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Fentanyl – Strongest Analgesic Drug for Chronic Pain

Fentanyl is a drug with a strong analgesic power normally used by transdermal patches for the treatment of chronic pain.

Fentanyl is an analgesic drug derived from morphine that is indicated to alleviate chronic pain, in patients with cancer, in neuropathies and in many other diseases.

It is a drug that has a high affinity for morphine receptors, whose activation induces a high intensity analgesia , much higher than the analgesic power of NSAID drugs, such as ibuprofen . Let’s look at the following points of fentanyl:

  • General characteristics.
  • Mechanism of action.
  • Pharmacokinetics
  • Adverse reactions.

General characteristics

This drug is a pure agonist of morphine receptors . It interacts fundamentally with the μ receptors presenting maximum intrinsic activity.

It is a drug whose pharmaceutical form of administration is mainly transdermal patches. This results in a continuous release of fentanyl for 72 h . As stated at the beginning of the article, it is a drug indicated for patients suffering from chronic pain.

However, being constantly under the effects of this analgesic, there are people who can develop tolerance to its effects. This degree of tolerance will vary from one individual to another .

On the other hand, its administration is completely contraindicated in patients who are allergic to morphine , those who have respiratory depression (if uncontrolled it can produce death) and in patients with COPD.

Mechanism of action

Fentanyl, as we already know, binds selectively to μ morphine receptors. This receptor, like the other types of morphine receptors, is coupled to G proteins. By binding, it blocks the action of the adenylate cyclase enzyme and as a result, cAMP levels decrease.

Adenylate cyclase is an enzyme that is part of the signaling cascade of the G protein . When the signal reaches the receptor, which is coupled to this protein, the message is transmitted, thanks to the G protein, to the adenylate cyclase to enter it inside the cell and trigger the corresponding action.

Chlorine channels and benzodiazepines

In this case, the objective is to block the potassium channels (K) of the cell membrane, preventing the pain signal from being transmitted.


Fentanyl can be sold parenterally, transmucosally and transdermally , the latter being the most used. When applied by this route, the drug presents a good absorption, reaching its maximum concentration in blood at 12-24 hours.

It binds in a high proportion to plasma proteins , approximately 80-85%. This characteristic is important, because if it is administered together with another drug that also binds these proteins in a high proportion, they can move between them. If this interaction occurs, the levels of fentanyl in the blood can increase considerably, producing undesirable effects or even producing a toxicity picture.

As for your metabolism, it does not seem to be metabolized in the skin, since 92% of a transdermal dose can be found without changes in the blood. However, it is metabolized in the liver through oxidation reactions. Its metabolites and the rest of the unchanged drug are eliminated by urine.

Side Effects

The treatment with fentanyl can develop undesirable effects for the organism, being the most significant the respiratory depression . However, it can also produce others quite frequently (10-25% have been observed) as:

  • Nausea and vomiting.
  • Constipation.
  • Drowsiness.
  • Euphoria and sweating.

On the other hand, there are also a series of symptoms that may appear but less frequently . They have been observed in 1-9% of patients treated with fentanyl. These are, for example, convulsive symptoms, urinary retention, hypertension, muscle rigidity or alterations in mood.

Addiction and dependence

Keep in mind that both fentanyl and other drugs derived from morphine, have addictive effects. Addiction is the compulsive desire to get the drug or the drug . This effect appears easily in recreational use and does not appear frequently in patients who use it as a treatment.

However, tolerance and physical dependence are two very frequent effects of the use of fentanyl as a drug when it comes to relieving pain.

Unbridled adolescence and drugs

The pharmacological tolerance is the need to increase the doses of the drug to maintain the pain relief that it produced at the beginning of the treatment. It is presented as a decrease in the duration of analgesia and is treated by increasing the dose of the drug.

As for dependency, we must distinguish between physiological and psychological dependence. The first is due to a sudden suppression of fentanyl administration after chronic use. When this happens, a series of symptoms that constitute the withdrawal syndrome are triggered .

Psychological dependence is a behavioral syndrome characterized by the desire of the corresponding dose as well as avoiding the resulting discomfort not being able to consume it.

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