Fentanyl, Sufentanil, and Alfentanil
Fentanyl (Sublimaze) and its related phenylpiperidine derivatives are extremely potent drugs. They are used as adjuncts to anesthesia, and fentanyl may be given trans-dermally as an analgesic and as an oral lozenge for the induction of anesthesia, especially in children who may become anxious if given IV anesthesia.
Fentanyl is 80 to 100 times as potent as morphine. Sufentanil (Sufenta) is 500- to 1,000-fold more potent than morphine, while alfentanil (Alfenta) is approxi-mately 20 times more potent than morphine. Their on-set of action is usually less than 20 minutes after admin-istration. Dosage is determined by the lean body mass of the patient, since the drugs are lipophilic and tend to get trapped in body fat, which acts as a reservoir, pro-longing their half-life. In addition, redistribution of the drugs from the brain to fat stores leads to a rapid offset of action. Droperidol, a neuroleptic agent, is generally administered in combination with fentanyl for IV anes-thesia.
Fentanyl transdermal patches are available for anal-gesia in chronic pain and for postsurgical patients. The use of the patch is contraindicated, however, for pa-tients immediately after surgery because of the pro-found respiratory depression associated with its use. The patches must be removed and replaced every 3 days. The onset of action of transdermal fentanyl is slower than that of oral morphine. Thus, patients may require the use of oral analgesics until therapeutic lev-els of fentanyl are achieved. Fentanyl lozenges have been used to induce anesthesia in children and to re-duce pain associated with diagnostic tests or cancer in adult patients. However, all of the adverse side effects associated with morphine are produced with far greater intensity, but shorter duration, by fentanyl in the patch, the lozenge, or IV administration. Given the abuse lia-bility of fentanyl, controversy exists as to the ethics of marketing a lollipop lozenge form.
Sufentanil is much more potent than fentanyl and is indicated specifically for long neurosurgical procedures. In such patients, sufentanil maintains anesthesia over a long period when myocardial and cerebral oxygen bal-ance are critical.
Fentanyl is commonly used to relieve pain from in-tubation of premature infants, although the safety of thedrug in infants has not been established. Sufentanil has been studied to a limited extent in newborns, and re-ports indicate that it can be used safely. Tolerance and physical dependence have been demonstrated after prolonged use of fentanyl in the newborn.
In addition to all of the adverse effects and contraindi-cations previously described for morphine, the follow-ing contraindications apply specifically to these drugs. They are contraindicated in pregnant women because of their potential teratogenic effects. They also can cause respiratory depression in the mother, which re-duces oxygenation of fetal blood, and in the newborn; the incidence of sudden infant death syndrome (SIDS) in the newborn is also increased.
Cardiac patients need to be monitored closely when receiving these drugs because of their bradycardiac ef-fects (which can lead to ectopic arrhythmias), and hy-potensive effects resulting from prolonged vasodilation. In addition, the drugs stiffen the chest wall musculature, an effect reversed by naloxone.