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.

CONCLUSION

Transdermal fentanyl is an efficacious therapy for chronic and some acute pain in the cat, especially in the terminal setting. Its benefits include portability, infrequent dosing, manageable side effects, non-oral administration, and efficacy comparable to morphine. Negatives include cost, the possibility of typical opioid adverse effects, and slow peak time. Its ease of use and client and patient satisfaction should encourage all practitioners dealing with severe chronic and some acute pain to familiarize themselves with its use.

GENERAL CONCEPTS OF PAIN THERAPY

Recent research has demonstrated that once pain is elicited, there is a magnification of the pain response Therefore, when compared to "on demand" therapy, the premeditated, judicious use of analgesics, including the fentanyl patch, is more likely to increase patient comfort, decrease need for hospitalization and subsequent expense, and reduce the amount of pain medication used to achieve the same level of comfort. Thus whenever possible, preventative therapy should be used as opposed to trying to suppress pain once it becomes a serious clinical problem. On the other hand, because fentanyl results in slow postoperative warming, parenteral administration of fentanyl and application of the patch shortly after surgery is often practiced.

Pain management begins with good quality compassionate care. Careful nursing with gentle handling of the patient and providing an environment that is comfortable and relaxing are of great benefit. Local anesthesia should be employed whenever possible to alleviate local discomfort. Systemic analgesia should be employed whenever there is a possibility that the discomfort is not localized or cannot be treated with local analgesia.

Mild Pain

Mild pain may be quite effectively treated with regular doses of NSAIDs (not Tylenol, and caution with aspirin!). These drugs do not cause central nervous system toxicity because they work peripherally, but can cause gastrointestinal upset. Although they are quite effective, they are not perceived by owners as having a significant analgesic effect and therefore may be dismissed as useful drugs. Fentanyl patches are not indicated for these patients.

MECHANISM OF CANCER PAIN

The most common mechanism of cancer pain is associated with tumor invasion and subsequent tissue damage that activate pain receptors. Therapy can also be associated with pain induction. For example, although surgery and radiation therapy can relieve pain and suffering, they can also cause significant discomfort due to tissue and nerve damage. Alkaloids such as vincristine and vinblastine can produce polyneuropathy, which has been noted to be painful in human cancer patients.

The types of cancer pain include visceral pain, inflammatory and somatic pain, neuritis, and neuropathic pain.

Visceral Pain

Visceral pain is a dull, deep, constantly aching pain. It is also poorly defined and often responds best in human patients to narcotic analgesics when pain is significant. Whether fentanyl is helpful in these cases is unknown; however, ileus is a possible complication of fentanyl use.

Inflammatory and Somatic Pain

Inflammatory and somatic pain is frequently described as well localized, constant, and aching. Common sources of this type of pain include bone metastases, tissue damage, and musculoskeletal, dental, and integument pain. In humans, this type of discomfort responds well to analgesics such as aspirin, acetaminophen, or the nonsteroidal anti-inflammatory drugs (NSAIDs). Fentanyl patches may be of value.

Neuritic Pain

Inflammation of nerves or nerve roots, which can be a paraneoplastic syndrome or a direct effect of cancer compression, causes neuritic pain. Humans describe this as a constant dull aching pain that may have periods of burning "shock-like" sensations.

Neuropathic Pain

Neuropathic pain is the result of a damaged segment of the nervous system that normally transmits pain stimuli. This is due to metabolic, immunologic, or direct physical effects on the nervous system. It is difficult to control with standard analgesics. Fentanyl is no exception.