To date there are few research studies examining opioids in the treatment of SCI pain. There is a substantial body of research investigating the benefits of opioid analgesics in the treatment of non-cancer chronic pain and some of those studies examined the impact of opioids on neuropathic pain. There are no studies employing opioid analgesics in post-SCI pain. Furlan et al. (2006) conducted a meta-analysis of effectiveness and side-effects of opioid analgesics for chronic non-cancer pain. Their meta-analysis found that opioids reduced pain and improved functional outcomes when compared to placebo for both nociceptive and neuropathic pain syndromes. Strong opioids (oxydone and morphine) were significantly superior to naproxen and nortriptyline for pain relief but not functional outcomes. Weak opioids (propylene, tramadol and codeine) did not significantly do better than NSAIDS or tricyclic anti-depressants for either pain relief or functional outcomes (Furlan et al. 2006). The authors found that clinically, only constipation and nausea were significantly more common with opioids. The big concern with opioids is of course addiction or opioid abuse. Unfortunately, as Furlan et al. (2006) notes in their meta-analysis, the existing randomized trials were not designed to evaluate addiction.
Attal et al. (2002) found the intravenous morphine titrated to maximal tolerated dosage, significantly reduced dynamic mechanical allodynia but not necessarily spontaneous or burning pains. Oral opioids remain untested in this population.
Norrbrink and Lundeberg (2009) conducted a double-blind RCT to assess the efficacy of tramadol in 35 SCI individuals diagnosed with at- or below- level neuropathic pain. The authors reported significant differences between the two group pain ratings (p<0.05). Tramadol was also found to be effective in improving anxiety, global life satisfaction and sleep quality in individuals with post SCI pain (p<0.05). However, no significant improvement was seen in pain unpleasantness and depression levels.
Eide et al. (1995) randomly assigned individuals with chronic SCI pain into three groups receiving ketamine hydrochloride, alfentanil (m-opioid receptor agonist) or placebo treatment. The study found alfentanil and ketamine effectively reduced SCI pain compared to placebo treatment (p<0.04, p<0.01); however no difference was seen between the two treatments in overall pain. Alfentanil significantly reduced wind up like pain while ketamine did not.
In a pre-post study, Barrera-Chacón et al. (2010) found oxycodone significantly decreased pain intensity and improved sleep (p<0.001) among individuals experiencing neuropathic pain post SCI. These effects were seen mostly in combination with anticonvulsant treatment.
There is level 1b evidence (from one randomized controlled trial; Attal et al. 2002) that intravenous morphine significantly reduces mechanical allodynia more than placebo.
There is level 1b evidence (from one randomized controlled trial; Norrbrink & Lundeberg 2009) that tramadol is effective in reducing neuropathic pain post SCI.
There is level 1b evidence (from one randomized controlled trial; Eide et al. 1995) that alfentanil reduces overall post SCI pain.
There is level 1b evidence (from one randomized controlled trial; Eide et al. 1995) that alfentanil is more effective at reducing wind up like pain than ketamine.
There is level 4 evidence (from one pre-post study; Barrera-Chacon et al. 2010) that oxycodone and anticonvulsants may be effective in improving SCI neuropathic pain.
Intravenous morphine reduces mechanical allodynia.
Tramadol reduces neuropathic pain.
Alfentanil reduces chronic pain post SCI.
Alfentanil is more effective in reducing wind up like pain post SCI than ketamine.
Oxycodone and anticonvuslants may improve neuropathic SCI pain.