Pain Management

Pain is the unpleasant sensation that develops with the stimulation of specialized sensory nerve endings, called pain receptors. Pain most often develops from damage, irritation or inflammation of tissues or structures of the body. Pain is a protective mechanism. It causes the animal to react and to move away from the source of the stimulus.

Manifestations of pain are highly variable in animals. Some signs are obviously related to pain, while others are more subtle. The individual personality of the animal and its tolerance for pain also affect the clinical manifestations of pain. Animals in pain often present with a wide variety of signs. Some signs that are associated with pain include the following:

The purpose of pain management is not only to decrease the discomfort your dog feels, but to provide maintenance of quality of life. Pain management is directed at the source of the pain to control it, or used to change how the dog perceives the pain. There are both medicinal and non-medicinal methods of achieving pain control, and often times both modalities are combined in some way to attain the best result possible.

Non-Medicinal Modalities

Amputation

Amputation provides definitive pain relief. Amputation will restore quality of life, and in many cases, actually extend if, since dogs with severe pain from bone cancer are often euthanized at an early stage to end their suffering. Management of post operative pain can be successfully achieved with several of the modalities described herein.

Palliative Radiation

Palliative radiation is prescribed for those dogs who cannot undergo amputation. It can heal micro-fractures and decrease inflammation.

Debulking Surgery

In some cases, debulking surgery might be indicated to relieve pressure on vital structures and decrease tumor size. It is not a common procedure for bone cancer, but can be an option for soft tissue or joint tumors. This is done only for palliative pain relief.

Neurostimulation

The use of transcutaneous electrical nerve stimulation has been tried as a palliative approach to pain management. Similar to techniques used in humans, this technique involves the use of non-painful impulses that block the transmission of painful impulses along the nerves.

Acupuncture & Chiropractic Medicine

Also considered a palliative technique, and often combined with other modalities. There are many veterinarians that are certified in acupuncture and chiropractic care. www.animalchiropractic.org

Medicinal Modalities

Studies have shown that the continuous use of pain medications is more effective than using them “as needed”. Chronic pain is best managed with stable blood levels of the medication, avoiding a “see-saw” effect when the medicines are only given “as needed”. It is particularly difficult to assess when a dog actually needs the medication, since many of them are stoic and may not exhibit classic signs of pain on a regular basis (limping, decreased appetite, panting, decrease in mobility, etc). Administering the medications on a regular schedule may also allow for decrease in dosage, since the pain level is also decreased.

Non-Narcotic Pain Medications

Non Steroidal Anti-inflammatory Drugs

These include aspirin and other anti-inflammatory drugs, known as NSAIDs (non steroidal anti-inflammatory drugs). The most commonly used drugs in the NSAID category are carboprofen (Rimadyl®), etodolac, phenylbutazone, aspirin, deracoxib (Deramaxx®), piroxicam, and meloxicam (Metacam®), but others are available as well. Both the meloxicam and the carboprofen are available in injectable form as well.

NSAIDs work by inhibiting an enzyme called “cyclooxygenase”, which controls the amount of inflammatory substances known as prostaglandins. They can be used alone or in conjunction with narcotic medication to increase their effectiveness.

Gastrointestinal (GI) irritation in varying degrees is a common side effect with these medications. To minimize this side effect, stomach-protecting medications are often prescribed in conjunction with the NSAIDs. The most commonly used medications for this purpose are misoprostol and sucralfate. Other medications such as ranitidine (Pepcid®) or cimetidine (Tagamet®) have been used but are not as effective in preventing the GI side effects. These medicines are more effective if used once the damage to the GI tract has occurred. Symptoms can range from nausea and decreased appetite to bleeding in the GI tract. Dark, tarry or bloody stools, or vomiting blood or “coffee ground” material (indicating digested blood in the GI tract) are signs of bleeding in the GI tract and must be reported to the veterinarian immediately.

NSAIDs can also affect kidney and liver function, and should not be used in dogs with decreased liver or kidney function, or prior history of liver or kidney disease. Caution is recommended if NSAIDs are being prescribed along with other medications that may affect the liver or kidneys. This should be discussed with your veterinarian. Baseline kidney and liver function tests should be done before the medication is started, and should be repeated periodically while the dog is taking the medicine.

NSAIDs may affect clotting function by decreasing the way platelets stick to each other (this is known as platelet aggregation). Platelets are little blood cells that stick together to start formation of a blood clot, whenever there is tissue damage. This effect is reversible with NSAIDs and only lasts while the drug is in the system, however it is irreversible when aspirin is used, and will last for the life of the platelet cell. This effect of the NSAIDs may be exacerbated by the use of herbal anti-inflammatory medications or aspirin, and are not recommended to be used together. If your dog is taking any herbal medications, please consult with your primary or holistic veterinarian before combining these medicines.

In addition, several of the NSAIDs listed here are also used for their anti-angiogenic properties, which serves as an adjuvant in the management of cancer. “Anti-angiogenic” means that these medications may decrease the formation of new blood vessels in the cancer tissue, which in turn decreases the nutrients and rate of growth in the tumor.

Tramadol

Tramadol is a centrally acting analgesic that stimulates an opioid receptor in the brain, which provides pain relief. It is not a narcotic medication, and does not cause addiction. It has become a good addition to the pain management protocols that use NSAIDs. It has 1/10 the analgesic potency of morphine, and should not be prescribed in conjunction with morphine or fentanyl, because it will likely decrease the efficacy of those drugs. The brand name of tramadol is Ultram®.

It does not usually cause sedation but this is a possibility with higher doses or very sensitive dogs. T will rarely cause constipation and nausea. It should not be given to dogs who take Depreny for Cushings disease, dogs with cognitive disorders or dogs taking certain anti-depressant medications, including serotonin reuptake inhibitors (SSRIs) or monoamine oxidase inhibitors (MAOs). It is often used with NSAIDs and can be given to dogs who take steroids.

In human medicine there is a medication called Ultracet® which is a combination of tramadol with acetaminophen – this should not be given to dogs.

Narcotic Pain Medications

Butorphanol

Butorphanol is an opioid analgesic. In addition to its use for pain management, it is also used to induce sedation and to suppress coughing. It can be administered either by injection (Torbugesic®) or by pills (Torbutrol®). It should be used with caution in animals with an under active thyroid, kidney impairment, elderly or severe illness, and should be avoided in animals with head trauma or nervous system dysfunction. It is a short acting drug and is often administered several times a day.

Butorphanol may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving tranquilizers, barbiturates and antihistamines. The most significant side effects associated with butorphanol are sedation, lack of appetite and diarrhea.

Buprenorphine

Buprenorphine is a synthetic opiate that binds to opiate receptors and stimulates them. It is similar to one of the original opiates, morphine. It is 30 times as potent as morphine and does not result in the negative gastrointestinal effects typically associated with morphine. Although it is not approved for veterinary used, it can legally be prescribed for use as an “extra-label” drug. It is given via injection and its effect usually lasts 8 hours.

While generally safe and effective when prescribed by a veterinarian, buprenorphine can cause side effects, the most common one being sedation. It should be avoided in animals with kidney disease, underactive thyroid gland and Addison’s disease. It should be used with caution in animals with head trauma, compromised cardiovascular function and geriatric or severely debilitated animals. Since it is metabolized by the liver, buprenorphine should be used with caution in animals with liver disease. It may interact with other medications, such as certain antihistamines, tranquilizers, barbiturates and monoamine oxidase inhibitors. As with other opiates, in rare cases it can slow down breathing.

Morphine

Morphine is a well-known drug used to alleviate pain. It can affect various body functions: dogs may vomit after administration and will usually defecate immediately following injection. Panting may also occur. If necessary, the effects of the drug can be reversed with administration of naloxone. Although it is not approved for veterinary used, it can legally be prescribed for use as an “extra-label” drug. While its most common use is to treat pain, it can also be used to reduce coughing and diarrhea in dogs. Morphine should be used with extreme caution in cats. The enzyme that helps metabolize morphine is deficient in cats, which results in potential brain and spinal cord stimulation.

Morphine should be avoided in animals with liver disease, kidney disease, underactive thyroid gland, hyperactivity, toxin-induced diarrhea, victims of scorpion bites or Addison’s disease. It should be used with extreme caution in animals with head trauma, acute abdominal conditions and lung disease. It may interact with other medications, such as antihistamines, anesthetics, tranquilizers and monamine oxidase inhibitors.

Adverse effects associated with morphine include nausea, vomiting, slowed intestinal movement, constipation, restlessness, low blood pressure, slowed heart rate, slowed breathing, behavior changes and seizures. The most profound adverse effects associated with morphine are suppression of breathing and sedation.

Morphine can be administered by injection, oral tablets, oral solution and rectal suppositories.

Fentanyl

Fentanyl is a very potent opiate narcotic analgesic. It is 100 times as potent as morphine. The injectable form is used to sedate and tranquilize. The fentanyl patches (Duragesic®) are used for pain control. Doses of the patch range from 25 to 100 micrograms (not milligrams). The dose of fentanyl is based on the weight of the animal:

For very small animals, 1/2 of the patch can be used. The patch should NEVER be cut. Placing tape to cover 1/2 of the patch is sufficient to reduce the dose. Although it is not approved for veterinary used, it can legally be prescribed for use as an “extra-label” drug.

Other nervous system depressant drugs and sedatives must be used with caution when combined with fentanyl. As with most opiates, this drug can cause breathing activity to diminish. This can be a problem, especially if there is lung disease already present. Care must be taken when treating an animal with a fever or if using direct heat to the area. Increased body temperature can increase the amount of fentanyl absorbed and lead to overdosing. Fentanyl may interact with other medications, such as antihistamines, tranquilizers, barbiturates, other narcotics and monoamine oxidase inhibitors.

The patch should be applied to an area of the dog’s body that cannot be reached by licking or chewing. The pet must be prevented from eating a fentanyl patch. An overdose may result, leading to excessive sedation and depression. The area should be shaved or the hair clipped very close to the skin. Avoid areas that are irritated or otherwise damaged. The skin should be cleansed with alcohol and thoroughly dried before applying the patch. Once applied, the patch should then be held in place for 5 minutes, to allow body heat to activate the adhesive substance. It can be held in place with a bandage if necessary. A skin rash may develop at the site of the patch. The patch is only effective for three days and, if pain persists, the patch should be replaced following strict instructions by a veterinarian. Skin sites should be rotated to minimize accumulation in subcutaneous depots, which could result in erratic blood levels.

The more common side effects include sleepiness, constipation, dizziness and nausea. Less common side effects include difficulty breathing, confusion, tremors, vomiting, decreased breathing rate, and lack of coordination. Rare side effects include hiccups and hallucinations.

Amantadine