AMRIX® (Cyclobenzaprine Hydrochloride Extended-Release Capsules) is a skeletal muscle relaxant which relieves muscle spasm of local origin without interfering with muscle function. The active ingredient in AMRIX extended-release capsules is cyclobenzaprine hydrochloride, USP.
AMRIX is indicated as an adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions. Improvement is manifested by relief of muscle spasm and its associated signs and symptoms, namely, pain, tenderness, and limitation of motion.
AMRIX 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 and because muscle spasm associated with acute, painful musculoskeletal conditions is generally of short duration and specific therapy for longer periods is seldom warranted.
AMRIX has not been found effective in the treatment of spasticity associated with cerebral or spinal cord disease or in children with cerebral palsy.
Media Articles Related to Amrix (Cyclobenzaprine)
Muscle Cramps (Charley Horse) and Muscle Spasms: Symptoms, Causes, and Treatments
Source: MedicineNet Muscle Cramps Specialty [2016.06.24]
Title: Muscle Cramps (Charley Horse) and Muscle Spasms: Symptoms, Causes, and Treatments
Created: 6/8/2015 12:00:00 AM
Last Editorial Review: 6/24/2016 12:00:00 AM
Source: MedicineNet Claudication Specialty [2016.04.21]
Title: Muscle Spasms
Category: Diseases and Conditions
Created: 6/16/2009 12:00:00 AM
Last Editorial Review: 4/21/2016 12:00:00 AM
Published Studies Related to Amrix (Cyclobenzaprine)
Evaluation of the muscle relaxant cyclobenzaprine after third-molar extraction. [2011.10]
BACKGROUND: Pain, swelling and trismus are undesirable effects of extraction of impacted mandibular third molars. The authors conducted a study to evaluate the effectiveness of the muscle relaxant cyclobenzaprine when used as a supplement to cryotherapeutic, antibiotic and steroidal anti-inflammatory treatment with the aim of reducing undesirable consequences after third-molar extraction... CONCLUSIONS: The results of this trial indicate that the influence of cyclobenzaprine over pain, swelling and trismus does not justify prescribing additional medication for patients undergoing third-molar extraction. CLINICAL IMPLICATIONS: The muscle relaxant cyclobenzaprine was ineffective in reducing pain, swelling and trismus after third-molar extraction.
Steady-state pharmacokinetics of once-daily cyclobenzaprine extended release: a randomized, double-blind, 2-period crossover study in healthy volunteers. [2011.06]
BACKGROUND: The single-dose pharmacokinetic profile of cyclobenzaprine extended-release (CER) has been previously characterized and compared with the pharmacokinetics of cyclobenzaprine immediate-release (CIR) administered 3 times daily for 3 doses. OBJECTIVE: The objective of this study was to characterize the multiple-dose pharmacokinetic properties of once-daily CER 30 mg and CIR 10 mg TID formulations in healthy volunteers... CONCLUSIONS: Once-daily CER 30 mg delivered sustained plasma cyclobenzaprine levels over 24 hours at steady state. Owing to a protocol violation, steady-state pharmacokinetic properties for CIR could not be assessed. Copyright (c) 2011 Elsevier HS Journals, Inc. All rights reserved.
Evaluation of the muscle relaxant cyclobenzaprine after third-molar extraction. 
aim of reducing undesirable consequences after third-molar extraction... CONCLUSIONS: The results of this trial indicate that the influence of
Steady-state pharmacokinetics of once-daily cyclobenzaprine extended release: a
randomized, double-blind, 2-period crossover study in healthy volunteers. 
in healthy volunteers... CONCLUSIONS: Once-daily CER 30 mg delivered sustained plasma cyclobenzaprine
Efficacy and tolerability of cyclobenzaprine extended release for acute muscle spasm: a pooled analysis. [2010.07]
OBJECTIVE: To assess the efficacy and tolerability of once-daily cyclobenzaprine extended release (CER) 15 and 30 mg in relieving acute muscle spasm... CONCLUSION: Once-daily CER was effective in relieving acute muscle spasm based on patient's rating of medication helpfulness at day 4 and was generally well tolerated with a low rate of reported somnolence.
Clinical Trials Related to Amrix (Cyclobenzaprine)
Cyclobenzaprine Extended Release (ER) for Fibromyalgia [Recruiting]
Amrix (Cyclobenzaprine hydrochloride Extended release capsules) is approved by the FDA as a
muscle relaxant, indicated for the treatment of muscle spasm associated with acute, painful
musculoskeletal conditions. Cyclobenzaprine ER (Amrix TM) has a distinct pharmacokinetic
profile providing early systemic exposure and consistent plasma concentration over several
hours. Overall, a single dose of Amrix 30 mg is similar to that of cyclobenzaprine immediate
release 10 mg three times daily. This ER formula should improve compliance, with similar
efficacy and possibly less side effects as is often the case with slower release
There are clinical studies showing that cyclobenzaprine can alleviate pain secondary to
Fibromyalgia induced muscle tone. This multi-layered evidence base suggests that
cyclobenzaprine may be able to alleviate pain in fibromyalgia. Theoretically in
fibromyalgia, pain is interpreted centrally and possibly occurs due to said muscle spasm .
Cyclobenzaprine may relieve this pain, thus allowing patients to function better during the
day and sleep better at night. Cyclobenzaprine has tricyclic antidepressant structure which
may also allow pain signal dampening in the spinal cord as well, similar to amitriptyline
which is used off-label for neuropathic pain as well.
Fibromyalgia (FM) is an illness that may involve medical, rheumatologic, autoimmune, sleep,
endocrine and psychiatric pathology. It is a syndrome of recurrent pain at trigger points.
Greater than 90% of these patients will report fatigue as a key symptom as well. There are
several investigation lines into the treatment of FM induced pain. Exercise, behavioral
therapy, amitryptiline, duloxetine, tramadol, sodium oxybate, pregabalin all have randomized
trials and almost all focus on pain. There are very few studies evaluating cyclobenzaprine
and none studying to Cyclobenzaprine ER formulation. None evaluate pain reduction, sleep
and fatigue improvement.
Cyclobenzaprine is a drug with minimal adverse effects (dry mouth, dizziness, fatigue,
constipation, somnolence, nausea, and dyspepsia). It may have a safer tolerability profile
than some of the FM medications noted above. As cyclobenzaprine is often studied and often
added as an augmentation agent to patients' regimens who suffer from acute painful
musculoskeletal conditions, the authors feel that cyclobenzaprine would also be effective in
this population. The authors wish to conduct a study to determine if cyclobenzaprine ER is
safe and tolerable in the treatment of FM induced pain, and secondary fatigue and insomnia.
This initial study may allow for continued regulatory studies with this product in FM
subjects. The authors propose a double-blind placebo controlled study to determine if
cyclobenzaprine ER is safe and effective in reversing FM induced pain, and secondary fatigue
Pilot Study of Cyclobenzaprine for Treatment of Sleep Disturbance in Aromatase Inhibitor-treated Breast Cancer Patients [Terminated]
Many women with breast cancer who are treated with aromatase inhibitor medications develop
difficulty sleeping and fatigue during treatment. Some examples of aromatase inhibitor
medications include anastrozole (Arimidex), exemestane (Aromasin), and letrozole (Femara).
Frequently, sleeping pills do not work very well to improve sleep. Cyclobenzaprine
(Flexeril) is a medication that was originally developed to treat muscle spasms. It may also
improve sleep in patients with chronic pain disorders, such as fibromyalgia. In this study
we are testing to see if cyclobenzaprine at bedtime will help improve sleep in women treated
with aromatase inhibitors.
Comparative Bioavailability of Sublingual TNX-102, Oral and Intravenous Cyclobenzaprine in Healthy Adults [Completed]
Very low dose (VLD) cyclobenzaprine at bedtime has shown promise as a treatment for
fibromyalgia, but the chemistry of cyclobenzaprine requires new formulation technology for
bedtime use. The present trial is designed to assess the safety and tolerability of
sublingual TNX-102 2. 4 mg (a new formulation of cyclobenzaprine designed to result in
increased dosage precision and decreased potential for morning grogginess) at pH 3. 5 and 7. 1
and to compare the bio-availability of sublingual TNX-102 2. 4 mg at pH 3. 5 and 7. 1 and
cyclobenzaprine (5 mg tablets, or 2. 4 mg iv).
Comparison of Ibuprofen, Cyclobenzaprine, or Both for Acute Cervical Strain: A Randomized Clinical Trial [Completed]
The purpose of this study is to see whether the combination of a muscle relaxant and
anti-inflammatory drug is more effective at relieving pain in patients with neck strains or
whiplash than either of the two medications alone.
Efficacy and Safety of Cyclobenzaprine Hydrochloride Extended Release for the Treatment of Chronic Migraine [Terminated]
The primary objective of the study is to evaluate the effectiveness and safety of
cyclobenzaprine hydrochloride extended release (Amrix 15mg/day) for the prophylaxis of
chronic migraine compared to a placebo medication. A second objective, is to find out
whether there is an improvement in quality of sleep and self-reported depression in patients
taking Amrix 15mg daily. The hypothesis is that the number of migraine days per month of
patients treated with Amrix 15mg daily will be significantly lower than those patients
treated with placebo.
Page last updated: 2016-06-24