Muscle Relaxants

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Category	Prescription Drug	Strength	Quantity	Cost
Muscle Relaxants	Flexeril (cyclobenzaprine) Flextra (phenyltoloxamine) Skelaxin (metaxalone) Soma (carisoprodol) Zanaflex (tizanidine)	10 mg 500 mg 800 mg 350 mg 2 mg	30 pills 30 pills 30 pills 30 pills 30 pills	$48 $56 $130 $50 $55

Flexeril (cyclobenzaprine)

Flexeril is a muscle relaxant, used to treat the pain and stiffness of muscle injuries, including strains, sprains and muscle spasms. The active ingredient in Flexeril is cyclobenzaprine. Flexeril comes in 10 mg tablets, and the normal dose in adults is one 10 mg tablet three times daily. You should not exceed a total dosage of 60 mg of Flexeril per day.

Flextra DS (phenyltoloxamine and acetaminophen)

Flextra DS is an analgesic and antipyretic used to treat pain, muscle cramps, headache, fever and arthritis. Flextra is not a muscle relaxant but a pain reliever useful for muscle aches and joint pain. Flextra may make you dizzy or drowsy, so use caution when driving or using dangerous machinery.

Skelaxin (metaxalone)

Skelaxin is a muscle relaxant used to treat the pain and stiffness of muscle injury, strain, sprain and spasm. Use caution when driving or operating machinery as Skelaxin may cause dizziness and drowsiness.

Soma (carisoprodol)

Soma is a muscle relaxant used to relieve the pain and stiffness of muscle spasms and discomfort due to strain and sprain. The active ingredient in Soma is carisoprodol. The usual adult dosage of soma is one 350 mg tablet, three times daily and at bedtime. Usage in patients under age 12 is not recommended.

Zanaflex (tizanidine)

Zanaflex is used to help relax certain muscles in your body. It relieves the spasms and increased muscle tone caused by medical problems such as multiple sclerosis or spinal injury. Zanaflex comes as a tablet to be taken orally, usually two or three times a day.

Back pain is a common public health problem, affecting between 70% and 85% of adults at some time in their lives. In the US, back pain is the second most common cause of disability in the general population and the leading cause of disability among men. Approximately 45% of adults experience back pain annually, resulting in a substantial socioeconomic impact. Direct medical costs result from hospitalizations, outpatient services, physician visits and nursing home stays, while indirect costs include lost work and disability compensation.

Pharmacological and other treatments have been shown to reduce acute back pain and related symptoms, although there is less evidence of their effectiveness for chronic back pain. The use of pharmacological agents is vital because they serve to increase the efficacy of non-drug treatments, allowing for earlier mobilization and rehabilitation. Although this article does not represent a systematic search of the literature, we discuss a variety of pharmacological approaches to alleviating acute back pain and elaborate upon their advantages and disadvantages.

Pharmacological Therapy

Reducing paravertebral muscle spasm is a primary objective of pharmacological therapy for musculoskeletal back pain. The term “muscle relaxant” is very broad and refers to a variety of structurally unrelated medications. Muscle relaxants can be divided into two main categories:

1. Antispasmodic agents (the primary topic of this article) are used to treat musculoskeletal conditions associated with spasm. The exact mechanism of action of these drugs is often poorly understood; it is not clear whether these medications actually decrease muscle spasm or whether they exert other effects.

2. Antispasticity agents are used to decrease spasticity (contractions of muscles causing stiff or awkward movements as a result of a motor nerve problem) in neurological disorders, such as multiple sclerosis and spinal cord injuries.

A degree of overlap exists within these two categories; some medications are used in clinical practice for the treatment of both conditions. Tizanidine (Zanaflex®, Elan) and diazepam (Valium ®, Roche) are commonly prescribed for musculoskeletal spasm and are also approved for the treatment of spasticity.

Antispasmodic Drugs

Antispasmodics include medications of several different types, for example:

• antihistamines (orphenadrine, Norflex).
• central nervous system (CNS) depressants, chlorzoxazone (Parafon, Paraflex), metaxalone (Skelaxin), methacarbamol (Robaxin), and carisoprodol (Soma).
• central alpha2-adrenergic agonists (tizanidine, Zanaflex).
• tricyclic antidepressant compounds, such as cyclobenzaprine (Flexeril).
• gamma-aminobutyric acid (GABA) agonists (benzodiazepines, such as diazepam).

These medications have different indications and mechanisms of action. Consequently, drug actions and side effects may vary somewhat among the alternatives available. All antispasmodic agents can cause significant drowsiness to the extent that the manufacturers of these agents warn patients that activities requiring mental alertness (driving) may be impaired while they are taking the medication. Other potential adverse effects of this class of agents include dizziness, confusion, anorexia, nausea, vomiting, and allergic reactions. Because these drugs undergo hepatic metabolism and renal excretion, they must be used cautiously in patients with compromised liver or kidney function. Excessive doses may result in significant toxicity with CNS depression.

Orphenadrine

Orphenadrine citrate (Norflex®) is an analogue of the antihistamine diphenhydramine, which produces muscle relaxation by selectively blocking facilitatory functions of the reticular formation in the brainstem in animals. In addition, unlike other skeletal muscle relaxants, it produces some independent analgesic effects that may contribute to its efficacy in relieving painful skeletal muscle spasm. How this agent produces analgesia is unclear. The literature suggests that the analgesic effect of some antihistamines might have more than one mechanism of action, including modulation of nociceptive responses in histaminergic and serotoninergic pathways.

Chlorzoxazone

Chlorzoxazone acts primarily at the level of the spinal cord and subcortical areas of the brain, where it inhibits multisynaptic reflex arcs involved in producing and maintaining skeletal muscle spasm. The exact mode of action, although not clearly identified, may be related to the sedative properties of the drug.

Metaxalone

The effects of metaxalone (Skelaxin®) are similar to those of other antispasmodic medications. The exact mechanism of action has not been established, but it is probably a result of CNS depression with no direct effect on the contractile mechanism of striated muscle. Metaxalone is available as 400 and 800 mg tablets. The recommended adult dosage is 800 mg three to four times daily.

Methocarbamol

Methocarbamol (Robaxin®) has been marketed for the treatment of musculoskeletal pain since 1957. This medication is available in both oral tablets and parenteral formulations for IM and IV injection. A preparation containing aspirin (Robaxisal®, A. H. Robins) is also available. The drug’s mechanism of action probably involves general CNS depression. Methocarbamol has no direct effect on the contractile mechanism of striated muscle.

Carisoprodol

Carisoprodol (N-isopropylmeprobamate, Soma®) is a carbamate derivative that was first introduced in the late 1950s. It inhibits interneuronal transmission in the descending reticular formation and spinal cord and is thought to act via sedation rather than by direct skeletal muscle relaxation. Carisoprodol is available as 350 mg tablets. The recommended dosage is one tablet three times daily and one tablet at bedtime. It is also available combined with aspirin (Soma® Compound) and with aspirin and codeine (Soma® Compound with Codeine). The onset of action is rapid (within 30 minutes), and the duration of action is four to six hours. Carisoprodol is metabolized in the liver to hydroxycarisoprodol, hydroxymeprobamate, and meprobamate, which are excreted by the kidneys. The pharmacologically active metabolite, meprobamate, has a half-life of 11.3 hours, or up to 48 hours with chronic use. Because meprobamate is a controlled substance with a known potential for abuse, many clinicians have expressed concern about the potential of abuse of carisoprodol.

Cyclobenzaprine

Cyclobenzaprine (Flexeril®) is structurally and pharmacologically related to the tricyclic antidepressants and produces its effects within the CNS, primarily at the brainstem level. Tablets are available in strengths of 5 and 10 mg. The recommended dose is 10 mg three times per day. However, sedation may limit the dosage level in some patients. Like the tricyclic antidepressants, cyclobenzaprine has anticholinergic properties and may cause dry mouth, blurred vision, increased intraocular pressure, urinary retention, and constipation. It should not be used in patients with cardiac arrhythmias, conduction disturbance, or congestive heart failure or after myocardial infarction. Potentially dangerous interactions may occur with monoamine oxidase inhibitors. As with some antidepressants, withdrawal symptoms consisting of nausea, headache and malaise have been reported following abrupt cessation of cyclobenzaprine after prolonged use.

Drugs Used as Both Antispasmotic and Antispasticity Agents

Tizanidine

Tizanidine (Zanaflex®) is approved for the treatment of spasticity, and it is also used clinically to treat pain and spasm associated with muculoskeletal conditions. It is an agonist at alpha2-adrenergic receptor sites and presumably reduces spasticity by increasing presynaptic inhibition of the motor neurons without directly affecting skeletal muscle, the neuromuscular junction, or the monosynaptic spinal reflexes. Its effects are greatest on the polysynaptic pathways, and the overall effect of these actions is thought to reduce the facilitation of spinal motor neurons, resulting in muscle relaxation. At least five studies have demonstrated the usefulness of tizanidine for patients with musculoskeletal back pain and paravertebral muscle spasm. Side effects are similar to those seen with other skeletal muscle relaxants. Drowsiness was the most common reason for discontinuing the medication. Tizanidine has been associated with hepatic aminotransaminase elevations that are usually asymptomatic and reversible with cessation of therapy.

Benzodiazepines

Diazepam (Valium®) is also approved for the treatment of spasticity and is the most frequently prescribed benzodiazepine used for patients with paravertebral muscle spasm and musculoskeletal pain. Other available benzodiazepines have not proved superior to diazepam for this indication. The muscle-relaxant effects of this drug are thought to result from enhancement of GABA-mediated presynaptic inhibition at spinal and supraspinal sites. Diazepam also has antiepileptic, anxiolytic, and hypnotic properties. Studies comparing diazepam with placebo and other skeletal muscle relaxants have yielded inconsistent results. In general, diazepam has been found to be superior to placebo but not consistently superior to other skeletal muscle relaxants for the relief of muscle spasm and pain; however, it is more effective than other skeletal muscle relaxants that are approved for the treatment of musculoskeletal conditions when it is used to treat spasticity associated with CNS disorders (cerebral palsy and spinal cord injury). Its efficacy is similar to that of baclofen (Lioresal®, Novartis), tizanidine, and dantrolene sodium (Dantrium® , Procter & Gamble) for this problem.

Antispasticity Medications

Diazepam, tizanidine, baclofen, and dantrolene are approved for use in patients with spasticity. The latter two medications are not usually prescribed for paravertebral muscle spasm or musculoskeletal pain. However, because medications used to treat spasticity are also referred to as skeletal muscle relaxants, we briefly mention them here.

Baclofen

Baclofen (Lioresal®) is a chemical analogue of GABA (an inhibitory neurotransmitter) that acts primarily by inhibiting synaptic transmission in the spinal cord and, probably, in the supraspinal regions. It is used mainly in the management of spasticity secondary to CNS lesions, such as multiple sclerosis and spinal cord lesions. Baclofen is equivalent to tizanidine, diazepam, and dantrolene in reducing spasticity. It causes less sedation than diazepam or tizandine, but it may be associated with more weakness. It is not associated with the serious hepatotoxic side effects of dantrolene. Baclofen is not generally used as therapy for acute paravertebral muscle spasm.

Dantrolene

Dantrolene (Dantrium®) is a peripherally acting skeletal muscle relaxant that produces its effect by interfering with the release of calcium from the sarcoplasmic reticulum. It is used to decrease spasticity associated with upper motor neuron disorders and to treat malignant hyperthermia by reducing the hypermetabolic processes associated with this disorder. It has been associated with serious hepatoxicity. Dantrolene is not indicated for the treatment of other painful conditions.

Disclaimer

This drug information is for educational purposes only. It is not intended that this information covers all uses, directions, drug interactions, precautions, or adverse effects of your medication. This is only general information, and should not be relied on for any purpose. It should not be construed as containing specific instructions for any particular patient. We disclaim all responsibility for the accuracy and reliability of this information, and/or any consequences arising from the use of this information, including damage or adverse consequences to persons or property, however such damages or consequences arise. No warranty, either expressed or implied, is made in regards to this information.