This Page Intentionally Left Blank - Int Medical

156 Cancer and tumor pain
existing evidence fails to demonstrate this class’ safety with respect to side
effects such as orthostasis or cardiotoxicity in CTP patients, who often have
significant comorbidities. 19
Anticonvulsants are frequently used as an adjunct for the treatment
of neuropathic CTP. In one trial of 121 patients with neuropathic CTP,
gabapentin (600–1800 mg/day) reduced pain scores to a degree (0.8 units
on a 10-point scale) that was statistically, but not clinically, significant. 21
Overviewing evidence from this and other trials in which gabapentin was
found of some utility in neuropathic CTP, a 2005 Cochrane review concluded
that gabapentin is efficacious for oncologic neuropathy (but not for nonneuropathic
CTP). 22
At least two studies have assessed local anesthetics as adjuvant agents for
neuropathic CTP. Lidocaine (5 mg/kg infused IV over 30 min) has not been
found effective for cancer-related neuropathic pain in two clinical trials (one
was an RCT). 23,24
One trial of mixed-etiology CTP compared phenytoin (50 mg/dose), sublingual
buprenorphine (0.2 mg/dose), and combination therapy with both
agents. The results indicated that addition of phenytoin to the opioid
achieved no significant analgesic benefit. 25
There are inadequate data to support the use of neuroleptics in the treatment
of CTP of various causes. The available evidence is from small studies.
For acute care management of CTP, concerns with side effects currently
outweigh any likely benefit of agents such as olanzapine (studied in doses
of 2.5–7.5 mg/day). 26,27
Among the NMDA receptor antagonists, ketamine has been studied most
extensively (often for neuropathic pain). Results are mixed. In an open-label
trial of PO ketamine (100–500 mg/day) given to patients with refractory CTP
over three to five days, three quarters were found to have pain score improvement
but nearly half had significant unpleasant side effects (e.g. hallucinations,
confusion). 28 Another study of PO ketamine (0.5 mg/kg per dose)
given three times daily had similar results: significant pain reduction with a
high rate of unacceptable side effects. 29 One assessment of IV ketamine
(0.25–0.50 mg/kg per dose) as an adjuvant to morphine found borderline
pain relief efficacy, but a high (60%) rate of emergence symptoms. 30 Another