Introduction

A rapidly evolving understanding of the neurobiology of pain has:

• Allowed development of novel compounds likely to modify the pain experience.

• Provided a scientific rationale for the use of a number of classes of existing drugs in the treatment of pain.

Similarly, empirical observations regarding the efficacy of such drugs have illuminated some of the mechanisms involved in pain processing.

Pains associated with nervous system damage or dysfunction (neuropathic and central pain syndromes) are often refractory to conventional analgesic therapy. It is in this spectrum of disorders that (inappropriately so called) ‘non-analgesic’ drugs are most frequently used. The drugs used are chemically diverse compounds and many have a number of relevant actions in the treatment of pain. It is important to note that the published data on these drugs relate to their use in relatively few, specifically defined, pain conditions. In contrast, many patients present a mechanistically more complex picture. The use of these drugs in the more general pain population is, therefore, based on inferences drawn from specific studies augmented by clinical experience.

Antidepressant drugs

History

Tricyclic antidepressants were first synthesised in the 1940s and used for the treatment of depression a decade later. The drugs were subsequently shown to have analgesic properties both in patients with chronic pain-induced depression, and also in those with normal mood.