Brain, Behavioral Effects of Duloxetine Observed in Patients with Chronic Low Back Pain

AUSTIN, TX—Initial analysis of the effects of duloxetine vs. placebo in patients with chronic low back pain indicates duloxetine has both brain and behavioral effects in this population, Kevin A. Johnson, of Stanford University School of Medicine, Palo Alto, CA, and colleagues reported during the American Pain Society's 30th Annual Scientific Meeting. These effects were evident on structural MRIs, which indicated changes in gray matter with both duloxetine and placebo, including increases in frontal cortex regions.

The U.S. Food and Drug Administration approved  duloxetine, a serotonin-norepinephrine reuptake inhibitor used for a variety of indications—including depression, diabetic peripheral neuropathy, and fibromyalgia—in November 2010 to treat discomfort from lower back pain.The investigators conducted a randomized, double-blind, placebo-controlled crossover study utilizing clinical assessments to examine the effects of duloxetine and placebo. Additionally, MRI was used to detect possible brain effects of duloxetine and placebo. Patients with at least 6 months of back pain (no radicular symptoms), a minimum pain rating of 4 on a scale of 1-10 for two weeks prior to enrollment, and no current use of pain medication (except acetaminophen) were eligible to enter the study.

Patients were randomized to duloxetine 30mg/day for 1 week, followed by 60mg/day for 5 weeks or matching placebo. Clinical assessments occurred at baseline and at Weeks 1, 2, and 6 of each medication period. Week 6 was the crossover point, where patients were switched to duloxetine or placebo. Additional at-home measures were collected. Clinical measures included basic medical assessments, a battery of pain-related questionnaires, and mood and depression ratings. Data have been collected to date on 18 patients.

A significant change in daily pain ratings was found at the end of the duloxetine period, particularly for patients randomized initially to the placebo treatment group (weekly mean P<0.05 at weeks 3 and 6 for duloxetine vs. placebo and P<0.01 at weeks 4 and 6). Most patients (15/18) had minimal to mild depression (Beck Depression Inventory <19) upon study enrollment; at 6 weeks, no significant increases in overall score were noted in the study. Disrupted sleep patterns and loss of energy were the most frequently rated sub-scale items throughout the study. No significant difference between drug and placebo in overall score was noted on the Brief Pain Inventory. On sub-items, significant improvement was seen with duloxetine in worst pain (P=0.009), least pain (P=0.019), average pain (P=0.007), and current pain (P=0.009).

The investigators concluded that given the large individual variability in pain ratings found within an individual treatment period and in response to a particular treatment, accounting for such individual variability may help refine behavioral and neuroanatomical analysis.