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Amrix (cyclobenzaprine hydrochloride extended release)

Company: Cephalon
Approval Status: Approved February 2007
Treatment for: muscle spasm associated with acute, painful musculoskeletal conditions
Areas: Musculoskeletal; Neurology & Nervous System

| General Information | Clinical Results | Side Effects | Mechanism of Action | Literature References | Additional Information |


General Information

Amrix (cyclobenzaprine hydrochloride) is a once daily extended release skeletal muscle relaxant which relieves muscle spasm of local origin without interfering with muscle function. The exact mechanism of action is unknown. However, cyclobenzaprine hydrochloride is thought to act primarily at brain stem (and to a lesser extent at spinal cord level) to relieve skeletal muscle spasms of local origin without altering muscle function.

Amris is specifically indicated as an adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions.

Amrix is supplied as 15mg and 30mg capsules for oral administration. The recommended initial dose of the drug is one (1) 15 mg capsule taken once daily. Some patients may require up to 30 mg/day, given as one (1) 30 mg capsule taken once daily or as two (2) 15 mg capsules taken once daily. It is recommended that doses be taken at approximately the same time each day. Use of Amrix for periods longer than two or three weeks is not recommended.


Clinical Results

FDA Approval
The FDA approval of Amrix was based on the results of two identical double-blind, parallel-group, placebo-controlled studies: Study 1105 evaluated 30 mg of Amrix and Study 1106 studied 15 mg of Amrix both taken once daily for 14 days. The primary efficacy endpoint was the patient’s rating of medication helpfulness, measured at Day 4 and Day 14, between the two Amrix arms versus placebo. The primary endpoint was reached with signifcance for both Amrix arms. In addition, one of the two studies demonstrated significant differences between the Amrix 30 mg group and the placebo group in terms of patient-rated relief from local pain due to muscle spasm at Day 4 and Day 8, in subject-rated restriction of movement at Day 4 and Day 8, and in patient-rated global impression of change at Day 4, Day 8, and Day 14.


Side Effects

Adverse events associated with the use of Amrix may include, but are not limited to, the following:

  • Dry mouth
  • Dizziness
  • Fatigue
  • Somnolence
  • Headache
  • Nausea

Mechanism of Action

Amrix (cyclobenzaprine hydrochloride) is a once daily extended release skeletal muscle relaxant which relieves muscle spasm of local origin without interfering with muscle function. The exact mechanism of action is unknown. However, cyclobenzaprine hydrochloride is thought to act primarily at brain stem (and to a lesser extent at spinal cord level) to relieve skeletal muscle spasms of local origin without altering muscle function.


Literature References

Malanga GA, Ruoff GE, Weil AJ, Altman CA, Xie F, Borenstein DG Cyclobenzaprine ER for muscle spasm associated with low back and neck pain: two randomized, double-blind, placebo-controlled studies of identical design. Current Medical Research and Opinion< 2009 May;25(5):1179-96

Darwish M, Hellriegel ET, Xie F Single-dose pharmacokinetics of once-daily cyclobenzaprine extended release 30 mg versus cyclobenzaprine immediate release 10 mg three times daily in healthy young adults : a randomized, open-label, two-period crossover, single-centre study. Clinical Drug Investigation 2008;28(12):793-801


Additional Information

For additional information regarding Amrix or muscle spasms, please visit the Amrix web page.


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Amrix Drug Information

The Amrix drug information shown above is licensed from Thomson CenterWatch. The information provided here is for general educational purposes only and does not constitute medical or pharmaceutical advice which should be sought from qualified medical and pharmaceutical advisers.





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