Skeletal Muscle Relaxers
Types of muscle relaxants
Skeletal muscle relaxants represent a heterogeneous group of agents that each has an overall sedative effect on the body. Muscle relaxants are used to treat muscle spasms and spasticity caused by various conditions. Both muscle spasms and spasticity involve involuntary muscular contraction that can bresult in severe pain. Muscle relaxants act in the central nervous system (CNS) to produce their muscle relaxing effects.
Historical background: Muscle relaxants were first used in poisoned arrows for hunting by South American Indians. It took several hundred years until their therapeutic benefit was realized and introduced in medicine. The first drug recognized to produce spasmolytic action was antodyne or 3-phenoxy-1,2-propanediol, however, its skeletal muscle relaxing effect was very short.
Muscle relaxers are prescribed for a variety of musculoskeletal conditions:
Muscle relaxers are classified as either antispasticity or antispasmodic agents.
The antispasticity agents help to improve muscle hypertonicity and contractions of muscles causing stiff or awkward movements (involuntary jerks). They alleviate spasticity by attempting to increase reflexes.
Antispasmodic muscle relaxants (spasmolytics) are mainly used to treat musculoskeletal conditions such as back pain, herniated disks, sciatica, spinal stenosis, and tetanus.
Back pain treatment
Currently, skeletal muscle relaxants are the most widely prescribed class of drugs for nonspecific back pain6. It is estimated that up to 91% of physicians report using muscle relaxants, and approximately 35% of patients visiting a primary care physician with the complaints of low back pain have them prescribed5.
Carisoprodol, cyclobenzaprine, orphenadrine, and tizanidine are moderately effective for short-term relief (two weeks) of acute low back pain1,2. For acute back pain, muscle relaxers can improve pain, muscle tension, and range of motion. They may provide additional improvement when used as adjunctive therapy with NSAIDs.
There is also some evidence that muscle relaxers can provide improvements in pain and function in patients with chronic low back pain. Tne main limiting factor in the use of muscle relaxants is a high incidence of drowsiness, dizziness and other sedative side effects.
Although not FDA approved for long term use, cyclobenzaprine is often prescribed nightly for the treatment of fibromyalgia. It may improve sleep, alleviate pain, and increase the sense of well-being.
The combination of carisoprodol, acetaminophen and caffeine is also used "off-label" for fibromyalgia. It can relieve pain, improve sleep, and reduce the general feeling of being sick 3. Carisoprodol produces its muscle relaxant effect at the spinal cord level.
Orphenadrine is a centrally acting analgesic muscle relaxant. It is used as an adjunct to rest, physical therapy and symptomatic measures for acute musculoskeletal pain. In clinical study 4 of 85 patients with fibromyalgia, over a one-year period a significant improvement in general pain was noted in 34% of participants taking orphenadrine citrate (vs. 15% and 10% of patients taking amitriptyline and cyclobenzaprine, respectively).