Chronic pain treatments more effective when taken together

People suffering from chronic, debilitating pain caused by nerve damage or disease report better pain relief at lower doses of a combined drug treatment than from either drug administered individually, a new Queen’s study funded by the Canadian Institutes of Health Research (CIHR) shows.

When given a combination of the anti-seizure drug gabapentin and the opioid morphine, patients with two different types of neuropathic pain experienced lower pain intensity than when they received either of the drugs individually. As well, significantly lower doses of gabapentin and morphine were required during combination treatment than during treatment with either drug alone.

“We now have the first clinical evidence that combining these drugs provides better pain relief, with comparable side effects,” says lead researcher Dr. Ian Gilron, Director of Clinical Pain Research for Queen’s Departments of Anesthesiology, and Pharmacology & Toxicology, and an anesthesiologist at Kingston General Hospital. “This new treatment approach has the potential to dramatically improve quality of life for people suffering from neuropathic pain, a condition that has puzzled health care workers for years because it is often experienced in areas of the body which appear uninjured.”

Results of the study are published in the March 31 edition of the New England Journal of Medicine.

Also on the team from Queen’s are Joan Bailey (Anesthesiology), Dongsheng Tu (Mathematics and Statistics), Ronald Holden (Psychology,) Robyn Houlden (Medicine); and from Dalhousie University’s Departments of Medicine and Chemistry, Donald Weaver.

“This is exciting news for the health research community in Canada,” says Dr. Rémi Quirion, Scientific Director of CIHR’s Institute of Neurosciences, Mental Health and Addiction. “It is a great achievement for Dr. Gilron and his team, but most importantly, it is a critical research finding for Canadians whose chronic pain may be eased by this research. Dr. Gilron and his team are a shining example of CIHR-funded researchers taking research knowledge from the bench to the bedside.”

Although the research focused on two specific types of neuropathic pain – diabetic neuropathy and postherpetic neuralgia – the methods used in this trial could be employed in studying other chronic conditions such as cancer, spinal disk disease, and the pain experienced after chemotherapy and mastectomies, Dr. Gilron notes. “The numbers of people affected are staggering, and the impact of the problem is devastating and costly.”

Diabetic neuropathy occurs in diabetes patients who experience a constant, burning pain, often in the soles of their feet, that isn’t associated with obvious tissue injury. It is sometimes accompanied by electrical shooting pains up the foot and into the lower leg.

Postherpetic neuralgia results from a re-activation of the virus that causes chicken pox, and usually develops after someone has a herpes zoster or “shingles” infection in an isolated part of the body. In 10 to 20 per cent of people afflicted with herpes zoster, the pain doesn’t go away after the rash disappears. Instead it continues to be felt as a burning sensation and often makes normal touch excruciatingly painful.

Both conditions are due to nerve damage and/or injury, and are associated with the experience of pain in an apparently uninjured area, Dr. Gilron explains. Most of the current treatments for this condition cause side effects, which limit the drug dosage a person can tolerate.

“What we need to do clinically is to achieve a balance between side effects and pain relief,” says the Queen’s anesthesiologist. “The purpose of this study was to evaluate two different drugs for chronic pain, and to carefully measure both the pain-relieving effects and the side effects.”

The clinical trial compared a combination of morphine and gabapentin to each drug alone, as well as to a placebo, in a group of patients with either diabetic neuropathy or postherpetic neuralgia. All the patients received all four treatments.

The results showed that pain intensity was significantly lower with the combination treatment than with either drug alone, or with the placebo. As well, the team found that significantly lower doses of morphine and gabapentin were taken during the combination treatment than during treatment with either drug alone.

“For a lot of these people the pain is unrelenting and it’s unclear when or if it will improve,” says Dr. Gilron. “This new evidence showing that combination treatment provides better pain relief, with comparable side effects, opens the door to exciting possibilities for chronic pain management.”