Neuropathic pain is caused by damage of the somatosensory nervous system leading to abnormal neural excitability. Patients often describe it as ‘burning’, ‘tingling’ or ‘shooting’ down a nerve distribution, or allodynia where they feel pain from non-painful stimuli like air or light touch on skin. Approximately 10% of the general population has neuropathic pain.
There are numerous non-opioid adjuvant medications and analgesic-based interventions available to patients with neuropathic pain, but these are associated risks and side-effects. Only a minority of patients with neuropathic pain experience a clinical benefit from one analgesic intervention and require multi-modal therapies.
Although tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors and anti-epileptic drugs are considered by experts to be first-line analgesics for neuropathic pain, opioids are often considered as second or third-line agents for patients or as a co-analgesic when prompt pain relief during titration of a first-line medication is required.
Strong opioids (i.e. oxycodone
, and morphine
) at doses ranging from 15-240 mg oral morphine equivalents (OMEs) reduce neuropathic pain by at least 33% from baseline. These strong opioids were found to have a number-needed-to-treat (NNT) of 4.3 after 4-12 weeks of treatment and a number-needed-to-harm (NNH) of 11.7. Constipation, somnolence, delirium, dizziness, and dry mouth are the most commonly reported adverse effects of opioids. Maximum effectiveness was associated with 180 mg OMEs/day, with no additional benefit for higher doses.
Despite the fact that opioids are not first-line agents for most patients with neuropathic pain, studies suggest they have efficacy when prescribed as monotherapy or part of a multi-modal regimen for patients with refractory, function-impairing neuropathies, especially when prognosis is short. A ceiling effect has been observed when opioids are prescribed for neuropathic pain and the benefit of increasing the opioid dose for beyond 180-240 mg/day should be pursued only on an individual patient basis.
Adapted from Huang L., Khakimova D. Opioids for neuropathic pain. Palliative Care Network of Wisconsin. Fast facts and concepts #363. Internet. Accessed on December 27, 2018