Chronic pain is an abnormal state in which there is a “malfunction” of the pain system. Many different factors contribute to this state and some of the abnormalities are in the brain.

There are functional abnormalities ( ie changes in the way the brain works) as well as structural changes.

The normal brain
In the normal brain there are pathways that block the experience of pain. These are decending inhibitory pathways and are influenced by brain hormones such as Serotonin (5-HT) and norepinephrine (NE).

Chronic pain
In chronic pain states, the combined effect of these brain hormones is reduced or lost; shifting the descending pain modulatory system from a state of inhibition towards a state of pain facilitation.

This is often called central sensitisation or pain amplification.

Duloxetine is a medication that maintains normal levels of Serotonin (5-HT) and norepinephrine (NE) in the brain. Theoretically this medication should lower the experience of pain.

A review of duloxetine trials
There has been a recent review of 12 double-blind, placebo-controlled trials of duloxetine in patients with chronic pain (diabetic peripheral neuropathic pain, fibromyalgia, chronic pain due to osteoarthritis, and chronic low back pain).

Patients received duloxetine (60 to 120 mg/day) or placebo.

Results

Average pain reduction :
Compared with patients on placebo, significantly more patients treated with duloxetine reported a moderately important pain reduction (=30% reduction) in 9 of the 12 studies,

Improvement of physical function :There was a minimally important improvement in physical function in 8 of the 12 studies was

Patient global impression of improvement:
A moderately to substantial improvement was demonstratred in 11 of the 12 studies.

Comment:

In a recent article posted in our library the multimodal approach to the management of chronic pain was highlighted.

Medications are part of pain management and this medication does have a place in the treatment protocols. As with all medications, understanding the benefits and the unwanted effects is important in assessing the risks and the benefits of any medication.

As far as the benefits are concerned this review concluded that duloxetine is efficacious in treating chronic pain as demonstrated by significant improvement in pain intensity, physical functioning, and patient ratings of overall improvement.

At this time we are not yet able to determine who will respond to this medication so a trial of therapy is the only way to assess this.