Flexeril (cyclobenzaprine hydrochloride) is a centrally-acting skeletal muscle relaxant indicated as an adjunct to rest and physical therapy for the relief of muscle spasm associated with acute, painful musculoskeletal conditions. It works by acting primarily within the central nervous system (CNS) at the brainstem level, reducing tonic somatic motor activity. While it does not directly relax skeletal muscles, its efficacy is believed to stem from its sedative properties. Improvement is often seen within the first few days of therapy, and it is intended for short-term use, typically not exceeding two or three weeks, due to insufficient evidence of longer-term effectiveness and a concomitant increase in the risk of adverse reactions.

Features

• Active Ingredient: Cyclobenzaprine hydrochloride
• Available Strengths: 5 mg and 10 mg oral tablets
• Mechanism of Action: Centrally-acting skeletal muscle relaxant; believed to primarily work through CNS depression at the brainstem level.
• Onset of Action: Symptomatic relief often begins within the first 24 to 72 hours of administration.
• Duration of Therapy: Recommended for short-term use (up to 2 or 3 weeks).
• Bioavailability: Well-absorbed following oral administration, but undergoes significant first-pass metabolism.
• Half-Life: Approximately 1-3 days for the parent drug and its metabolites.

Benefits

• Provides rapid relief from acute muscle spasm and associated local pain, facilitating a quicker return to normal activity.
• Acts as an effective adjunct to physical therapy and rest, enhancing the overall therapeutic regimen.
• Helps reduce muscle hypertonicity and stiffness, improving range of motion.
• May aid in breaking the cycle of pain-spasm-pain, promoting a more comfortable recovery period.
• Its centrally-acting mechanism provides targeted relief without direct peripheral muscle action, aligning with a neurocentric approach to spasm management.
• Short-term use profile helps minimize long-term systemic exposure and potential for dependency when used as directed.

Common use

Flexeril is commonly prescribed for the management of acute musculoskeletal conditions characterized by muscle spasm. This includes, but is not limited to, acute episodes of back pain, neck pain, torticollis, and muscle strain injuries resulting from trauma, overexertion, or sudden movement. It is used as part of a comprehensive treatment plan that should include rest, physical therapy, and other supportive measures. Its use is specifically for acute settings; it is not indicated for the treatment of spasticity associated with cerebral or spinal cord diseases, or in children.

Dosage and direction

The usual recommended dosage of Flexeril for most adults is 5 mg administered three times daily. Based on individual patient response and tolerability, the dosage may be increased to 10 mg three times daily. Dosing should be spaced as evenly as possible throughout the waking hours. Use of Flexeril for periods longer than two or three weeks is not recommended. The tablet should be swallowed whole with a full glass of water; it can be taken with or without food. Dosage adjustments are necessary for the elderly and for those with hepatic impairment, often initiating at the lower end of the dosing range. It is not recommended for use in pediatric patients.

Precautions

Flexeril has potent sedative properties; patients should be cautioned about performing activities requiring mental alertness, such as operating machinery or driving a motor vehicle, especially during the initial period of therapy or following a dosage increase. It may enhance the effects of alcohol and other CNS depressants. Use with caution in patients with mild hepatic impairment; it is not recommended in patients with moderate to severe hepatic impairment. Due to its structural similarity to tricyclic antidepressants (TCAs), it should be used with extreme caution in patients with a history of urinary retention, angle-closure glaucoma, increased intraocular pressure, or cardiovascular disorders. Abrupt cessation after prolonged use should be avoided.

Contraindications

Flexeril is contraindicated in patients hypersensitive to any component of the formulation. Concomitant use or within 14 days of discontinuation of monoamine oxidase inhibitors (MAOIs) is contraindicated due to the risk of hyperpyretic crisis, severe seizures, and death. It is also contraindicated in patients with hyperthyroidism, congestive heart failure, cardiac arrhythmias, conduction disturbances, or during the acute recovery phase following a myocardial infarction. Its use is contraindicated in patients with moderate to severe hepatic impairment.

Possible side effect

The most frequently reported adverse reactions are drowsiness, dry mouth, and dizziness. Other common side effects (≥3%) include fatigue, asthenia, nausea, dyspepsia, and constipation. These are often transient and dose-related. Less common but more serious side effects can include tachycardia, arrhythmias, syncope, seizures, hallucinations, and signs of an allergic reaction (e.g., rash, urticaria, swelling). Due to its tricyclic nature, it possesses anticholinergic side effects and can rarely cause serotonin syndrome, especially when used with other serotonergic drugs.

Drug interaction

Flexeril can have significant interactions. Concomitant use with other CNS depressants (e.g., alcohol, benzodiazepines, opioids, sedative hypnotics) can lead to additive CNS depression. It is absolutely contraindicated with MAOIs. Use with other anticholinergic drugs increases the risk of anticholinergic toxicity (e.g., severe dry mouth, urinary retention, hyperthermia). It may potentiate the effects of sympathomimetic amines. As it is metabolized by CYP1A2, CYP3A4, and to a lesser extent CYP2D6, inhibitors of these enzymes (e.g., fluvoxamine, ketoconazole) may increase cyclobenzaprine concentrations. It may interact with guanethidine and similar agents.

Missed dose

If a dose is missed, it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed one, as this increases the risk of adverse effects.

Overdose

Symptoms of overdose may include severe drowsiness, tachycardia, tremor, agitation, confusion, hallucinations, and cardiac arrhythmias. Severe overdose may lead to coma, convulsions, and cardiac arrest. Death has been reported with polypharmacy overdoses including cyclobenzaprine. Management is primarily supportive and symptomatic, including securing the airway and ensuring proper ventilation. Activated charcoal may be beneficial if administered early. Cardiac rhythm and vital signs should be monitored continuously. There is no specific antidote.

Storage

Store Flexeril tablets at room temperature, between 20°C to 25°C (68°F to 77°F), with excursions permitted between 15°C to 30°C (59°F to 86°F). Keep the medication in its original container, tightly closed, and out of reach of children and pets. Protect from light and moisture. Do not store in bathrooms or other damp places. Properly discard any unused medication after the course of therapy is complete or after the expiration date has passed.

Disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting any new treatment. Never disregard professional medical advice or delay in seeking it because of something you have read here. The information provided is not exhaustive and may not cover all possible uses, directions, precautions, interactions, or adverse effects.

Reviews

Clinical studies and post-marketing surveillance indicate that Flexeril is generally well-tolerated and effective for its approved indication of short-term relief of acute muscle spasm. In controlled clinical studies, Flexeril 10 mg demonstrated superior efficacy to placebo in relieving muscle spasm, local pain, and tenderness, and in improving range of motion. The most common reason for discontinuation in trials was drowsiness. Patient reviews often cite its effectiveness in breaking severe muscle spasms but frequently mention sedation and dry mouth as notable side effects. Its utility is widely recognized in acute care settings, though its use is appropriately limited by its side effect profile and short-term treatment recommendation.