What is Fentanyl?
Fentanyl, also spelled fentanil, is an opioid used as a pain medication and together with other medications for anesthesia. Fentanyl is also used as a recreational drug, often mixed with heroin or cocaine. It has a rapid onset and its effects generally last less than two hours. Medically, fentanyl is used by injection, nasal spray, skin patch, or absorbed through the cheek (transmucosal) as a lozenge or tablet.
Common side effects include vomiting, constipation, sedation, confusion, hallucinations, and injuries related to poor coordination. Serious side effects may include decreased breathing (respiratory depression), serotonin syndrome, low blood pressure, addiction, or coma. Fentanyl works primarily by activating μ-opioid receptors. It is around 100 times stronger than morphine, and some analogues such as carfentanil are around 10,000 times stronger.
Intravenous fentanyl is often used for anesthesia and to treat pain. To induce anesthesia, it is given with a sedative-hypnotic, like propofol or thiopental, and a muscle relaxant. To maintain anesthesia, inhaled anesthetics and additional fentanyl may be used. These are often given in 15–30 minute intervals throughout procedures such as endoscopy, surgeries, and in emergency rooms.
For pain relief after surgery, use can decrease the amount of inhalational anesthetic needed for emergence from anesthesia. Balancing this medication and titrating the drug based on expected stimuli and the person’s responses can result in a stable blood pressure and heart rate throughout a procedure and a faster emergence from anesthesia with minimal pain.
Fentanyl is sometimes given intrathecally as part of spinal anesthesia or epidurally for epidural anaesthesia and analgesia. Because of fentanyl’s high lipid solubility, its effects are more localized than morphine, and some clinicians prefer to use morphine to get a wider spread of analgesia. However, it is widely used in obstetrical anesthesia because of its short time to action peak (about 5 min), the rapid termination of its effect after a single dose, and the occurrence of relative cardiovascular stability. In obstetrics, the dose must be closely regulated in order to prevent large amounts of transfer from mother to fetus. At high doses, the drug may act on the fetus to cause postnatal respiratory distress. For this reason, shorter acting agents such as alfentanyl or remifentanil may be more suitable in the context of inducing general anaesthesia.
It is also used in the management of chronic pain including cancer pain. Often, transdermal patches are used. The patches work by slowly releasing fentanyl through the skin into the bloodstream over 48 to 72 hours, allowing for long-lasting pain management. Dosage is based on the size of the patch, since, in general, the transdermal absorption rate is constant at a constant skin temperature. Rate of absorption is dependent on a number of factors. Body temperature, skin type, amount of body fat, and placement of the patch can have major effects. The different delivery systems used by different makers will also affect individual rates of absorption. Under normal circumstances, the patch will reach its full effect within 12 to 24 hours; thus, fentanyl patches are often prescribed with a fast-acting opioid (such as morphine or oxycodone) to handle breakthrough pain. It is unclear if fentanyl gives long-term pain relief to people with neuropathic pain.