COMMENTARY

Using Muscle Relaxants in Chronic Pain

Charles E. Argoff, MD

Disclosures

April 27, 2012

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This is Dr. Charles Argoff. I'm Professor of Neurology and Director of the Comprehensive Pain Center at Albany Medical College and Albany Medical Center in Albany, New York. I would like to present a pretty common situation for all of us, which is addressing the role of muscle relaxants for patients who might need them for management of chronic pain.

Imagine a 42-year-old gentleman who is coming to see you with a chief complaint of low back pain as well as neck pain. Associated with those complaints is the absence of any neurological findings or any significant structural abnormalities revealed by any imaging test that you can possibly think of. You decide to use MRI, CT, or plain x-rays, and there are no neurological findings -- only significant active painful muscle spasm. Let's imagine that this all occurred after significant heavy work in the patient's backyard during gardening season.

What you are trying to do is address a 42-year-old gentleman with significant painful muscle spasm that occurred after a non-work-related injury. You are trying to manage his painful muscle spasm in the most effective way possible. It has been a few weeks since it hasn't responded to simple over-the-counter anti-inflammatory drugs.

I want to review some of the more commonly prescribed muscle relaxants to get an understanding of what is available and what to be cautious about. Let's look at cyclobenzaprine. The brand name of cyclobenzaprine is Flexeril. Cyclobenzaprine is a tricyclic antidepressant that failed in its development as an antidepressant and was subsequently redeveloped as a muscle relaxant. It is marketed in several forms, not only as Flexeril but also as Amrix. It is so structurally similar to amitriptyline that they differ by only a single double-bond. This is important because both amitriptyline and cyclobenzaprine share very important side effects, including the risk for sudden cardiac death, anticholinergic side effects, sedation, and others. It is very important to realize that when you prescribe cyclobenzaprine, you are prescribing a medication that is truly in the tricyclic antidepressant category. Keep that in mind when thinking about what other medications that patient may be using.

Another commonly prescribed muscle relaxant is carisoprodol, also known as Soma. It should be made clear that carisoprodol is now banned by the European Medicines Agency, the equivalent of the Drug Enforcement Administration, due to concerns about physical and emotional dependence on that medication. For those of you who do prescribe this drug, I would caution you that these risks are very real. One of the active metabolites of carisoprodol is meprobamate, which is a sedative-hypnotic agent that was sold under the name Miltown many years ago. Miltown was found in emergency department surveys to be frequently associated with misuse and overuse. Therefore, it is important to realize that what used to be fairly commonly prescribed as a muscle relaxant has some serious issues to consider.

Let's look at 2 older medications. One is methocarbamol, also known as Robaxin. The other is metaxalone, also known as Skelaxin. These agents were developed over 30 years ago and are the least likely among the commonly prescribed medications to produce sedation, although they can produce sedation. These agents are very reasonable to consider. They do have side effects that you should look for, including sedation, but they are not as likely to cause sedation as some of the others. These are reasonable medications to consider.

Another very commonly prescribed medication is orphenadrine, sold under the brand name Norflex. One should be aware of the fact that orphenadrine is actually a diphenhydramine, a Benadryl look-alike in terms of its activity and mechanism of action. This is extremely important to realize, not only because you should know what you're prescribing, but also because of the side-effect profile of this medication. As you are probably aware, diphenhydramine and orphenadrine can both produce sedation and motoric impairment that is comparable to using alcohol at certain levels. This is important if our goal in treating someone like this 42-year-old gentleman is to establish a regimen that will allow him to continue to function during the day.

Before ending this particular segment, I would like to turn to 2 medications that are not officially FDA-approved as muscle relaxants for acute or other care but which are used very frequently to treat spasticity because that is what they are approved for. The antispasticity medication tizanidine is sold under the brand name Zanaflex. What is neat about tizanidine is that, more than 20 years ago, it was shown in a study published in a British medical journal to be very effective in reducing pain associated with acute low back pain and acute musculoskeletal pain when combined with ibuprofen.[1] This is important because, although it is sold in this country and marketed as an antispasticity medication, there is very robust evidence for its use in chronic pain, chronic and acute musculoskeletal pain, and even chronic pain syndromes such as neuropathic pain. Tizanidine is an alpha-adrenergic agent similar to clonidine and has analgesic activity that you should be aware of. It is a sedating medication with a half-life of about 1.5 hours, so when given at night, it can help people wake up with much less spasm, much less tone, and not necessarily cause a "hangover effect" during the day. From a clinical perspective, I would only consider using tizanidine at night to help a patient sleep more comfortably with less muscle-related spasm pain and wake up more refreshed without a hangover effect.

The other medication that is marketed for spasticity is baclofen, brand name Lioresal. Baclofen can also be used for the treatment of musculoskeletal-related pain in an off-label manner. I have done that, and sometimes the other muscle relaxants are not particularly effective. Side effects, including sedation and others, need to be very carefully monitored because, especially for this 42-year-old gentleman, patients want to be as fully active as possible and work to their full potential. We don't want to prescribe medications that an individual may perceive as causing sedation.

Finally, just to remind ourselves that conservative care is very important: The use of other complementary medical therapies, such as topical or other anti-inflammatory drugs for painful muscle spasms and gentle and appropriate therapeutic exercise, can all work together to help muscle relaxants be more effective overall. I'm Dr. Charles Argoff. Thank you for your time.

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