One of the most useful classes of medications to relieve pain and suffering are the oral skeletal muscle relaxants (SMR). This column will discuss the different oral muscle relaxants, and precautions when taking these medications. It will focus on the SMRs that are typically used orally for muscle strains and injuries, not the neuromuscular blocking agents routinely used in surgical procedures.
The most commonly used SMRs are baclofen (Lioresal), carisoprodol (Soma), chlorzoxazone with acetaminophen (Parafon Forte), cyclobenzaprine (Flexeril), dantrolene (Dantrium), orphenadrine (Norflex),methocarbamol (Robaxin), metaxalone (Skelaxin), and tizanidine (Tizac).
Here are the dates that these drugs were approved by the FDA:
- Baclofen (11/22/1977)
- Carisoprodol (4/9/59)
- Chlorzoxazone (8/15/58)
- Cyclobenzaprine (8/26/77)
- Dantrolene (1/15/74)
- Orphenadrine (5/10/57)
- Methocarbamol (7/16/57)
- Tizanidine (11/27/96)
- Metaxalone (8/13/62)
Baclofen– can cause drowsiness, dizziness, weakness, and fatigue, as expected with a muscle relaxant. If one is on baclofen for a long period of time, say a few weeks, there may be withdrawal symptoms as with benzodiazepines and alcohol. If you are on this drug for an extended period of time it should be tapered when discontinued.
Carisoprodol– This drug was very popular when it was introduced as a muscle relaxant. It was glamorized and popularized by the comedian Milton Berle because it was sold under the brand name of Miltown, with the connection to “Uncle Milty”, who extolled the benefits of taking the drug. This should have been an expected consequence since carisoprodol, when metabolized in the body, becomes meprobamate, the first anti-anxiety drug. Meprobamate (FDA approved 4/28/55) was classified as a controlled substance 1970 because it was recognized that it has addicting characteristics. Also, as expected, carisoprodol (Soma) was made a controlled substance, but not until January 2012. The side effects are similar to other muscle relaxants, drowsiness, dizziness, fatigue, and the possibility of withdrawal symptoms if used for a long period of time. This is a drug that is wise to be tapered when discontinuing after a long use.
Chlorzoxazone- Even though this drug is not used much anymore it possesses the same side effect profile as other muscle relaxants, drowsiness, dizziness, weakness, and fatigue.
Cyclobenzaprine– The common brand name for this drug is Flexeril. It was derived from the class of drugs known as tricyclic, which are frequently used as antidepressants. As you can presume by now the major side effects are drowsiness, dizziness, weakness, and fatigue. Interestingly, it is being used off-label (not an officially approved indication by the FDA) to treat fibromyalgia, myofascial pain due to jaw disorders, and post-traumatic stress disorder (PTSD).
Dantrolene– This drug goes by the brand name Dantrium. It is not used often orally because its side effect profile includes speech and visual disturbances, mental depression and confusion, insomnia, and exacerbation or precipitation of seizures, yet it can cause sedation which would prohibit driving. Currently, dantrolene is mainly used as an IV treatment of a condition known as malignant hyperthermia. This condition occurs as a reaction to general anesthesia drugs during surgery. It is characterized by severe muscle rigidity, fever, and fast heart rate. Every institution that does surgery uses general anesthesia has an adequate supply of IV dantrolene to treat a malignant hyperthermia event. Previous to the use of dantrolene for malignant hyperthermia the mortality rate was 80%, now it is at 5% because of this drug.
Orphenadrine– This drug goes by the name of Norflex. It was derived from the antihistamine diphenhydramine, commonly known as Benadryl. As with all antihistamines their side effects are drowsiness, dizziness, weakness, and fatigue. In addition, dry mouth and urine retention can be expected with this drug.
Methocarbamol– This drug goes by the brand name of Robaxin and is one of the more widely used oral SMRs. By now we know that the side effect profile would include drowsiness, dizziness, weakness, and fatigue. Another characteristic that occurs occasionally is the turning of urine black, blue, or green. An interesting fact about this drug is that it is a chemical derivative of guaifenesin, which is used as an expectorant (loosens mucus to relieve coughing).
Tizanidine– This drug goes by the name Zanaflex. It has a side effect profile of other SMRs that include drowsiness, dizziness, weakness, and fatigue. It is suspected of having abuse potential but currently is not regulated as a controlled substance. An interesting fact about tizanidine is that it is chemically related to clonidine, which is used to lower blood pressure, treat ADHD, drug withdrawal, menopausal flushing, diarrhea, spasticity, and certain pain conditions.
Metaxalone– This drug goes by the brand name Skelaxin. By now it can be guessed that the side effect profile would include drowsiness, dizziness, weakness, and fatigue, and you would be correct. This drug is not used as often anymore, but is still available.
Another class of medications that can be used as SMRs are the benzodiazepines (Valium, Xanax, Ativan). These drugs, though effective as SMRs, are generally reserved for anxiety disorders, alcohol withdrawal, and seizures. This class of drugs should be used with great caution because of their addictive characteristics, and combination with other central nervous system depressing drugs, such as opioids, are dangerous. These drugs are usually not prescribed as a first line SMR.
After all this information, the take home points for using SMRs would be:
- Caution should be used because of the suppression of the central nervous system by these medications, which leads to decreased reflexes when operating machinery or driving.
- Since these drugs affect the central nervous system, they may have addicting characteristics.
- If a person is on one of these drugs it would be wise to taper the dose over a period of time upon discontinuing to prevent withdrawal symptoms, which are unpleasant.
- The different chemical families these drugs belong to are varied and suggest they work at different receptor sites and pathways to ease muscle tension.
I trust this article was informative and emphasizes the point that all medications should be taken with a degree of caution and respect.
Prosper and be in health.
What do you think?