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Fentanyl is a narcotic; a member of the same group of drugs as opium and morphine. Most of us are familiar with at least some of the opiate effects: pain relief, drowsiness, euphoria, addictiveness, diarrhea, respiratory depression, and hallucinations. The opiate drugs bind to different types of opiate receptors throughout the nervous system. Fentanyl is approximately 75-100 times stronger than morphine. It reaches its peak blood level in 3-6 hours in cats but may take a full 12 hours in dogs. Signs such as addictiveness and hallucinations are felt not to be observed in pets, with the use of Fentanyl.

The primary use of the Fentanyl patch is to provide a continuous delivery of pain reliever to the patient with ongoing pain. These patches are especially useful after a surgical procedure but are also helpful after injury or in the management of cancer-related pain, particularly if giving pills is problematic. In the past, pain relievers have been given as shots or pills on an as-needed basis. Since it is difficult to determine when an animal is in pain, the basic guideline is to consider the pain that human patients report after similar surgeries or injuries. If a human would be expected to experience pain in a similar circumstance, then it can be assumed that an animal would be expected to feel pain as well. Some individuals require additional medication for breakthrough pain.

Side Effects

The most serious potential side effect is respiratory depression (not breathing adequately). This is a rare problem but if unusual weakness or drowsiness is observed, the patch may be creating a stronger effect than expected. The patch may be removed if there is any concern. This could become a significant risk is the patch is exposed to heat.

The patch may be toxic is swallowed.

Occasionally, a pet reacts to the adhesive on the back of the patch. Such skin reactions should resolve with patch removal.

The euphoria effect can lead to an excessive appetite although in some animals. Nausea may also result from Fentanyl, leading to reduced appetite.

Fentanyl is not felt to be a sedative in cats but in dogs some sedation may be observed. A wobbly gait may be a sign of sedation.

Interactions with other Drugs

Fentanyl should be used with caution in combination with medication that has sedating properties.

Cautions and Concerns

Fentanyl is controlled drug, meaning that specific paperwork is required to order it and stock it.

If your pet has a Fentanyl patch, be sure to avoid situations where the patch could be excessively heated.

Fentanyl patches may be toxic if swallowed by children or pets.

Veterinarian’s Comment

If a Fentanyl patch is applied to your pet’s skin, it should be removed as advised by your veterinarian in order to prevent an over-dosage. A glove should be worn when removing the patch and should be discarded appropriately (not in household garbage).

Research into the human experience of pain and its relief has yielded some important information.

  • Recovery from illness is faster if pain is alleviated.
  • It is more effective to prevent pain than to alleviate existing pain (i.e., using pain medications in anticipation of pain is more effective than waiting until the pain already exists).
  • Continuous delivery of pain relief is more effective than periodic administration of pain relief.


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