Fentanyl

Fentanyl is a pain medication and is one of the highly potent opioids. The analgesic potency is about 100 times that of morphine. It is used in particular in anesthesia for general anesthesia and in emergency medicine for very severe pain, for example in traffic accidents, bone fractures or burns. For severe chronic pain, it can be used as a transdermal patch on the skin.

PharmacodynamicsThe drug acts agonistically at µ-opioid receptors, thereby relieving pain and sedating. Additional effects include respiratory depression, reduction of coughing stimulus, reduction of pulse and blood pressure, and euphoria.

PharmacokineticsThe effective analgesic dose is 0.002 to 0.02 mg per kilogram of body weight, about 120 times higher than moprhine. The analgesic is lipophilic and is excreted mainly by the liver, with less than ten percent excreted by the kidneys. The duration of action depends to a large extent on the method of administration; after intravenous injection, the effect is rapid and lasts for about 30 minutes. In the case of sublingual tablets, the analgesic effect lasts four to six hours, and with transdermal application even 48 to 72 hours.

InteractionsWeaker opioids bind to the same receptors and can block them, so that the effect of fentanyl is weakened. Degradation occurs via CYP3A4, so inducers of this enzyme (e.g., rifampicin, St. John's wort) may decrease the effect of fentanyl, and inhibitors (e.g., clarithromycin, ketoconazole) may increase side effects. When used together with monoamine oxidase inhibitors, the circulatory and respiratory depressive effects may be increased. Also, caution is advised when combined with serotonergic antidepressants (SSRI/SNRI), as this may lead to serotonin syndrome with blood pressure crises, hallucinations, and coma.

Sideeffects Common side effects include a decrease in respiratory drive, which is why continuous monitoring and ventilation should be provided, especially with intravenous administration. Furthermore, constipation, urinary retention, bronchospasm, and acute cardiac failure may occur.

Toxicological dataIn monkey experiments, the lethal dose was as low as 0.03 mg per kilogram of body weight. For a normal-weight adult, as little as 2 mg may be lethal.