The Metabolites of Fentanyl and its Derivatives

Since its introduction in the 1960s, fentanyl has found widespread clinical use as a morphinomimetic narcotic analgesic, primarily in the form of its citrate salt Sublimaze, Fentanest, Pentanyl. With a potency in rats of almost three hundred times that of morphine, its onset time and duration of action are considerably shorter than that of the naturally occurring opiate. Its safety margin is well over 100 in animal studies. In man, its activity is somewhat attenuated, for example, intramuscular administration of fentanyl in clinical studies has led to potency ratio estimates of 50. These properties have occasioned its popularity in surgical analgesia, especially when combined with a powerful tranquilizer such as droperidol in the technique of neuroleptanalgesia. An extensive literature search identified 15 metabolites for the synthetic opiod fentanyl. Sufentanil and alfentanil had 2 and 3 reported metabolites respectively. Factors determining the metabolic fate of these opiods, as well as the nature and quantity of metabolites isolated, are discussed. Keywords Opium alkaloids.