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Adjuvant meds for chronic pain

By Louis Neipris, M.D., Staff Writer, myOptumHealth

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What do drugs for depression and for epilepsy have in common? Both are sometimes prescribed for chronic pain. These and other drugs are known as adjuvant pain medications. This ever-expanding arsenal of pain-relieving drugs also includes muscle relaxants, topical anesthetics and steroids. This is promising news to those who are still in pain despite taking typical pain medications.

What are adjuvant pain medications?

An adjuvant pain drug is a medication used mainly for another condition but can also be prescribed for pain. It is used when the first choice of drug does not fully relieve pain. Adjuvant pain drugs are often prescribed in combination with typical pain-killing drugs such as NSAIDs or opioids.

How effective are they against pain?

Some studies show these drugs are effective against some types of pain when used alone or together with other medications. But adjuvant pain drugs may or may not be FDA-approved for use in pain. Many of them are prescribed "off label." That means that the FDA has approved them for another condition, such as depression or epilepsy, but they are not yet approved for treating chronic pain.

What are the different types of adjuvant pain medications?

There are several different categories. Antidepressants and anti-seizure drugs are the most common types of adjuvant pain medications.

Antidepressants for pain

Antidepressants were first prescribed to relieve the depression that often goes along with chronic pain. Doctors soon found that these drugs had their own painkilling effect and worked even in people who were not depressed. Antidepressants are thought to work by raising levels of neurochemicals in the brain that inhibit pain.

There are two categories of antidepressants used for chronic pain:

• Tricyclic antidepressants. Examples are amitriptyline (Elavil), nortriptyline (Aventil, Pamelor) and desipramine (Norpramin). These often help against nerve pain conditions, such as diabetic neuropathy and trigeminal neuralgia. They can also be used for fibromyalgia, rheumatoid arthritis, osteoarthritis and low back pain. They are used at a lower dose than that prescribed for depression, but may still have side effects.
• Selective serotonin reuptake inhibitors (SSRIs). These antidepressants may work as well against pain, but they have fewer side effects than the tricyclics. One drug in this class, duloxetine (Cymbalta) has recently been approved by the Food and Drug Administration (FDA) to treat the pain of diabetic neuropathy.

Tricyclic antidepressants may have side effects that can include:

• Cardiac arrhythmias (irregular heart rhythm)
• Urinary retention
• A tendency to faint when standing up
• Weight gain.

They may not be right for you if you are older or have a heart condition. There are fewer side effects associated with the SSRIs.

Anti-seizure medications used for pain

Drugs used to treat epilepsy have been used against pain for decades. This is especially true for nerve pain, which is described as burning or knife-like. They may work by quelling the bursts of electrical activity the nervous system generates when it is damaged.

Pregabalin (Lyrica) is FDA-approved for use in diabetic neuropathy, shingles and fibromyalgia. Clinical trials also show that gabapentin (Neurontin) may help with neuropathic pain.

Common side effects of these medications include mental clouding and sleepiness.

What other types of medications are used for pain?

Muscle relaxants, topical agents and corticosteroids are among the other types of adjuvant pain medications.

• Muscle relaxants relieve muscle stiffness and rigidity (spasticity) seen in conditions like cerebral palsy, multiple sclerosis or stroke. It can be a cause of chronic pain in these conditions. Muscle relaxants are also sometimes prescribed for acute low back pain.
• Topical agents are applied directly to the skin. Usually not as much is absorbed by the body, so there may be fewer side effects. The FDA approved the topical lidocaine patch (Lidoderm) for the treatment of shingles. Capsaicin cream is also used to relieve the pain of shingles as well as diabetic neuropathy. But it can cause a temporary burning or stinging sensation, and only a small amount should be applied at one time.
• Corticosteroids, such as dexamethasone and prednisone, reduce inflammation and can help ease some forms of nerve and bone pain. Side effects include increased appetite and fluid retention (short-term use), weight gain, "moon face" and osteoporosis (long-term use).

View the original Adjuvant meds for chronic pain article on myOptumHealth.com 

SOURCES:

• American Geriatrics Society Clinical Practice Guideline: Pharmacological management of persistent pain in older persons. (2008). Accessed: 06/02/2009

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• American Cancer Society. Cancer pain treatments. Adjuvant therapy. Accessed: 06/02/2009

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• Barkin RL, Schwer WA, Barkin SJ. Pharmacotherapeutic management of acute and chronic pain. In: Rakel RE. Rakel: Textbook of Family Medicine. 7th ed. Philadelphia, PA: Saunders Elsevier; 2007.

• Perrot S, Javier RM, Marty M, Le Jeune C, Laroche F. Anti-depressant use in painful rheumatic conditions. Rheumatic Disease Clinics of North America. 2008;34(2):433-453.