Rapid onset opioids in palliative medicine.

Opioids are potent broad-spectrum analgesics useful to treat a variety of painful conditions. Opioids have been classified by many different categorizations (e.g. natural, semisynthetic, synthetic). One classification that may be useful in terms of selecting specific opioid agents is based on the pharmacokinetic characteristics of the various opioid formulations (e.g. longacting opioids, short-acting opioids, and rapid onset opioids). These various opioid agents appear to be useful to "match" specific types of pains. Rapid onset opioids appear especially well-suited to treat breakthrough pain and in particular, rapidonset breakthrough pain. This article will briefly review 5 rapid onset opioids that are FDA approved in the U.S.