Breakthrough pain in cancer patients: characteristics, prevalence, and treatment.

"Breakthrough pain" is a common clinical term that has not been conclusively defined or described. Breakthrough pain is a transitory flare of pain experienced when baseline pain has been reduced to a mild or moderate level. Breakthrough pain may be characterized by its relationship to a fixed around-the-clock (ATC) opioid dose, rapid onset and short duration, precipitating events, predictability, pathophysiology (with nociceptive pain being most easily controlled), and etiology. The only prospective study of breakthrough pain conducted to date found a 63% prevalence of breakthrough pain in cancer patients referred to a pain service. Although prevalence figures from other studies vary widely, partly due to the populations chosen, all of the studies verify that breakthrough pain is a serious problem in cancer patients. In fact, several studies have listed incident pain, a subset of breakthrough pain, as a predictor of poor response to analgesic therapy. Breakthrough pain is currently managed with oral or parenteral breakthrough pain medications given in addition to the ATC analgesic regimen. The ATC dosage may also be increased until limited by side effects. Newer agents with a more rapid onset of analgesia and shorter duration of effect may help in the management of breakthrough pain.