[The pharmacologic basis of pain treatment]

The treatment of chronic pain uses drugs from different pharmacological classes. Analgesics are the common basis of these treatments. Peripheral analgesics (or minor analgesics such as paracetamol) and non-steroidal anti-inflammatory drugs are used for moderate pain (grade I of WHO). Major analgesics, opioids, are used for more severe pain (grades II and III). When pain can be related to a precise cause or location, more specific drugs may be used. This is done in migraine, facial pain, muscular spasms, dental pain, local inflammation. Chronic pain of grades II and III is treated with opioids. According to the severity, agents of different powers are used: partial agonists, full agonists of receptors OP3 (mu) and OP2 (kappa). According to other pathological signs linked to pain, coanalgesic drugs may be used in association: psychotropic drugs, either psycholeptic drugs which act synergistically with analgesics and bring their own effects, anxiolytic and/or neuroleptic, or anti-depressants which inhibit the depression state that may be associated with pain. Corticosteroids are also very useful for the numerous effects they induce: inhibition of the inflammation process, CNS stimulation, analgesics in medullary, or plexus compressions and in elevations of intracranial hypertension. Moreover their metabolic effects may be useful in cachectic states. The pharmacological treatment of chronic pain of grades II and III poses the problem of chronic administration of increasing doses of opioids and of their coprescription, of acquired tolerance, of dependence and of toxicity induced by drug accumulation.