THERAPEUTICS

Brands

• Flexeril, Fexmid, Amrix, Apo-Cyclobenzaprine

Generic?

• Yes

Class

• Muscle relaxant

Commonly Prescribed for

(FDA approved in bold)

• Muscle spasm

• Neck pain/lower back pain

• Myofascial pain

• Fibromyalgia

How the Drug Works

• A tricyclic compound structurally similar to amitriptyline. It blocks serotonin and norepinephrine reuptake pumps and has anticholinergic effects. Acts on locus coeruleus and via gamma fibers to inhibit the alpha motor neurons in the ventral horn of the spinal cord, hence decreased muscle tone. Reduces tonic somatic motor activity

How Long Until It Works

• Pain: May work within hours but maximal effect occurs in 4–14 days

If It Works

• Titrate to most effective tolerated dose

If It Doesn't Work

• Increase to highest tolerated dose. If ineffective, consider alternative medications or other modalities

Best Augmenting Combos for Partial Response or Treatment-Resistance

• Use other centrally acting muscle relaxants with caution due to potential additive CNS depressant effect

• Combine with non-pharmacological treatments such as exercise/physical therapy, massage, heat/ice, or acupuncture

Tests

• Consider checking ECG for QTc prolongation at baseline and when increasing dose

ADVERSE EFFECTS (AEs)

How the Drug Causes AEs

• Anticholinergic and antihistaminic properties are causes of most common AEs

Notable AEs

• Dry mouth, dizziness, fatigue, constipation, weakness, sweating, and nausea are most common. Somnolence is more common with the intermediate-acting form

Life-Threatening or Dangerous AEs

• Orthostatic hypotension, tachycardia, QTc prolongation, and rarely death

• Increased intraocular pressure

• Paralytic ileus, hyperthermia

• Rare activation of mania or suicidal ideation

• Rare worsening of existing seizure disorders

• Serotonin syndrome

Weight Gain

• Not unusual

Sedation

• Common

What to Do About AEs

• For somnolence or fatigue, change to oncedaily formulation or decrease dose. For any serious AEs, discontinue

Best Augmenting Agents to Reduce AEs

• Most AEs cannot be reduced by use of augmenting agent