Opioids for persistent non-cancer pain

Epidemiological studies from Australia and Denmark indicate that about 19% of the population is afflicted by chronic pain that is not caused by cancer.¹,² The prevalence of chronic pain that interferes with daily activities is 12.6%.¹ In most Western countries, opioids are established in treating pain due to cancer, and they are increasingly used to manage chronic pain not due to cancer. Opioids are effective analgesics, but they also have a strong reinforcing potential—fear of addiction and diversion restrict their medicinal use. Good clinical trials, guidelines, and responsible prescription are needed to ensure the availability of opioids for those patients who may benefit.³,⁴

A recent systematic review included 11 randomised and controlled trials on oral opioids in non-cancer pain.⁵ The review showed that opioids provided pain relief for both neuropathic (postherpetic neuralgia, diabetic neuropathy) and musculoskeletal pain (osteoarthritis). Large differences between individuals in the response to opioids in all conditions implied that the effectiveness of the treatment should be tested in each individual. Adverse effects were common and included constipation, nausea, vomiting, somnolence, sedation, dizziness, itching, dry mouth, and headache. The studies were of short duration (four days to eight weeks in each treatment arm). Some studies included an open label phase for up to two years, but only a few patients continued to use opioids.

When treating pain due to cancer, alleviating symptoms is the main goal, whereas in the management of chronic non-cancer pain the goal is to keep the patient functional, both physically and mentally, with improved quality of life. Relief of pain may be an essential factor in this and opioids are only one aspect of the overall rehabilitative strategy for the patient. In a few instances, such as when an elderly patient is waiting for a hip replacement, opioids can be regarded as a fairly straightforward means of alleviating pain for a limited period. The more chronic and complex the problem and the younger the patient, the lesser is the role opioids have in the rehabilitation plan. A multidisciplinary pain clinic will try other analgesics (including antidepressants and anticonvulsants), non-steroidal anti-inflammatory drugs, weak analgesics, transcutaneous nerve stimulation, cognitive behaviour therapy, and exercise programmes.

Opioids are not effective in every patient with pain. Randomised controlled trials indicate that no criteria have been identified that predict good response to opioids in any particular condition. Also, these trials were of short duration and included a selected group of patients. Many questions regarding safety, such as long term effects on hormonal and immune function, development of tolerance and increased pain sensitivity, addiction and diversion of drugs were not answered by these trials.⁶ Therefore, each patient who is considered for treatment with opioids needs to be assessed for both efficacy and safety. Good monitoring serves the individual patient and provides valuable information from areas that cannot be studied in randomised and placebo controlled studies, such as tolerance, addiction, and diversion of drugs.

Patients need to be informed of the possible benefits and risks of opioid treatment, and they need to be monitored carefully. This takes time. Treatment of young patients and patients with psychosocial problems or addictive behaviour should be initiated in multidisciplinary pain clinics that have the resources and expertise to assess these problems. However, primary care doctors should always be involved in the decision making as they will usually take responsibility for the patients in the long term. Multidisciplinary pain clinics should be available for consultation if problems occur. These clinics should also follow and audit to ensure that information gained over the years is used to reassess the appropriateness of the treatment.

Opinions regarding the medicinal use of opioids have always been polarised. History shows how too liberal use has led to heightened regulatory control, reluctance of doctors to prescribe opioids, and under-treatment of pain. Guidelines are needed to prevent history repeating itself. The British Pain Society published its recommendations for the appropriate use of opioids for persistent non-cancer pain in March 2004.⁴ The document includes information for the patient, who is an important partner in the treatment plan. The recommendations were carefully worked out with consultations of the royal colleges of anaesthetists, general practitioners, and psychiatrists. They are based on what is known about the effectiveness of opioids in the treatment of chronic non-cancer pain. The recommendations acknowledge the lack of data in many important areas of clinical research; in these areas they are based on clinical experience. The recommendations provide an excellent balanced framework. Individual pain specialists and primary care doctors now need to work within this framework and collect data through good monitoring. Such data will be valuable when the recommendations are reviewed in March 2007.