Cyclobenzaprine

Cyclobenzaprine is a centrally acting skeletal muscle relaxant used to relieve muscle spasm associated with acute musculoskeletal conditions. It is available under brand names such as Flexeril, Amrix, and Fexmid. Therapy is typically short term, often two to three weeks.

Mechanism of action is primarily central. Cyclobenzaprine is chemically related to tricyclic antidepressants and exerts its effects mainly in the brainstem, where it reduces tonic motor activity and spasm. It does not act directly on muscle tissue.

Uses and limitations include relief of muscle spasm due to acute strain, sprain, or other musculoskeletal conditions. It is not intended for long-term treatment or for chronic spasticity from neurologic disease, and it has no disease-modifying effects.

Administration and formulations vary. Cyclobenzaprine is available as immediate-release tablets (commonly 5 mg or 10 mg) and extended-release formulations. Dosing is individualized per product labeling and clinician guidance; therapy is generally limited to short durations because of the potential for adverse effects and interactions with other central nervous system depressants.

Contraindications and precautions include concurrent use with monoamine oxidase inhibitors or use within 14 days of MAOI therapy. Caution is advised in older adults and in patients with cardiac conduction abnormalities, congestive heart failure, hyperthyroidism, glaucoma, or urinary retention due to anticholinergic effects. Alcohol and other central nervous system depressants should be avoided or minimized.

Adverse effects are typically mild and include drowsiness, dizziness, dry mouth, and fatigue. More serious but less common effects include arrhythmias, tachycardia, allergic reactions, and, rarely, confusion or blurred vision.