(for veterinary information only)
12.5 microgram per hour,
25 microgram per hour,
50 microgram per hour,
75 microgram per hour,
and 100 microgram per hour
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.
Animals need pain relievers in the same situations that humans do.
Clearly it behooves us to relieve animal pain and this must be done effectively and without getting bitten by the patient we are trying to help. Transdermal drug delivery (through patches applied to the skin) has been very popular for a number of human medications. It turns out many of these can be adapted to pets. This allows not only for continuous pain relief delivery but also allows for medication to be administered without manipulating the patient's mouth.
Fentanyl is a narcotic, a member of the same group of drugs to which opium and morphine belong.
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, strong pain relief, addiction, and respiratory depression. There are also “kappa,” "delta," and “sigma” receptors with other effects such as pupil constriction and hallucinations. In seeking to relieve pain, we want to select a strong mu receptor stimulant without stimulating the other receptors.
Fentanyl binds only the mu receptor and does so approximately 75 to 100 times stronger than morphine, making it an excellent choice for pain relief. 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.
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 application of a topical cortisone product.
The euphoria effect can lead to an excessive appetite though 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 achieved by different individuals. Some individuals require additional medication for breakthrough pain.
Fentanyl should be used with caution in combination with medications that have sedating properties such as antihistamines or other sedating pain relievers. Over-sedation may result.
Narcotics, including fentanyl, should not be used in patients using Anipryl/L-Deprenyl for either the treatment of Cushing's disease or for senility/cognitive dysfunction.
- Fentanyl is a controlled drug, meaning that specific government paperwork is required 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 conscious of any children curious about the patch or attempting to manipulate it.
Page last updated: 11/5/2013