Low-dose amitriptyline improved disability outcomes at 3 months for patients with chronic low back pain but did not improve outcomes in disability, work absences, and pain intensity at 6 months in a randomized trial comparing it against benztropine mesylate; however, researchers say the antidepressant holds promise in being an effective treatment for people with the condition.
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While amitriptyline did not meet the primary endpoint of pain reduction at 6 months, the results showed statistically significant disability improvement and a potential therapeutic effect for the treatment of low back pain (LBP), wrote the study’s first author, Donna M. Urquhart, PhD, of the department of epidemiology and preventive medicine at Monash University, Melbourne, and her colleagues.
“This finding is important given that LBP is the leading cause of disability globally, effective treatments for LBP are limited, and there is currently an epidemic of escalated usage of narcotics, with more than 50% of narcotic prescriptions issued to people with LBP,” Dr. Urquhart and her colleagues wrote in their study, published Oct. 1 in JAMA Internal Medicine.
“Although the improvements in pain intensity, general health, and fear of movement/reinjury at 6 months did not reach statistical significance, they suggest that low-dose amitriptyline may have an effect with a larger sample size,” the investigators wrote. “These findings provide support for large-scale clinical trials, with an escalating dose as required, to determine the treatment effectiveness of amitriptyline.”
Dr. Urquhart and her colleagues performed a double-blinded, randomized, controlled trial of 118 patients with chronic LBP who received either low-dose amitriptyline (25 mg per day) or an active comparator (benztropine mesylate, 1 mg per day) for 6 months. Patients were aged 18-75 years, with chronic LBP without a specific cause for a minimum of 3 months. Outcomes for pain intensity, disability, and work absence were measured via the Visual Analog Scale and Descriptor Differential Scale, Roland Morris Disability Questionnaire, and Short Form Health and Labour Questionnaire, respectively.
At 3-month follow-up, patients in the low-dose amitriptyline group reported less disability, compared with the benztropine mesylate group (adjusted difference, –1.62; 95% confidence interval, –2.88 to –0.36). However, there was no significant difference in the reductions in pain at 3 months between the two groups group (adjusted difference, –1.05; 95% CI, –7.87 to 5.78) or in the trial’s primary endpoint of pain at 6 months (adjusted difference, –7.81; 95% CI, –15.7 to 0.10). There was also no significant difference in disability at 6 months (adjusted difference, –0.98; 95% CI, –2.42 to 0.46).
Similarly, there were no significant differences between groups at 3 months regarding work absence (adjusted difference, 0.86; 95% CI, 0.32-2.31) or work hindrance at 3 months (adjusted difference, 0.78; 95% CI, 0.29-2.08), as well as work absence (adjusted difference, 1.51; 95% CI, 0.43-5.38) and hindrance at 6 months (adjusted difference, 0.53; 95% CI, 0.19-1.51). With regard to adverse effects, there were no significant between-group differences at the 3-month or 6-month follow-up visits in the number of patients who had moderate to severe symptoms at baseline (35% assigned to amitriptyline vs. 41% assigned to benztropine mesylate) or at 6 months (26% vs. 32%, respectively), and the percentage of patients who withdrew from the study was 12% in each group.
The National Health and Medical Research Council supported the study. The authors report no relevant conflicts of interest.
SOURCE: Urquhart DM et al. JAMA Intern Med. 2018 Oct 1. doi: 10.1001/jamainternmed.2018.4222.