1. Gastrointestinal-related pain associated with chemotherapy
The most common types of gastrointestinal (GI) pain in cancer patients are associated with vomiting, nausea, diarrhea, and pancreatitis. The degrees of pain from these can range from mild to severe. For vomiting or nausea, antiemetics are mainly used. Many of these drugs are 5-HT₃-receptor antagonists and have been proved to reduce or eliminate most chemotherapy-induced vomiting. This class of drugs works by effectively blocking 5-HT₃ receptors activated by serotonin, which can be released after chemotherapy administration. These receptors are located on the vagal afferent nerves and, in turn, initiate the vomiting reflex. Some veterinarians also prescribe butorphanol as an antiemetic or analgesic.

In patients experiencing diarrhea, depending on its severity, treatment can include administering metronidazole or oral famotidine, encouraging water intake, and offering bland and easy-to-digest foods (e.g. boiled chicken and rice). In severe cases, fluid therapy for both diarrhea and vomiting may be indicated. Intraperitoneal infusions of lidocaine along with systemic opioids may effectively control severe abdominal pain in hospitalized patients with pancreatitis that can result from treatment with certain chemotherapeutic agents. Note, studies show that general anesthesia alone causes pinpoint GI ulcers. This should be considered with patients requiring daily anesthesia.

2. Postoperative pain management
When dealing with pain caused by surgery, the best approach is a multimodal one. For amputations and thoracic surgeries, epidural catheters should be placed, and the patient should be treated with periodic infusions of morphine, lidocaine, or bupivacaine. This treatment is effective for up to 12 hours per injection and can be maintained safely for three to five days.

Most surgical systemic pain also can be treated with pharmacologic agents either as scheduled therapy or with a continuous-rate infusion of opioids, ketamine, or lidocaine. If the patient's renal and hepatic functions are normal, a nonsteroidal anti-inflammatory drug (NSAID) should be added to reduce inflammation. Ice packing the incision site (15 minutes each hour for the first 24-hour period) and using physical rehabilitation may alleviate postoperative pain. Keep in mind that devising PRN, or as needed orders, is an ineffective pain-management method because it may allow for pain to increase to an uncontrollable level.

A word of caution: Butorphanol isn’t considered an effective analgesic because its duration of analgesic effect is only 45 to 60 minutes. Also, the drug is extremely costly for most cases of immediate postoperative pain.¹

At-home treatments, which may include transdermal fentanyl patches and oral analgesics, such as acetaminophen with codeine, can be useful after pain is reduced to a moderate level. In cats, sublingual administration of buprenorphine is also an effective method to control minor to moderate pain.

Reference
1. Tranquilli WJ, Grimm KA, Lamont LA. Pain management for the small animal practitioner. Jackson, Wyo: Teton Press, 2000;4,7-10,14.