4.1 Cancer-related pain
Cancer-related pain can be severely debilitating. Opioids have
traditionally been the mainstay of pain management in such patients.
However, the somnolence induced by these drugs may sometimes be
unacceptable, with impairment in the child’s quality of life and ability
to communicate. Moreover, tolerance to opioids is a common concern, with
requirements of increasingly higher doses. Ketamine, due to its low
sedation potential and safe hemodynamic profile, has been used as an
adjunct to opioids and is often regarded as second-line therapy after
opioids for intractable neuropathic pain in pediatric oncology practice,
with usual doses ranging from 0.025-0.3 mg/kg/hour.58In pediatric end-of-life care, the role of ketamine patient-controlled
analgesia (PCA) has also been mentioned.59 Low dose
ketamine infusion for refractory pain in children with cancer has been
shown to significantly reduce pain as well as the requirement of opioid
dose.60,61,62 In this regard, the anti-hyperalgesic
and anti-allodynic effect of ketamine has been
well-described.63,64 However, a recent systematic
review found no post-operative opioid-sparing effect of ketamine in
children.65 Epidural ketamine in combination with
morphine has been found to increase the duration of
analgesia.66 Oral ketamine doses ranging from 0.25-1
mg/kg/dose are safe and effective in children with chronic
pain.67 Oral ketamine offers the distinct advantage of
the ease of administration combined with potent analgesic, something
which has so far been achieved satisfactorily only with a handful of
agents. Despite the emerging evidence for ketamine for cancer pain, its
use currently remains largely off-label. World Health Organization (WHO)
has discontinued its guidelines on the pharmacological treatment of
persisting pain in children with medical illnesses (2012) in light of
new evidence and is revising it, but perhaps it would be premature to
list ketamine as an upfront analgesic after opioids for children with
cancer.68 Moreover, ketamine doesn’t find a mention in
WHO guidelines for the pharmacological and radiotherapeutic management
of cancer pain in adults and adolescents (2018), in the absence of
concrete evidence from high-quality studies.69Table 2
provides a summary of the prospective studies of ketamine for cancer
pain in children.