Flexeril (Cyclobenzaprine) Uses
Flexeril (cyclobenzaprine) is indicated as an adjunct to rest and physical therapy for relief of muscle spasm associated with acute, painful musculoskeletal conditions for short periods (up to two or three weeks). 1
Primary Indication and Mechanism
Cyclobenzaprine is a centrally acting skeletal muscle relaxant that works through:
- Inhibition of tonic somatic motor function
- Modulation of noradrenergic and serotonergic systems 2
- Non-competitive antagonism of histamine H1 receptors, which may contribute to its sedative effects 2
The medication is specifically designed to improve:
- Relief of muscle spasm
- Reduction of associated pain and tenderness
- Increased range of motion
- Decreased restriction in activities of daily living 1
Important Limitations
Cyclobenzaprine should NOT be used for:
- Long-term treatment (beyond 2-3 weeks) due to lack of evidence for prolonged effectiveness 1
- Treatment of spasticity associated with cerebral or spinal cord disease 1
- Children with cerebral palsy 1
Dosing Considerations
- Standard dosing: 5-10 mg three times daily 3
- Starting dose for elderly or those with mild hepatic impairment: 5 mg 3
- Lower dose regimen (5 mg TID) is as effective as 10 mg TID with fewer sedative effects 4
- Onset of relief typically occurs within 3-4 doses of the 5 mg regimen 4
Contraindications
Cyclobenzaprine is contraindicated in patients with:
- MAO inhibitor use (current or within 14 days of discontinuation) 3
- Acute recovery phase of myocardial infarction 3
- Heart block, conduction disturbances, or arrhythmias 3
- Hyperthyroidism 3
Common Adverse Effects
The most frequent side effects include:
- Drowsiness/sedation (dose-related)
- Anticholinergic effects:
- Dry mouth
- Constipation
- Urinary retention
- Hallucinations and confusion (less common) 3
- Dizziness 5
Clinical Evidence and Efficacy
Systematic reviews have found that skeletal muscle relaxants like cyclobenzaprine are:
- Moderately superior to placebo for short-term pain relief in acute low back pain 6
- Not proven superior to acetaminophen or NSAIDs for low back pain 5
- Potentially more effective when combined with NSAIDs (like naproxen) than NSAIDs alone 7
Important Clinical Considerations
Driving safety: Cyclobenzaprine significantly impairs driving ability compared to placebo; patients should be cautioned about operating machinery or driving 3
Drug interactions:
- Avoid combining with alcohol due to potentially fatal CNS depression
- Exercise caution with other CNS depressants
- Avoid co-prescribing with opioids or benzodiazepines when possible 3
Discontinuation:
- Tapering is recommended after prolonged use
- Withdrawal symptoms may include malaise, nausea, and headache lasting 2-4 days
- Consider gradual tapering over 2-3 weeks 3
Cyclobenzaprine remains one of the most heavily studied skeletal muscle relaxants and has demonstrated effectiveness for various acute musculoskeletal conditions, but should be used judiciously given its side effect profile and limited duration of recommended use.