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Fentanyl is approximately 100 times more potent than morphine, with 100 micrograms of fentanyl approximately equivalent to 10 mg of morphine and 75 mg of pethidine (meperidine) in analgesic activity. It has an of 3.1 milligrams per kilogram in rats, and an LD50 of 0.03 milligrams per kilogram in monkeys. Fentanyl was first synthesized by Dr. Paul Janssen in 1960 following the medical inception of pethidine several years earlier. Janssen developed fentanyl by assaying analogues of the structurally-related drug pethidine for opioid activity. The widespread use of fentanyl triggered the production of fentanyl citrate (the salt formed by combining fentanyl and citric acid in a 1:1 stoichiometry), which entered the clinical practice as a general anaesthetic under the trade name Sublimaze in the 1960s. Following this, many other fentanyl analogues were developed and introduced into the medical practice, including sufentanil, alfentanil, remifentanil, and lofentanil. In the mid 1990s, fentanyl saw its first widespread palliative use with the clinical introduction of the Duragesic patch, followed in the next decade by the introduction of the first quick-acting prescription formations of fentanyl for personal use, the Actiq lollipop and Fentora buccal tablets. Through the delivery method of transdermal patches, fentanyl is currently the most widely used synthetic opioid in clinical practice, with several new delivery methods currently in development. |