Monday, June 5, 2023
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Fentanyl was first synthesized in 1960 and found to be significantly more potent than commonly used opioids, such as morphine or meperidine. At the time, researchers were looking for more potent opioids because potency seemed to be directly related to safety. More potent drugs were believed to be safer because it was thought that at equianalgesic doses there would be fewer unbound molecules to affect sites not related to analgesia but responsible for respiratory depression and other side effects.
Consistent with this concept, in animal studies, fentanyl had a much larger safety margin when compared with older opioids. The large safety margin, relatively short duration of action, and minimal respiratory depression at analgesic doses observed for fentanyl soon made it the drug of choice for intravenous anesthesia.[1] Its ability to provide cardiovascular stability and to block the stress response to surgical stimuli at high doses made it the mainstay of cardiac anesthesia. However, when used at high doses to suppress the stress response during surgery, significant respiratory depression results and postoperative mechanical ventilation are usually needed.[2]
Although fentanyl is still used extensively in the perioperative period, the clinical features that have made fentanyl so successful in this setting have also made this drug a uniquely useful tool in the management of chronic pain. For this reason, fentanyl has moved out of the operating room and into the clinic.
This column focuses on why lipid solubility makes fentanyl uniquely useful in treating persistent chronic pain (basal pain) and sudden flares of breakthrough pain (BTP). BTP, which is also called "incident pain" or "episodic pain," is defined as a transitory exacerbation of pain that occurs on a background of otherwise controlled chronic pain.[3-5]
