A Double Blind Placebo Controlled Crossover Pilot Trial of Sativex With Open Label Extension for Treatment of Chemotherapy Induced Neuropathic Pain
The problem of neuropathic pain:
A recent review has identified a neuropathic pain prevalence rate of 2-3% in the general
population 1. Based on a Canadian population of 30 million, this means that close to one
million Canadians suffer with neuropathic pain. Neuropathic pain is one of the most
difficult types of persistent pain to treat effectively. No more than 50% 2 of patients with
neuropathic pain obtain adequate relief using current treatments. This is related to the
fact that there are numerous pathophysiological mechanisms that contribute to neuropathic
pain. Neuropathic pain is now understood to involve neural responses in which both
peripheral and central mechanisms contribute to the generation of spontaneous pain and
evoked aspects including allodynia and hyperalgesia 3-5, Traditional approaches to
neuropathic pain have involved the use of oral medications as single agents or in
combination (NSAIDs, opioids, anticonvulsants, tricyclic type antidepressants) 6,7.
Unfortunately this approach is often inadequate and accompanied by side effects. New
treatments are needed for management of neuropathic pain
Neuropathic pain associated with chemotherapy:
Neuropathic pain associated with chemotherapy used for treatment of solid tumors (eg.
paclitaxil, vincristine and cis-platin) is particularly resistant to treatment and is a
growing clinical problem as chemotherapeutic regimes grow more successful in extending life.
This type of neuropathic pain is particularly resistant to treatment and contributes to the
overall level of suffering experienced by patients who recovering from cancer treatment with
chemotherapy. There is pre-clinical evidence supporting that cannabinoid agonists may be
helpful for treatment neuropathic pain caused by chemotherapy.
Cannabinoids in treatment of pain:
The potent anti-nociceptive and antihyperalgesic effects of cannabinoid agonists in animal
models of acute and chronic pain, the presence of cannabinoid receptors in pain-processing
areas of the brain, spinal cord and periphery and evidence supporting endogenous modulation
of pain systems by cannabinoids, provide support that cannabinoids exhibit significant
potential as analgesics8-13.
In addition sixteen of 19 randomized controlled trials examining cannabinoids in the
treatment of pain have demonstrated a significant analgesic effect , nine of the positive
trials involved neuropathic pain 14. Several of these trials examined a cannabinoid extract
preparation Sativex15-20 proposed in the current trial.
What is the current standard of care for neuropathic pain caused by chemotherapy?
The current standard of care for neuropathic pain associated with chemotherapy is similar to
that for management of chronic neuropathic pain. The approach consists of an
interdisciplinary active participatory approach to living with incurable pain. This includes
trials of pharmacotherapy (eg. anti-convulsant analgesics, tricyclic antidepressant
analgesics and opioids), therapeutic exercise programs and training in coping strategies
such as pacing and positive self talk. Such an approach is offered at multidisciplinary pain
centres such as the Pain Management Unit (PMU) here at CDHA.
Given the limitations of current best practice, the compelling pre-clinical work supporting
that cannabinoids exhibit anti-nociceptive effects in neuropathic pain and more specifically
in chemotherapy induced neuropathic pain and initial clinical trials supporting that Sativex
exhibits efficacy in other types of neuropathic pain we propose a pilot trial of 30 patient
to evaluate the effectiveness of Sativex in treatment of neuropathic pain caused by
chemotherapy. If there are positive therapeutic effects in the pilot trial, we plan a
subsequent randomized controlled trial.
Endpoint Classification: Efficacy Study, Intervention Model: Crossover Assignment, Masking: Double Blind (Subject, Investigator), Primary Purpose: Treatment
Change in the NRS-PI from baseline to the final week of stable dose treatment)
Patients will titrate the dose to a level where they obtain an analgesic effect without limiting side effects (week 3)
Mary E Lynch, MD
Capital District Health Authority, Canada
Canada: Health Canada