Pharm

Cyclobenzaprine

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Cyclobenzaprine, Flexeril

See Also

Antispasmodic Skeletal Muscle Relaxant

Indications

Acute back or Neck Pain interfering with sleep despite Analgesics
1. Limit to short-course (<14 days)

Mechanism

Antispasmodic Skeletal Muscle Relaxant
Centrally acting cyclical Antidepressant with Sedative qualities
1. Tricyclic amine salt similar to Amitriptyline
Reduces Muscle hyperactivity and somatic motor activity
1. Mechanism may act at 5-H2 receptors, inhibiting descending serotonergic pathways in the cord

Dosing
Immediate Release

Start: 5 mg orally at bedtime (5 mg is as effective as 10 mg and with less sedation)
Maximum: 10 mg orally three times daily (primarily at bedtime for pain interfering with sleep)

Dosing
Extended Release

Start 15 mg orally daily
Maximum: 30 mg orally daily

Contraindications

Older patients
1. See Medications to Avoid in Older Adults
Seizure Disorder (if concurrently on Tramadol)
Glaucoma
Cardiac Arrhythmia
Congestive Heart Failure
Recent Myocardial Infarction

Efficacy

See Antispasmodic Skeletal Muscle Relaxant
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

See Antispasmodic Skeletal Muscle Relaxant for precautions
Common: Anticholinergic
1. Fatigue
2. Drowsiness
3. Dry Mouth (Xerostomia)
4. Urinary Retention
5. Increased Intraocular Pressure
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

References