Drug Groups

approved

Description

Cyclobenzaprine is a skeletal muscle relaxant and a central nervous system (CNS) depressant. Cyclobenzaprine acts on the locus coeruleus where it results in increased norepinephrine release, potentially through the gamma fibers which innervate and inhibit the alpha motor neurons in the ventral horn of the spinal cord. It is structurally similar to Amitriptyline, differing by only one double bond.

Indication

For use as an adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions.

Pharmacology

Cyclobenzaprine, closely related to the antidepressant amitriptyline, is used as a skeletal muscle relaxant to reduce pain and tenderness and improve mobility. Unlike dantrolene, cyclobenzaprine cannot be used to treat muscle spasm secondary to cerebral or spinal cord disease.

Toxicity

Oral mouse and rat LD₅₀ are 338 mg/kg and 425 mg/kg respectively. Signs of overdose include agitation, coma, confusion, congestive heart failure, convulsions, dilated pupils, disturbed concentration, drowsiness, hallucinations, high or low temperature, increased heartbeats, irregular heart rhythms, muscle stiffness, overactive reflexes, severe low blood pressure, stupor, and vomiting.

Affected Organisms

Biotransformation

Extensively metabolized (gastrointestinal and hepatic).

Absorption

Slowly but well absorbed after oral administration

Half Life

18 hours (range 8-37 hours)

Protein Binding

Very high (93%)

Elimination

Cyclobenzaprine is extensively metabolized, and is excreted primarily as glucuronides via the kidney.

Clearance

* 0.7 L/min

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