[Treatment of cancer pain: the role of co-analgesics].

Opioid analgesics are widely acknowledged as the most important drugs for the treatment of chronic cancer pain. Although these drugs can in most cases control severe pain, even when they are used appropriately, they may produce new symptoms or exacerbate preexisting symptoms, most notably nausea and somnolence. The combination of severe pain, anorexia, chronic nausea, asthenia, and somnolence is a frequent finding in patient with advanced cancer. An adjuvant drug should meet at least one of the following criteria: 1) to increase the analgesic effect of opioids; 2) to decrease their toxicity; 3) to improve others symptoms associated with terminal cancer. Many drugs, such as nonsteroidal antiinflammatory agents, tricyclic antidepressants, corticosteroids, benzodiazepines, amphetamines, antiemetics, oral local anesthetics and bisphosphonates have been suggested to have adjuvant analgesic effects. Unfortunately, most of the evidence for the effects of these drugs is anedoctal. Controlled clinical trials are badly needed to precise the indications and the risk/benefit ratios of these agents, some of which have significant toxicity and could potentially aggravate narcotics toxicity.