The role of rapid onset fentanyl products in the management of breakthrough pain in cancer patients.

Breakthrough pain is defined as transient aggravation of pain that arises, despite well controlled or stable baseline pain. It may be preceded by known factors or occur spontaneously. Its prevalence is high and it considerably affects patients' quality of life. Therefore, proper clinical evaluation and treatment is required. Fentanyl transmucosal formulations have become the treatment of choice for spontaneous (idiopathic) episodes because of their rapid onset of action, brief period of analgesia, and easy administration via transmucosal routes. All rapid onset fentanyl formulations show better efficacy than placebo or immediate-release opioids administered via the oral route, with an onset of analgesia within 15 min. Furthermore, most patients show considerable tolerance of these fentanyl formulations, and severe side effects that can potentially be induced by opioids are rarely observed. However, the treatment of breakthrough pain should be adjusted to suit specific patient requirements. Nevertheless, particularly in predictable bursts of pain and also in spontaneous episodes of breakthrough pain with slowly intensifying pain, immediate-release formulations of opioids may play an important role.