THE PET PHARMACY By Wendy C. Brooks, DVM, DipABVP Educational Director, VeterinaryPartner.com

(for veterinary information only)

Brand Name: Duragesic Patches

Available in 12.5 microgram per hour, 25 microgram per hour, 50 microgram per hour, 75 microgram per hour, and 100 microgram per hour patches     
 
Uses of this Medication

The primary use of the fentanyl patch is to provide a continuous delivery of pain reliever to a patient with on-going 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 feel pain as well.

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.

The transdermal delivery systems have been popular for continuous delivery of estrogens, nicotine, and anti-nausea medication (scopolamine). It appears that they also provide an excellent means of pain relief delivery.

How this Medication Works

Fentanyl is a narcotic, a member of the same group of drugs as opium and morphine. The following is a simplification of how these drugs affect the body:

Most of us are familiar with at least some of the opiate effects: pain relief, drowsiness, euphoria, addictiveness, diarrhea control, respiratory depression, hallucinations, etc. The opiate drugs bind to different types of opiate receptors throughout the nervous system. Different types of opiate receptors are responsible for creating different narcotic effects. The mu receptor is responsible for the narcotic effects of euphoria, addiction, and respiratory depression. There are also kappa and sigma receptors with other effects. The strength of different opiate drugs is generally compared to those of morphine, which is one of the oldest of the opiates.

Fentanyl binds only the mu receptor and does so approximately 75 to 100 times stronger than morphine. It reaches its peak blood level in 3 to 6 hours in cats but may require a full 12 hours in dogs to reach its full effect. After removal, fentanyl blood levels drop to zero within 24 hours. Patches last at least 4 days in pets.

Side Effects

The most serious potential side effect is respiratory depression (i.e., 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 effect could become a significant risk if the patch is exposed to heating (electric blankets, sitting near a heater vent, heated water bed etc.) The patch may be toxic if swallowed.

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

The euphoria effect can lead to an excessive appetite although in some animals, nausea results from the fentanyl leading to a 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.

There is some variability in the blood levels in different individuals. Some individuals require additional medication for breakthrough pain.

Interactions with other Drugs

Fentanyl should be used with caution in combination with medications that have sedating properties.

Narcotics, including fentanyl, should not be used in patients using L-Deprenylfor either the treatment of Cushing's diseaseor for senility/cognitive dysfunction.

Concerns and Cautions

• Fentanyl is a controlled drug, meaning that specific paperwork is required by certain state and federal government agencies to order it and stock it. Your veterinarian may require you to return any used patches for documentation of proper disposal.

THE APPLICATION OF HEAT TO A FENTANYL PATCH CAN LEAD
TO SUDDEN DELIVERY OF A LARGE AMOUNT OF FENTANYL.

Human deaths have been reported in patients with patches sleeping on heated water beds.
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 small children. Be alert to any children curious about the patch or attempting to manipulate it.

It is our policy not to give dosing information over the Internet.

Date Published: 1/1/2001
Date Reviewed/Revised: 08/21/2008