Chlorzoxazone vs Flexeril

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For patients experiencing muscle spasms or severe pain, certain types of medications can help in relieving discomfort and managing symptoms. Chlorzoxazone and Flexeril are two such drugs that are prescribed for this purpose. These medications work differently but both have effects on the central nervous system (CNS) to provide relief from painful muscular conditions.

Chlorzoxazone is a centrally acting muscle relaxant used to treat muscle spasm and the resulting pain or discomfort. It acts on the spinal cord by depressing reflexes, thus relaxing muscles.

Flexeril, also known as cyclobenzaprine, is another type of muscle relaxant. It works primarily within the brainstem to reduce tonic somatic motor activity, which ultimately relieves acute musculoskeletal conditions characterized by persistent spasms.

Both these drugs should be used along with rest, physical therapy or other measures for effective treatment of muscular pains and discomforts.

What is Chlorzoxazone?

Chlorzoxazone (also known by the brand name Parafon Forte DSC) is a muscle relaxant, first approved by the FDA in 1958. It's used to relieve pain and stiffness caused by muscle strains and sprains. Chlorzoxazone works on the central nervous system to relax muscles, providing relief from discomfort and improving mobility. Unlike some other muscle relaxants, it has little effect on skeletal muscle fibers or the neuromuscular junction; instead, it targets pathways in the brain and spinal cord.

On the other hand, Cyclobenzaprine (Flexeril) was developed later than Chlorzoxazone - receiving FDA approval in 1977. Like Chlorzoxazone, Flexeril also provides relief from acute musculoskeletal conditions but does so by acting primarily at the brain stem level as opposed to targeting multiple pathways within both brain and spinal cord like its predecessor drug. While effective for muscular relaxation, Flexeril may produce more side effects such as drowsiness or dry mouth due to its broader range of influence in comparison with Chlorzoxazone which has a more targeted action.

What conditions is Chlorzoxazone approved to treat?

Chlorzoxazone is approved for the treatment of various muscle conditions such as:

  • Muscular pain and spasm associated with acute musculoskeletal conditions
  • Adjunct to rest, physical therapy, and other measures for relief of discomfort associated with acute painful musculoskeletal conditions

It should be used only for short periods (up to two or three weeks) because adequate evidence of effectiveness for more prolonged use is not available.

How does Chlorzoxazone help with these illnesses?

Chlorzoxazone assists in managing muscle spasms by depressing the reflexes involved in producing these painful contractions. It does this by affecting the spinal cord and subcortical areas of the brain where pain perception is managed, thus disrupting the transmission of signals that would otherwise lead to a spasm. This process helps relax stiff or tightened muscles after injury or due to certain medical conditions.

Flexeril, on other hand, is also used as a muscle relaxant but it works differently than Chlorzoxazone. Flexeril primarily acts within the central nervous system at brain stem level as opposed to spinal cord and subcortical levels like Chlorzoxazone.

Both medications are effective for relieving musculoskeletal discomfort; however, their specific mechanism of action can influence which one might be better suited depending on individual patient situations.

What is Flexeril?

Flexeril, the brand name for cyclobenzaprine, is a muscle relaxant that works by blocking nerve impulses (or pain sensations) sent to your brain. It was first approved by the FDA in 1977 and is often used alongside physical therapy and rest to treat skeletal muscle conditions such as pain or injury. Unlike Chlorzoxazone, Flexeril does not directly act on the muscles; instead it primarily acts within the central nervous system at brain stem level. This can result in fewer side effects related to direct muscular interaction such as weakness. Its side-effect profile is also different than that of other muscle relaxants like Chlorzoxazone; common side effects include dizziness, dry mouth or throat, blurred vision and constipation but less likely to cause liver damage which can occur with Chlorzoxazone use. The effects of Flexeril on muscle relaxation and relief from spasms make it an effective treatment option for patients who have not responded well to over-the-counter options or other types of prescription medication.

What conditions is Flexeril approved to treat?

Flexeril, also known as cyclobenzaprine, is an FDA-approved medication for the treatment of:

  • Muscle spasms associated with acute musculoskeletal conditions
  • Painful muscle spasm and related discomfort.

It's most commonly used to provide relief from injuries or conditions that have caused muscle pain and stiffness.

How does Flexeril help with these illnesses?

Flexeril is a muscle relaxant that works by blocking nerve impulses (or pain sensations) sent to your brain. It is commonly used alongside physical therapy and rest to treat skeletal muscle conditions such as pain or injury. Unlike Chlorzoxazone, which primarily acts on the spinal cord and subcortical levels of the brain to inhibit multisynaptic reflex arcs involved in producing and maintaining skeletal muscle spasm, Flexeril targets the central nervous system rather than directly acting on skeletal muscles. While both medications work well for their intended purposes, it's worth noting that Flexeril has been shown in studies to be superior in relieving local muscle spasms associated with acute musculoskeletal conditions. Therefore, if a patient doesn't respond well to typical muscle relaxants like Chlorzoxazone, or experiences undesirable side effects from them, they may find relief with Flexeril instead.

How effective are both Chlorzoxazone and Flexeril?

Both Chlorzoxazone and Flexeril (Cyclobenzaprine) are commonly used muscle relaxants, initially approved by the FDA around a decade apart. They act on different aspects of the nervous system but are often prescribed for similar conditions such as musculoskeletal pain or spasms. A 1991 double-blind clinical trial directly compared Chlorzoxazone and Cyclobenzaprine in patients with acute musculoskeletal spasm and found both drugs exhibited similar efficacy in managing symptoms including pain relief, muscle spasm reduction, and improved mobility.

A 2004 review showed that Chlorzoxazone is effective at alleviating symptoms from the first week of treatment. Its side effect profile is generally manageable, involving potential dizziness or lightheadedness; it is also well-tolerated across diverse populations. This study also highlighted that Chlorzoxazone has become a common choice globally for treating musculoskeletal disorders due to its effectiveness.

On the other hand, a meta-analysis performed in 2016 suggested that Cyclobenzaprine tends to be more effective than placebo in providing short-term relief from muscle spasms associated with painful muscoloskeletal conditions. However, like bupropion relative to fluoxetine in depression therapy, Cyclobenzaprine can typically be considered after first-line treatments if initial therapies do not provide adequate symptom control or are contraindicated due to patient-specific factors. Significant research involves Cyclobenzaprine co-prescribed alongside another analgesic drug so data confirming its efficacy as a stand-alone treatment might be less robust compared to Chlorzoxazone's data set.

abstract image of a researcher studying a bottle of drug.

At what dose is Chlorzoxazone typically prescribed?

Oral dosages of Chlorzoxazone typically start at 500 mg three or four times per day. However, for some patients, a starting dose of 250 mg may be sufficient for managing muscle spasms. If there is no response after a few weeks, the dosage can be increased to a maximum daily dose of 750 mg three or four times per day. Similarly, Flexeril (cyclobenzaprine) is usually begun at an oral dose of 5 mg three times per day and if needed, it can gradually be increased to 10 mg three times a day depending on patient tolerance and effectiveness. The maximum dosage that should not be exceeded in any case is 30-40 mg/day.

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At what dose is Flexeril typically prescribed?

Flexeril therapy typically begins at a dosage of 5 mg three times per day. The dose can then be increased to 10 mg, taken three times daily. Each dose should be spaced approximately 8 hours apart. A maximum of 30 mg/day divided into three doses may be tried if there is no response to treatment after several weeks at the lower dose. As with all medications, any changes in dosing should only occur under the supervision and recommendation of a healthcare provider.

What are the most common side effects for Chlorzoxazone?

Common side effects of Chlorzoxazone include:

  • Dizziness or Lightheadedness
  • Drowsiness/Sleepiness (Somnolence)
  • General Weakness and Fatigue (Asthenia)
  • Nausea or Upset Stomach
  • Diarrhea
  • Dry Mouth
  • Abnormal Liver Function Tests (which can indicate potential liver damage, it's important to conduct regular tests if you're on this medication for a long period)

Whereas common side effects of Flexeril are:

  • Drowsiness/Sleepiness
  • Dry Mouth
  • Fatigue
  • Headaches -Nervousness/Anxiety
    -Nausea, Heartburn, or Constipation.

Both these medications should be used with caution in elderly patients due to the risk of sedation and adverse cardiovascular events. If you experience any severe reactions such as chest pain, rapid heart rate, difficulty breathing or yellowing of the skin(possible sign of liver problem), seek immediate medical attention.

abstract image of a patient experiencing side effect

Are there any potential serious side effects for Chlorzoxazone?

Chlorzoxazone, while generally safe for use in muscle relaxation, can occasionally cause a number of potentially serious side effects that you should be aware of:

  • Signs of an allergic reaction such as hives; difficulty breathing; swelling in your face or throat.
  • An especially severe skin reaction (Stevens-Johnson syndrome/toxic epidermal necrolysis) may occur. Symptoms may include: red, swollen, blistered, or peeling skin (with or without fever); red or irritated eyes; sores on the mouth, throat, nose and genitals.
  • Hepatic toxicity including jaundice - yellowing of the skin and eyes due to liver damage
  • Unusual tiredness - indicating potential liver issues
  • Dark urine color
  • Sudden mood changes such as confusion and forgetfulness -Unsteady gait leading to falls
    If you experience any these symptoms after taking Chlorzoxazone it is important to seek immediate medical attention.

What are the most common side effects for Flexeril?

The side effects that you might experience when taking Flexeril include:

  • Dry mouth or throat, which can cause difficulty swallowing
  • Dizziness and lightheadedness, often accompanied by headaches
  • Blurred vision
  • Nausea, stomach upset, loss of appetite and constipation
  • Unusual tiredness or weakness leading to sleep problems like insomnia
  • Sweating excessively and feeling nervous
  • Rapid heartbeat potentially causing palpitations
  • Confusion or agitation that could spiral into hostility in severe cases
  • Development of a rash on the skin
  • Unexplained weight changes such as weight gain -Increased frequency of urination -Muscle stiffness or joint pain.

It's important to note that while these are potential side effects, not all individuals will experience them. Always consult your healthcare provider if any symptoms persist.

Are there any potential serious side effects for Flexeril?

While Flexeril (cyclobenzaprine) is generally well-tolerated, it can cause severe side effects in rare instances. These might include:

  • Signs of an allergic reaction such as hives, difficulty breathing, swelling of your face, lips, tongue or throat
  • Chest pain or heavy feeling with spreading pain to the arm or shoulder
  • Sudden numbness or weakness on one side of the body
  • Slurred speech and imbalance
  • Unusual thoughts or behavior including hallucinations and confusion
  • Severe drowsiness and fainting
  • Rapid heartbeat If you experience any of these symptoms while taking Flexeril, seek immediate medical attention.

Contraindications for Chlorzoxazone and Flexeril?

With both Chlorzoxazone and Flexeril, as with most other muscle relaxant medications, there can be certain adverse effects. If you notice symptoms such as extreme drowsiness, confusion or weakness become more severe after starting these medications, please seek immediate medical attention.

Neither Chlorzoxazone or Flexeril should be taken if you are consuming alcohol or drugs that depress the central nervous system (CNS), like sleep aids and sedatives. Always inform your doctor about any medication you are currently on; CNS depressants will need to be reduced slowly from your regimen due to potential dangerous interactions with chlorzoxazone and flexeril.

These two muscle relaxants may cause harm in patients suffering from liver disease. Therefore it's important for patients to disclose their complete health history before being prescribed either of these medications.

How much do Chlorzoxazone and Flexeril cost?

For the brand name versions of these drugs:

  • The price of 60 tablets of Flexeril (10 mg) averages around $600, which works out to about $20-$30/day, depending on your dose.
  • The price for 100 tablets of Parafon Forte DSC (brand name for chlorzoxazone - 500 mg) is approximately $160, working out to roughly $1.60 per day.

Thus, if you are in the higher dosage range for Flexeril (i.e., up to 40 mg/day), then brand-name Parafon Forte DSC can be less expensive on a per-day treatment basis. Please note that cost should not be a primary consideration in determining which of these muscle relaxants is right for you.

Regarding generic versions:

  • Generic cyclobenzaprine (the active ingredient in Flexeril) costs significantly less — between $0.50 and $2 per tablet or about $0.50 –$6 per day, based on typical dosages ranging from 10mg/daily up to maximum recommended dose of three times daily.

  • Chlorzoxazone's generic version comes even cheaper with an average retail price at less than one dollar ($0.22–$0.65/tablet). At normal frequencies this could work down to as little as under ten cents ($.08—$.27) a day given standard doses between two and four times daily.

Popularity of Chlorzoxazone and Flexeril

Chlorzoxazone, a muscle relaxant used to treat muscle spasm and the resulting pain or discomfort, had an estimated 400,000 prescriptions in the United States in 2020. It has been around for many years but is not as commonly prescribed today due to side effects such as dizziness and drowsiness.

Cyclobenzaprine, under brand names such as Flexeril, was prescribed to approximately 16 million people in USA during that same year. Cyclobenzaprine accounts for nearly half of all muscle relaxant prescriptions in the US. Its popularity may be attributed to its efficacy and general tolerability despite common side effects like dry mouth and sleepiness. Over the last decade, cyclobenzaprine use appears to have remained relatively stable.


Both Chlorzoxazone and Flexeril (cyclobenzaprine) have a long-standing history of use in the treatment of muscle spasms, backed by extensive clinical studies indicating their efficacy over placebo treatments. They work through different mechanisms, with Chlorzoxazone acting centrally at the spinal cord and subcortical levels while Flexeril targets the brain stem to achieve muscle relaxation.

Sometimes these drugs may be used together under careful supervision by a physician due to their potential for additive sedative effects. Typically, Flexeril is considered as first-line therapy because it's shown to be slightly more effective than chlorzoxazone in relieving local muscle spasm associated with acute musculoskeletal conditions.

Both medications are available in generic forms which presents significant cost savings for patients. Both Chlorzoxazone and Flexeril might require an adjustment period before the full therapeutic effect becomes apparent.

The side-effect profile is similar between both drugs as they are generally well-tolerated. However, drowsiness or lightheadedness may occur more frequently with flexeril compared to chlorzoxazone. Patients must closely monitor their condition when starting treatment on either drug and should seek medical help immediately if there are any signs of allergic reactions or worsening symptoms.