Pharm

Cyclobenzaprine

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Cyclobenzaprine, Flexeril, Tonmya

  • See Also
  1. Antispasmodic Skeletal Muscle Relaxant
  • Indications
  1. Acute back or Neck Pain interfering with sleep despite Analgesics
    1. Limit to short-course (<14 days)
  2. Fibromyalgia
    1. Mixed evidence in studies (NNT 8 for 30% pain reduction)
  • Mechanism
  1. Antispasmodic Skeletal Muscle Relaxant
  2. Centrally acting cyclical Antidepressant with Sedative qualities
    1. Tricyclic amine salt similar to Amitriptyline
  3. Reduces Muscle hyperactivity and somatic motor activity
    1. Mechanism may act at 5-H2 receptors, inhibiting descending serotonergic pathways in the cord
  • Medications
  1. Cyclobenzaprine Immediate Release Oral Tablets (Flexeril): 5 mg, 7.5 mg, 10 mg
  2. Cyclobenzaprine Extended Release Oral Capsules (Amrix XR): 15 mg, 30 mg
  3. Cyclobenzaprine sublingual tablets (Tonmya): 2.8 mg
    1. Released in 2025 for Fibromyalgia with no better efficacy and at a cost of $31/tablet
  • Dosing
  • Immediate Release
  1. Start: 5 mg orally at bedtime (5 mg is as effective as 10 mg and with less sedation)
  2. Maximum: 10 mg orally three times daily (primarily at bedtime for pain interfering with sleep)
  • Dosing
  • Extended Release
  1. Start 15 mg orally daily
  2. Maximum: 30 mg orally daily
  • Dosing
  • Sublingual Tablet
  1. Start 2.8 mg orally daily at bedtime
  2. Maximum: 5.6 mg (2 tablets)
  • Contraindications
  1. Older patients
    1. See Medications to Avoid in Older Adults
  2. Seizure Disorder (if concurrently on Tramadol)
  3. Glaucoma
  4. Cardiac Arrhythmia
  5. Congestive Heart Failure
  6. Recent Myocardial Infarction
  • Efficacy
  1. See Antispasmodic Skeletal Muscle Relaxant
  2. Poor evidence for benefit
    1. More effective than Placebo for first 4 days of Low Back Pain
    2. However, no significant functional or pain benefit at 1 week for Acute Low Back Pain (non-Traumatic, non-radicular)
  • Adverse Effects
  1. See Antispasmodic Skeletal Muscle Relaxant for precautions
  2. Common: Anticholinergic
    1. Fatigue
    2. Drowsiness
    3. Dry Mouth (Xerostomia)
    4. Urinary Retention
    5. Increased Intraocular Pressure
  3. Rare
    1. Arrhythmia
      1. Reflex Tachycardia
        1. Cyclobenzaprine may block alpha-1 Adrenergic Receptors resulting in vasodilation
      2. QRS Widening
        1. Fast-acting Sodium channel blockade (as with Amitriptyline)
    2. Seizure
      1. GABA Receptor inhibition may lower Seizure threshold
    3. Myocardial Infarction
    4. Serotonin Syndrome
      1. Risk when Cyclobenzaprine is combined with other serotonergic drugs
  • Resources
  1. Cyclobenzaprine IR (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=592871f6-0eb2-4624-9e10-bd8bf767c002
  2. Cyclobenzaprine XR (DailyMed)
    1. https://dailymed.nlm.nih.gov/dailymed/lookup.cfm?setid=ca74d27a-f7c6-462d-a913-1cfa061bd8f3
  • References
  1. (2/2026) Presc Insights, TRC healthcare
  2. Borenstein (2003) Clin Ther 25(4): 1056-73 [PubMed]
  3. Browning (2001) Arch Intern Med 161: 1613-20 [PubMed]
  4. Tofferi (2004) Arthritis Rheum 51:9-13 [PubMed]