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Pain

Management with Drugs

Basic Principles of Cancer Pain Management

The World Health Organization developed a 3-step approach for pain management based on the severity of the pain:

Acetaminophen and NSAIDs

NSAIDs are effective for relief of mild pain. They may be given with opioids for the relief of moderate to severe pain. Acetaminophen also relieves pain, although it does not have the anti-inflammatory effect that aspirin and NSAIDs do. Patients, especially older patients, who are taking acetaminophen or NSAIDs should be closely monitored for side effects. Aspirin should not be given to children to treat pain.

Opioids

Opioids are very effective for the relief of moderate to severe pain. Many patients with cancer pain, however, become tolerant to opioids during long-term therapy. Therefore, increasing doses may be needed to continue to relieve pain. A patient's tolerance of an opioid or physical dependence on it is not the same as addiction (psychological dependence). Mistaken concerns about addiction can result in undertreating pain.

Types of Opioids

There are several types of opioids. Morphine is the most commonly used opioid in cancer pain management. Other commonly used opioids include hydromorphone, oxycodone, oxymorphone, methadone, fentanyl, meperidine (Demerol), tapentadol, and tramadol. The availability of several different opioids allows the doctor flexibility in prescribing a medication regimen that will meet individual patient needs.

Guidelines for Giving Opioids

Most patients with cancer pain will need to receive pain medication on a fixed schedule to manage the pain and prevent it from getting worse. The doctor will prescribe a dose of the opioid medication that can be taken as needed along with the regular fixed-schedule opioid to control pain that occurs between the scheduled doses. The amount of time between doses depends on which opioid the doctor prescribes. The correct dose is the amount of opioid that controls pain with the fewest side effects. The goal is to achieve a good balance between pain relief and side effects by gradually adjusting the dose. If opioid tolerance does occur, it can be overcome by increasing the dose or changing to another opioid, especially if higher doses are needed.

Occasionally, doses may need to be decreased or stopped. This may occur when patients become pain free because of cancer treatments such as nerve blocks or radiation therapy. The doctor may also decrease the dose when the patient experiences opioid-related sedation along with good pain control, or when kidney failure develops or worsens.

Medications for pain may be given in several ways. When the patient has a working stomach and intestines, the preferred method is by mouth, since medications given orally are convenient and usually inexpensive. When patients cannot take medications by mouth, other less invasive methods may be used, such as rectally, through medication patches placed on the skin, or in the form of a nasal spray. Intravenous methods are used only when simpler, less demanding, and less costly methods are inappropriate, ineffective, or unacceptable to the patient. Patient-controlled analgesia (PCA) pumps may be used to determine the opioid dose when starting opioid therapy. Once the pain is controlled, the doctor may prescribe regular opioid doses based on the amount the patient required when using the PCA pump. Intraspinal administration of opioids combined with a local anesthetic may be helpful for some patients who have uncontrollable pain.

Side Effects of Opioids

Patients should be watched closely for side effects of opioids. The most common side effects of opioids include nausea, sleepiness, and constipation. The doctor should discuss the side effects with patients before starting opioid treatment. Sleepiness and nausea are usually experienced when opioid treatment is started and tend to improve within a few days. Other side effects of opioid treatment include vomiting, difficulty in thinking clearly, problems with breathing, gradual overdose, and problems with sexual function. Chronic nausea and vomiting in patients receiving long-term opioid treatment may be caused by constipation.

Opioids slow down the muscle contractions and movement in the stomach and intestines resulting in hard stools. The key to effective prevention of constipation is to be sure the patient receives plenty of fluids to keep the stool soft. Unless there are problems such as a blocked bowel or diarrhea, patients will usually be given a regimen to follow to prevent constipation and information on how to manage bowel health while taking opioids.

Patients should talk to their doctor about side effects that become too bothersome or severe. Because there are differences between individual patients in the degree to which opioids may cause side effects, severe or continuing problems should be reported to the doctor. The doctor may decrease the dose of the opioid, switch to a different opioid, or switch the way the opioid is given (for example intravenous or injection rather than by mouth) to attempt to decrease the side effects. (Refer to the PDQ summaries on Gastrointestinal Complications, Nausea and Vomiting, Nutrition in Cancer Care, and Sexuality and Reproductive Issues for more information about coping with these side effects.)

Drugs Used with Pain Medications

Other drugs may be given at the same time as the pain medication. This is done to increase the effectiveness of the pain medication, treat symptoms, and relieve specific types of pain. These drugs include antidepressants, anticonvulsants, local anesthetics, corticosteroids, bisphosphonates, and stimulants. A monoclonal antibody called denosumab is used to prevent broken bones and other bone problems caused by solid tumors that have metastasized (spread) to bone. There are great differences in how patients respond to these drugs. Side effects are common and should be reported to the doctor.

The use of bisphosphonates may cause severe and sometimes disabling pain in the bones, joints, and/or muscles. This pain may develop after these drugs are used for days, months, or years, as compared with the fever, chills, and discomfort that may occur when intravenous bisphosphonates are first given. If severe muscle or bone pain develops, bisphosphonate therapy may need to be stopped.

The use of bisphosphonates is also linked to the risk of bisphosphonate-associated osteonecrosis (BON). See the PDQ summary on Oral Complications of Chemotherapy and Head/Neck Radiation for more information on BON.