Stimulation of alpha;2-adrenoceptors in different regions of the brain and the spinal cord mediates antinociception. Animal studies as well as studies in patients give evidence that the alpha;2-adrenoceptor agonist clonidine is a helpful adjunct in the therapy of chronic pain syndromes. In sympathetically maintained pain topically applied clonidine has shown to be effective as the sole treatment. In cancer patients the concommittant use of clonidine may help to reduce opioid requirements and side effects of high-dose opioid administration. Some patients suffering from neuropathic pain sydromes respond well to the administration of clonidine. In general, the epidural or intrathecal route is more effective than intravenous or oral administration. Independent of the route of administration, a dose of 300 micro;g clonidine is usually adequate but much lower doses have been shown to be effective. Side effects such as bradycardia and hypotension do not limit the usefulness of clonidine but require careful monitoring when therapy is initiated.
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