Moderate and Severe Pain
Moderate pain can be treated with one of the NSAIDs; however, these frequently fail to meet the needs of the patient. Opiates such as fentanyl are often used to relieve moderate pain because they have peripheral as well as central analgesic effects. If moderate to severe pain is not relieved with either NSAIDs or opiate analgesics given alone, combining analgesics for pain relief can certainly be considered. Additive toxicity must be monitored. If this is not effective, then adjuvant therapy for the malignancy itself may be indicated. For example, radiation therapy at sites of bone pain may be of profound benefit. In addition, administration of analgesics by another route (e.g., switching from subcutaneous to intravenous administration) may be effective. Sustained-release fentanyl patches may be helpful in some cases. Nerve blocks or other surgical procedures to alleviate discomfort can also be employed.
Fentanyl-impregnated patches [Duragesic, Janssen Pharmaceutica, Titusville, NJ] are now available as a transdermal patch that reliably releases a controlled amount of fentanyl over a 72-hour period (Figure 1). This relatively new device has practically revolutionized pain control in cancer patients. Since its release, the use of morphine pumps has declined. The patch boasts ease of use, portability, flexible dosing, and efficacy. Side effects are generally minimal or easily managed.
The transdermal fentanyl patch is indicated for chronic pain in cats with moderate to severe pain requiring constant analgesia. The active ingredient, fentanyl citrate, is approximately 75 times more potent than morphine, yet produces fewer histaminic side effects. Patches are available in strengths of 25, 50, 75, and 100 mcg per hour. Because of the cat's small size, only the 25 mcg per hour size is recommended. Transdermal fentanyl patches are efficacious. Since they need to be changed only every 72 hours, owners and veterinarians can attend to matters other than pain control; plus, having fewer dosing units in the house removes much of the problem of cohabitant abuse (when this is an issue).
In one study, fentanyl patches were applied to the skin of six cats, and blood samples for fentanyl analysis were collected over 104 hours. This study established that the transdermal patch technology is an effective, long-lasting, cost-effective, noninvasive, and well-tolerated mode of delivering fentanyl to cats. The TTS-Fentanyl Multicentre Study showed a reduction in nausea, vomiting, and constipation after conversion from oral narcotics, and breakthrough morphine dosing declined. For patients who cannot take oral medications, the advantage of a topical drug is obvious.
The disadvantages of the fentanyl patch include a lag period of 24 to 72 hours before peak levels are achieved. Also, typical opioid negative effects can be seen. Treatment of overdose consists of removing the patch and administering a naloxone bolus followed by a carefully monitored naloxone drip. Obviously, this sort of intervention is best avoided altogether; proper and careful dosing and titration is the key.
