A muscle relaxant is a drug that affects skeletal muscle function and decreases the muscle tone.
It may be used to alleviate symptoms such as muscle spasms, pain, and hyperreflexia. The term “muscle relaxant” is used to refer to two major therapeutic groups: neuromuscular blockers and spasmolytics. Neuromuscular blockers act by interfering with transmission at the neuromuscular end plate and have no central nervous system (CNS) activity.
They are often used during surgical procedures and in intensive care and emergency medicine to cause temporary paralysis. Spasmolytics, also known as “centrally acting” muscle relaxants, are used to alleviate musculoskeletal pain and spasms and to reduce spasticity in a variety of neurological conditions. While both neuromuscular blockers and spasmolytics are often grouped together as muscle relaxants, the term is commonly used to refer to spasmolytics only.
How Skeletal Muscle Contracts
A single α-motor neuron can innervate up to 200 muscle fibers, forming a complex called motor unit (Figure 1).10 With movement, an action potential originates from the UMN in the motor cortex.9 This action potential depolarizes the motor neuron terminal, resulting in the opening of voltage-gated calcium (Ca2+) channels and the subsequent release of the neurotransmitter acetylcholine (Ach) into the synaptic cleft. In the synaptic cleft, Ach binds to nicotinic cholinergic receptors on the muscle fiber membrane, leading to an influx of sodium (Na+) and a discharge of potassium (K) across the muscle fiber’s membrane, which results in depolarization of the muscle fiber.11 This depolarization opens voltage-gated Ca2+ channels on the sarcoplasmic reticulum (via ryanodine and inositol triphosphate receptors), allowing for Ca2+ influx into the cytoplasm of striated muscle cells.12 The Ca2+ then binds to troponin C, which exposes myosin-binding sites on actin filaments. A cross-link forms between actin and myosin, leading to muscle contraction. The pumping of Ca2+ back into the sarcoplasmic reticulum, using adenosine triphosphate, leads to cessation of contraction.
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---|---|---|---|
Antiflex Generic name: orphenadrine |
1 review |
|
10
|
Dantrium (Pro) Generic name: dantrolene |
2 reviews |
|
10
|
Vanadom Generic name: carisoprodol |
1 review |
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9.0
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Soma (Pro) Generic name: carisoprodol |
180 reviews |
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8.9
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Zanaflex (Pro) Generic name: tizanidine |
100 reviews |
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7.7
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Xeomin (Pro) Generic name: incobotulinumtoxinA |
2 reviews |
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7.5
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Amrix (Pro) Generic name: cyclobenzaprine |
48 reviews |
|
7.3
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Myobloc (Pro) Generic name: rimabotulinumtoxinB |
3 reviews |
|
7.2
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Skelaxin (Pro) Generic name: metaxalone |
82 reviews |
|
7.2
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Lioresal (Pro) Generic name: baclofen |
20 reviews |
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6.8
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Norflex (Pro) Generic name: orphenadrine |
22 reviews |
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6.5
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Flexeril (Pro) Generic name: cyclobenzaprine |
197 reviews |
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6.3
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Robaxin (Pro) Generic name: methocarbamol |
63 reviews |
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6.3
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Lorzone (Pro) Generic name: chlorzoxazone |
21 reviews |
|
6.2
|
Dysport (Pro) Generic name: abobotulinumtoxinA |
7 reviews |
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6.1
|
Botox (Pro) Generic name: onabotulinumtoxinA |
350 reviews |
|
5.9
|
Parafon Forte DSC (Pro) Generic name: chlorzoxazone |
3 reviews |
|
5.9
|
Fexmid (Pro) Generic name: cyclobenzaprine |
4 reviews |
|
5.8
|
Gablofen (Pro) Generic name: baclofen |
3 reviews |
|
5.8
|
Robaxin-750 Generic name: methocarbamol |
39 reviews |
|
5.6
|
Lioresal Intrathecal Generic name: baclofen |
3 reviews |
|
5.2
|
Botox Cosmetic (Pro) Generic name: onabotulinumtoxinA |
11 reviews |
|
4.9
|
Comfort Pac with Cyclobenzaprine Generic name: cyclobenzaprine |
2 reviews |
|
4.5
|
Orfro Generic name: orphenadrine |
0 reviews |
|
3.0
|
Kemstro Generic name: baclofen |
0 reviews |
|
2.0
|
Dantrium Intravenous (Pro) Generic name: dantrolene |
0 reviews | Add rating | |
Mio-Rel Generic name: orphenadrine |
0 reviews | Add rating | |
Orphenate Generic name: orphenadrine |
0 reviews | Add rating | |
Ozobax (Pro) Generic name: baclofen |
0 reviews | Add rating | |
Paraflex Generic name: chlorzoxazone |
0 reviews | Add rating | |
Remular-S Generic name: chlorzoxazone |
0 reviews | Add rating | |
Revonto (Pro) Generic name: dantrolene |
0 reviews | Add rating | |
Ryanodex (Pro) Generic name: dantrolene |
0 reviews | Add rating |
Further information
Muscle Spasms
A muscle spasm is a sudden involuntary contraction of a muscle group that involves jerking and twitching. Unlike spasticity, which is a disorder of the CNS, muscle spasms arise from a variety of peripheral musculoskeletal conditions, such as mechanical low back pain. Common skeletal muscle conditions that cause spasms include fibromyalgia, myofascial pain syndrome, and mechanical low back or neck pain.
Antispasm Agents
Most of the agents discussed here are FDA approved for adjunctive use to treat muscle spasms and pain associated with acute musculoskeletal conditions (Table 4). Health data from 2003 to 2004 revealed that cyclobenzaprine (Amrix, Fexmid, others), carisoprodol (Soma, others), and metaxalone (Metaxall, Skelaxin, others) accounted for more than 45% of medications prescribed for acute musculoskeletal pain.
Due to CNS depression, cyclobenzaprine, metaxalone, orphenadrine (Norflex, others), methocarbamol (Robaxin, others), carisoprodol, and chlorzoxazone (Lorzone, Parafon Forte DSC, others) are on the American Geriatrics Society’s Beers List of inappropriate drugs for elderly patients.
Despite this, approximately 300,000 annual prescriptions for skeletal muscle relaxants (15%) are issued to patients older than 65 years of age.
Skeletal muscle relaxants represent a diverse pharmacotherapeutic group of medications across several chemical classes that are structurally dissimilar. These agents are effective for spasticity, skeletal muscle spasms, or both.
Because of the breadth of pharmacologic mechanisms and variable pharmacokinetics, the drugs have a huge range of AEs and potential drug interactions.
Considering that these agents are most often used in the elderly and also as adjuvants for the treatment of chronic pain patients with multiple comorbidities who are likely receiving a polypharmaceutical regimen (including opioids), skeletal muscle drug selection for each patient requires careful attention to these factors.
Warnings for prescription muscle relaxants
Muscle relaxants such as carisoprodol and diazepam can be habit forming. Be sure to take your medication exactly as prescribed by your doctor.
Muscle relaxants can also cause withdrawal symptoms, such as seizures or hallucinations (sensing things that aren’t real). Do not suddenly stop taking your medication, especially if you’ve been taking it for a long time.
Also, muscle relaxants depress your central nervous system (CNS), making it hard to pay attention or stay awake. While taking a muscle relaxant, avoid activities that require mental alertness or coordination, such as driving or using heavy machinery.
You should not take muscle relaxants with:
- alcohol
- CNS depressant drugs, such as opioids or psychotropics
- sleeping medications
- herbal supplements such as St. John’s wort
Talk to your doctor about how you can safely use muscle relaxants if you:
- are older than 65 years
- have a mental health problem or brain disorder
- have liver problems
Off-label medications for spasticity
Doctors can use certain medications to treat spasticity even when the drugs are not approved for that purpose by the U.S. Food and Drug Association (FDA). This is called off-label drug use. The following drugs are not actually muscle relaxants, but they can still help relieve symptoms of spasticity.
Benzodiazepines
Benzodiazepines are sedatives that can help relax muscles. They work by increasing the effects of certain neurotransmitters, which are chemicals that relay messages between your brain cells.
Examples of benzodiazepines include:
- clonazepam (Klonopin)
- lorazepam (Ativan)
- alprazolam (Xanax)
Side effects of benzodiazepines can include drowsiness and problems with balance and memory. These drugs can also be habit forming.
Clonidine
Clonidine (Kapvay) is thought to work by preventing your nerves from sending pain signals to your brain or by causing a sedative effect.
Clonidine should not be used with other muscle relaxants. Taking it with similar drugs increases your risk of side effects. For instance, taking clonidine with tizanidine can cause very low blood pressure.
Clonidine is available in brand-name and generic versions.
Gabapentin
Gabapentin (Neurontin) is an anticonvulsant drug typically used to relieve seizures. It’s not fully known how gabapentin works to relieve muscle spasticity. Gabapentin is available in brand-name and generic versions.
Over-the-counter options for muscle spasms
OTC treatment is recommended as first-line therapy for muscle spasms caused by conditions such as acute lower back pain or tension headache. This means you should try OTC treatments before prescription medications.
OTC treatment options include nonsteroidal anti-inflammatory drugs (NSAIDs), acetaminophen, or a combination of both. Your doctor or pharmacist can help you choose an OTC treatment.
Nonsteroidal anti-inflammatory drugs (NSAIDs)
NSAIDs work by blocking your body from making certain substances that cause inflammation and pain. NSAIDs are available in generic and brand-name versions. They’re typically sold over the counter. Stronger versions are available by prescription.
NSAIDs come as oral tablets, capsules, or suspensions. They also come as chewable tablets for children. Side effects of these drugs can include upset stomach and dizziness.
Examples of NSAIDs include:
- ibuprofen (Advil, Motrin)
- naproxen (Aleve)
Acetaminophen
Acetaminophen (Tylenol) is thought to work by blocking your body from making certain substances that cause pain. Acetaminophen is available in generic and brand-name versions. It comes as immediate-release and extended release oral tablets and capsules, orally disintegrating tablets, chewable tablets, and oral solutions.
The more common side effects of acetaminophen can include nausea and upset stomach.
What are Skeletal muscle relaxants?
Skeletal muscle relaxants are drugs that are used to relax and reduce tension in muscles. They are more simply referred to as muscle relaxants.
Some work in the brain or spinal cord to block or dampen down excessively stimulated nerve pathways. These are called centrally acting muscle relaxants and examples include baclofen, methocarbamol, and tizanidine.
Others act directly on muscle fibers and are classified as peripherally acting muscle relaxants. Examples include dantrolene and the different types of botulinum toxin. Although dantrolene acts directly on the muscle itself, it also appears to indirectly act on the central nervous system and can cause drowsiness.
Cannabis extract also has muscle relaxing properties and is thought to act both centrally and peripherally.