How fentanyl works
Fentanyl is a strong analgesic from the group of opioids. Its analgesic potency is about 125 times that of morphine.
The nerves in the body conduct stimuli, including pain stimuli, from almost every part of the body to the central nervous system (= brain and spinal cord). The intensity of the stimulus depends on the trigger and the level of endorphins. These are natural hormones that reduce the perception of pain. When the endorphin level in the body is high, pain is perceived less strongly. The same effect, i.e. reduced pain perception, can be achieved with opiates and opioids.
Opiates are naturally occurring substances in the poppy plant that inhibit the sensation of pain. Opioids are chemically synthesized substances modeled on opiates that have the same analgesic mechanism of action as opiates.
Onset of action depends on dosage form
Because fentanyl has a strong analgesic effect, only very small amounts of it are needed to effectively suppress pain. This allows for a variety of dosage forms, all of which deliver the active ingredient to the body at different rates.
Fentanyl injections (syringes) are the fastest-acting. These are followed by forms of administration in which the active ingredient is absorbed through the oral or nasal mucosa, such as lozenges and nasal spray (onset of action within minutes).
If fentanyl is applied to the skin in the form of a patch, the onset of action is slowest (only after several hours).
Absorption, breakdown and excretion
The amount of fentanyl that enters the body depends – similar to the onset of action – on the form of administration (lozenge, nasal spray, patch, etc.). For example, only 5 percent of the applied active ingredient is absorbed via the oral mucosa, compared with around 70 percent when taken orally.
In the case of slow-release dosage forms (sustained-release preparations) and patches containing fentanyl, this period is correspondingly longer; in the case of infusions or injections, it is comparatively shorter.
When is fentanyl used?
Fast-acting dosage forms (such as fentanyl nasal spray, lozenge/sucker, or injections) are used to treat severe and intense pain, such as that experienced in tumor diseases or intensive care patients (breakthrough pain).
In addition, fentanyl is used before operations for anesthesia in combination with other active ingredients. In such cases, it is only used for a short time.
Slow-release dosage forms such as fentanyl patches are used to treat chronic severe pain that can only be adequately treated with opioid painkillers. The use here usually extends over a longer period of time.
How fentanyl is used
When treating chronic pain with a fentanyl patch, the selected skin area (unshaven, uninjured) is cleaned with clean water and dried well before application. Any hair can be carefully cut off with scissors.
After that, remove the protective foil from the patch and stick the patch on the desired skin area (press lightly for 30 seconds). It then releases the painkiller constantly for usually three days. After that, if necessary, a new patch should be applied to a different area of the skin.
When pulling off the old plaster, care must be taken to ensure that no remnants of the plaster remain stuck to the skin. A fentanyl patch can be reapplied to the affected skin site after one week at the earliest.
After removal, the patch is disposed of properly (as explained by the doctor or pharmacist). Since even used patches still contain active substance, this step is important to ensure that no uninvolved persons come into contact with it (e.g. small children).
What are the side effects of fentanyl?
The side effects are strongly related to the mode of action of the substance and are therefore also dose-dependent. At low doses, there are often no or only minor side effects. As the dose increases, they become more pronounced.
In more than one in ten patients, fentanyl causes drowsiness, dizziness, dizziness, pupil constriction, a slowed heartbeat, a drop in blood pressure, nausea and vomiting. These adverse effects are especially likely to occur at the beginning of therapy.
In addition, side effects such as sweating, rash, itching, central dullness, confusion, visual disturbances, cardiac arrhythmias, respiratory reflex depression, digestive disturbances (such as constipation), and urinary retention occur in one in ten to one in one hundred people treated.
In addition, side effects such as skin reactions at the adhesive site of the patch are possible with the fentanyl patch.
What should I be aware of when using fentanyl?
Interactions
Note that alcohol in combination with fentanyl can significantly impair the ability to react in road traffic.
It is also not advisable to take medications that affect the level of the nerve messenger serotonin at the same time. These include antidepressants (MAO inhibitors, SSRIs), migraine medications such as sumatriptan, and serotonin precursors such as tryptophan. Simultaneous use of such agents and fentanyl can lead to a so-called serotonin syndrome (rapid pulse, sweating, hallucinations, convulsions, etc.).
Fentanyl is metabolized in the liver via the so-called cytochrome P450 3A4 enzyme (CYP3A4). When using other drugs that are broken down by the same enzyme, it may be necessary for the treating physician to increase or decrease the fentanyl dosage.
For example, a dose increase may be necessary with certain anticonvulsant drugs (carbamazepine, phenytoin, valproate). Ritonavir (HIV medication) and clonidine (for example, for high blood pressure and heart palpitations), on the other hand, may make it necessary to reduce the fentanyl dose.
Age restriction
Fentanyl for intravenous use is approved for patients as young as one year of age. Patches containing fentanyl may be used in patients two years of age and older.
Lozenges and lozenges with an applicator for use in the oral cavity (fentanyl stick) are not approved until patients are 16 years of age or older, while buccal tablets (for insertion into the cheek, where the active ingredient is absorbed through the mucous membrane) and nasal spray are approved from 18 years of age.
In elderly patients and patients with liver or kidney disease, the breakdown and excretion of fentanyl may be slowed. Therefore, dosage often needs to be reduced in these cases.
Pregnancy and lactation
Fentanyl should not be used during pregnancy due to a lack of data, as it crosses the placenta. To date, however, there is no evidence of any adverse effect on fertility.
Therefore, if indicated, fentanyl may be used throughout pregnancy. If fentanyl is administered shortly before delivery, side effects such as respiratory depression and adaptation disorders in the infant are possible.
How to obtain medication with fentanyl
Fentanyl is available on prescription in Germany, Austria and Switzerland in any dosage and dosage form. It is also considered a narcotic and is subject to the Narcotics Act (Germany and Switzerland) or the Narcotic Substances Act (Austria).
The doctor must therefore prescribe it on a special prescription. Anyone wishing to carry fentanyl on trips (especially those abroad) should first obtain a certificate from a doctor confirming legal possession of the narcotic.
How long has fentanyl been known?
Fentanyl was developed by Paul Janssen in 1959 and commercialized in the 1960s. In the mid-1990s, a newly developed pain patch (fentanyl is otherwise very short-acting) came on the market for the treatment of chronic pain.
Later, fentanyl sticks (“lollipops”), buccal tablets and a mouth and nasal spray containing fentanyl were also developed.
