Pain Relievers - Analgesics
In some cases, treating the underlying disorder eliminates or minimizes the pain. For example, setting a broken bone in a cast or giving antibiotics for an infected joint helps reduce pain. However, even if the underlying disorder can be treated, pain relievers (analgesics) may still be needed to quickly manage the pain. Doctors choose an analgesic based on the type and duration of pain and on the likely benefits and risks. Most analgesics are effective for nociceptive pain but are less effective for neuropathic pain, which often requires different drugs. For some types of pain, especially chronic pain, nondrug treatments are also important.
Analgesics fall into three categories: opioid (narcotic) analgesics, nonopioid analgesics, and adjuvant analgesics (drugs that are usually given for reasons other than pain but that sometimes relieve pain).
Opioid Analgesics
Opioid analgesics (narcotics), the most powerful analgesics, are the mainstay for treatment of severe acute pain and chronic pain due to cancer and other serious disorders. Opioids are preferred because they are so effective in controlling pain. The use of opioids to treat chronic pain not due to cancer is becoming more acceptable but is still relatively uncommon. Opioids are not appropriate for everyone.
Opioids are all chemically related to morphine, a natural substance extracted from poppies, although some opioids are extracted from other plants and other opioids are produced in a laboratory.
Opioids have many side effects. People who take opioids for acute pain often become drowsy. For some people, this drowsiness is welcome, but for others, it is not. Most people who take opioids become tolerant of this effect and do not continue to feel drowsy. Some people who continue to feel drowsy are given stimulant drugs, such as methylphenidate, to keep them awake and alert. Opioids may also cause confusion, especially in older people.
Opioids often cause constipation and retention of urine, especially in older people. Stimulant laxatives (see Bowel Movement Disorders: Laxatives), such as senna, help prevent or relieve the constipation. Increasing intake of fluids can also help.
Sometimes people with pain feel nauseated, and opioids can increase the nausea. Antiemetic drugs taken by mouth, suppository, or injection help prevent or relieve nausea. Some commonly used antiemetic drugs are metoclopramide, and prochlorperazine.
Taking too much of an opioid can have serious side effects, including a dangerous slowing of breathing and even coma. These effects can be reversed with naloxone, an antidote given intravenously. Nurses and family members should watch for side effects of opioids.
Doctors carefully weigh the benefits and side effects when they consider these drugs for the treatment of chronic pain. With repeated use of opioids over time, some people need higher doses because the body adapts to and thus responds less well to the drug; this phenomenon is called tolerance. For other people, the same dose remains effective for a long time.
People who take opioids for a long time usually become dependent on them; that is, they experience withdrawal symptoms if the drug is stopped. When opioids are stopped after long-term use, the dose must be gradually tapered to minimize the development of such symptoms. Dependence is not the same as addiction, which is the disruptive behavior or activity associated with obtaining and using the drug. Although addiction is possible, it appears to be rare among people who take opioids to control pain. Too often, exaggerated concern about the addiction potential of opioids (see Drug Use and Abuse: Opioids) leads to undertreatment of pain and needless suffering. People with severe pain should not avoid opioids, and adequate doses should be taken as needed.
When possible, opioids are taken by mouth. Opioids are given by injection when people cannot take them by mouth. For people who are helped by an opioid but cannot tolerate its side effects, an opioid can be administered directly into the space around the spinal cord through a pump, thus providing high concentrations of the drug to the brain. One opioid, fentanyl, is available as a skin patch. It provides pain relief for up to 72 hours.
Different opioid analgesics have different advantages and disadvantages. Morphine, the prototype of these drugs, can be taken by mouth (orally) or by injection. There are two oral forms: sustained-release and immediate-release. Different sustained-release forms provide relief for 8 to 24 hours. These drugs are widely used to treat chronic pain. The immediate-release form provides short-lived relief, usually for less than 3 hours. In injected forms, 2 to 6 times less morphine is required than in oral forms, because when morphine is taken by mouth, much of the drug is chemically altered (metabolized) by the liver before it reaches the bloodstream. Usually, the difference in the amount needed for the different routes does not change the effects of the drug. Pain relief with injected forms is quicker than that with oral forms, but relief does not last as long.
Morphine may be injected into a vein (intravenously), into a muscle (intramuscularly), or under the skin (subcutaneously). With the intravenous form of morphine, pain relief is almost immediate but does not last very long. With the intramuscular form, pain relief is less rapid but lasts somewhat longer. With the subcutaneous form, pain relief is the least rapid but lasts the longest.
Injections can be given every few hours, but repeated injections can become annoying. Alternatively, a catheter can be inserted in a vein or under the skin and connected to a continuous-infusion pump, which supplies morphine continuously. The continuous infusion can be supplemented with extra doses when needed. Sometimes a device that enables a person to control release of the drug by pressing a button is used. This technique is called patient-controlled analgesia. Usually, continuous infusion is used for people who have severe pain due to a serious disorder.
Opioids are essential to the management of acute pain. For example, opioid analgesics are usually prescribed after surgery. They are most effective when taken every few hours, before pain becomes severe. The dose may be increased, or another drug (such as a nonsteroidal anti-inflammatory drug) may be added if the pain temporarily worsens, if the person needs to exercise (movement can be more painful), or if the wound dressing is about to be changed. When the pain eases, doctors reduce the dose and prescribe nonopioid analgesics, such as acetaminophen.
Nonopioid Analgesics
A variety of nonopioid analgesics are available. Several (such as aspirin, ibuprofen, ketoprofen, naproxen) are available in prescription and nonprescription (over-the-counter, or OTC) strengths (see Over-the-Counter (OTC) Drugs: Analgesics and Nonsteroidal Anti-Inflammatory Drugs (NSAIDs)). Prescription-strength formulations contain more active ingredient per dose than OTC formulations. OTC analgesics are reasonably safe to take for short periods of time, but their labels caution against taking them for more than 7 to 10 days to treat pain. A doctor should be consulted if symptoms worsen or do not go away.
Nonsteroidal Anti-Inflammatory Drugs
Most nonopioid analgesics are classified as nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs are used to treat mild to moderate pain and may be combined with opioids to treat moderate to severe pain. NSAIDs not only relieve pain, but they also reduce the inflammation that often accompanies and worsens pain.
NSAIDs tend to irritate the stomach's lining and cause digestive upset (such as heartburn, indigestion, nausea, bloating, diarrhea, and stomach pain), peptic ulcers, and bleeding in the digestive tract. Coxibs (COX-2 inhibitors), a new type of NSAIDs, are less likely to irritate the stomach and cause bleeding than other NSAIDs.
Taking NSAIDs with food and using antacids may help prevent stomach irritation. The drug misoprostol can help prevent stomach irritation and ulcers, but it can cause other problems, including diarrhea. Proton pump inhibitors (such as omeprazole) or histamine-2 (H2) blockers (such as famotidine), which are used to treat peptic ulcers, can also help prevent stomach problems due to NSAIDs.
NSAIDs interfere with the clotting tendency of platelets (cell-like particles in the blood that help stop bleeding when blood vessels are injured). Consequently, NSAIDs increase the risk of bleeding, especially in the digestive tract if they also irritate the stomach's lining.
NSAIDs cause fluid retention and swelling in 1 to 2% of people. Regular use of NSAIDs may also increase the risk of developing a kidney disorder, sometimes resulting in renal failure (a disorder called analgesic nephropathy).
For older people, the risk of side effects due to NSAIDs is increased. For people who drink alcoholic beverages regularly and take NSAIDs, the risk of digestive upset, ulcers, and liver damage may be increased. People with heart failure, high blood pressure, or kidney or liver disorders require a doctor's supervision when they take NSAIDs. Some prescription heart and blood pressure drugs may not work as well when taken with these analgesics.
NSAIDs vary in how quickly they work and how long they relieve pain. Although NSAIDs are about equally effective, people respond to them differently; one person may find a particular drug to be more effective or to have fewer side effects than another.