cancer pain. None of these drugs are approved or licensed for use in chronic cancer pain. Some drugs are approved for
inflammatory or painful conditions in the cat in certain countries, and dosages for the control of cancer pain are extrapolated from these. The dosages given come from the authors’ experience, and the
experience of others working in the area of clinical cancer pain control.
GI, Gastrointestinal; NSAIDs, nonsteroidal antiinflammatory drugs; PO, oral.

The choice of NSAID predominantly depends on the patient’s (BDXL) repeats evaluations after 2 to 4 weeks and then at 1- to
response (closely evaluated both by the veterinarian and by the 4-month intervals as dictated by the individual patient and client.
owner). Currently, limited evidence is available in small animal If pain relief with NSAIDs is inadequate, a comprehensive
medicine on the incidence of adverse events in patients prescribed multimodal therapeutic plan can be established. A common first
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NSAID therapy, 83,84 and most of what we know is related to additional option among veterinarians seems to be tramadol ;
administration to dogs with OA. Veterinary professionals (includ- however, the recognized analgesic effect of tramadol has been
ing veterinary surgeons and nurses) more commonly associate questioned in clinical efficacy studies of chronic pain in dogs, with
side effects with postoperative use of NSAIDs rather than chronic conflicting results. Acetaminophen or acetaminophen/codeine
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administration in dogs. 82 combinations often can be used in conjunction with NSAIDs, but
Unfortunately, pain treatment in cats has not evolved to an the influence of this combination on adverse events is unknown.
equivalent maturity in scientific and clinical analysis, and a con- Other agents that are used to treat chronic pain include aman-
sequent suboptimal analgesic efficiency currently exists in the tadine, an N-methyl d-aspartate (NMDA) antagonist; anticon-
management of felines. 85,86 Emesis, anorexia, lethargy, renal insuf- vulsants (e.g., gabapentin); and tricyclic antidepressants (e.g., as
ficiency, dehydration, and death have been observed after the use amitriptyline). These can all be combined with NSAIDs, although
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of oral NSAID formulations in cats. Moreover, no NSAIDs have we do not know the full extent of side effects. Readers are cau-
been licensed in North America for long-term administration in tioned that they should not assume that combinations of different
cats, and two NSAIDs, meloxicam and robenacoxib, have been adjunctive drugs are without side effects; quite the contrary, there
approved in the European Union only for long-term treatment is much to be learned about potential adverse interactions, espe-
of musculoskeletal pain. However, a number of these compounds cially in cancer patients that may be on other therapies.
probably can be used safely (see Table 16.5). The key to safe
chronic administration of an NSAID in cats is to use the smallest Piprant NSAIDs
effective dosage and avoid using it (or use a reduced dosage) in cats Grapiprant is a highly selective EP prostaglandin PGE receptor
2
4
with renal insufficiency. Another factor the author (BDXL) con- antagonist, a member of the piprant class of NSAIDs. In experi-
siders important is to select drugs with a short half-life to mini- mental settings, this drug has shown antiinflammatory function in
mize the likelihood of adverse toxicities. models of acute and chronic inflammation in rodents. 89,90 Recently
The patient on NSAIDs must be monitored for toxicity. grapiprant was approved by the US Food and Drug Administra-
The owner should be informed of the potential for toxicity and tion (FDA) as a veterinary drug for chronic OA pain in dogs. The
the signs to watch for (lethargy, depression, vomiting, melena, recommended clinical dosage for canine OA pain is 2 mg/kg given
increased water consumption). Blood work (and urinalysis) orally (PO). The advantage of this drug may be the wide safety
should be performed regularly to monitor renal and liver function. margin (see Table 16.4). 91,92 In cats, no adverse events have been
Baseline health panels (complete blood count and serum chemis- associated with oral administration of grapiprant in toxicokinetic
try) should be obtained when therapy is started, and these param- analyses (15 mg/kg, PO, once daily for 28 days), but no studies
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eters should be monitored on a regular basis thereafter. The author have been performed to evaluate the efficacy of grapiprant for the