Pharmacological approaches other than opioids in chronic non-cancer pain management

Abstract

Many pains are controlled by non-addictive procedures ranging from exercise to a variety of analgesic medications. Some pains are controlled by analgesic drugs, but at the cost of intolerable side effects. This is true both for non-steroidal anti-inflammatory drugs and opioids. The worst pains are most often controlled by opioids, but problems of tolerance and addiction limit these successes. This contribution provides a statement on non-addictive, non-opioid drugs which help to control pain. Just as these vary in their success, so they vary also in the strength of the scientific evidence which supports their use. The groups of drugs to be considered can be evaluated in three respects; evidence of analgesic effect in controlled trials; evidence of side-effects compared with control substances and with standard experience; evidence of usefulness in clinical practice. The latter which is the most important for practice often has the least scientific proof. Six main classes of drugs are recognized which provide analgesic effects, other than opioids. 1) Non-steroidal anti-inflammatory drugs are widely accepted as analgesics on the basis of animal studies, numerous controlled investigations and clinical practice. Acetaminophene may not be anti-inflammatory, but is recognized as an effective analgesic which in many other respects resembles the above. 2) Muscle relaxants, e.g. cyclobenzaprine or baclofen have varied actions, but often provide some relief of pain. 3) Antidepressants may be analgesic if they relieve depression which is giving rise to pain. This applies to all anti-depressants. Some antidepressants have been shown to be analgesic in the absence of depression. The best accredited of these is amitriptyline. Antidepressants too have significant side effects. A serotoninergic hypothesis is insufficient to explain the actions of antidepressants in relieving pain in the absence of depression. 4) Phenothiazine neuroleptics (and possibly some others) may be analgesic. Drugs reported to be analgesic include chlorpromazine, fluphenazine, perphenazine, trifluoperazine, methotrimeprazine (levomepromazine) among others. Haloperidol has also been utilized. Well controlled evidence exists with the use of methotrimeprazine (levomepromazine) used as an injection. The analgesic effect of oral neuroleptics is less well established and mostly depends upon clinical observation, withdrawal and re-challenge. 5) Anticonvulsants. 6) Other drugs. Non-steroidal anti-inflammatory drugs and some muscle relaxants, e.g. cyclobenzaprine are best used in the short term. The gastrointestinal side effects of non-steroidal anti-inflammatory drugs have been quite troublesome and over 2% of patients followed over five years are at risk of developing peptic ulceration from such medication. Cyclobenzaprine is best used in short term treatment, but may be used intermittently for chronic pain. Antidepressants, neuroleptics, anticonvulsants and some other drugs can be used long term. Topical analgesic agents may also be used.