What is the recommended cyclobenzaprine dosing for acute muscle spasm in a healthy adult, including starting dose, extended‑release regimen, maximum duration, and how should the dose be adjusted in patients ≥65 years or with moderate hepatic impairment, as well as the contraindications and alternative muscle relaxants?

Cyclobenzaprine Dosing for Acute Muscle Spasm

For healthy adults under 65 years with acute muscle spasm, start cyclobenzaprine immediate-release 5 mg three times daily, which is as effective as higher doses but better tolerated; alternatively, use extended-release 15 mg once daily for 7–14 days maximum. 1, 2

Standard Dosing in Healthy Adults

Immediate-Release Formulation

• Starting dose: 5 mg three times daily (TID) orally 1
• Alternative dose: 10 mg TID if 5 mg is insufficient, though this increases sedation risk 2
• Maximum duration: 2 weeks 3
• The 5 mg TID regimen demonstrated equivalent efficacy to combination therapy with ibuprofen in a randomized trial of 867 patients, with 93% reporting at least mild improvement after 7 days 1

Extended-Release Formulation

• Starting dose: 15 mg once daily 2
• Higher dose option: 30 mg once daily if needed 2
• Maximum duration: 14 days 2
• Extended-release 30 mg provides approximately twice the systemic exposure as 15 mg, with a single daily peak versus three peaks with immediate-release 4
• Both CER 15 mg and 30 mg showed significantly greater improvements in medication helpfulness versus placebo at day 4 (p < 0.025), with lower somnolence rates (0.8% and 1.6% respectively) compared to immediate-release 10 mg TID (7.3%) 2

Dose Adjustments for Special Populations

Elderly Patients (≥65 Years)

• Avoid cyclobenzaprine entirely in patients ≥65 years 3
• The American Geriatrics Society Beers Criteria lists cyclobenzaprine as potentially inappropriate due to anticholinergic effects, sedation, and increased fall risk 5
• Systemic exposure to cyclobenzaprine is increased in elderly subjects, raising toxicity risk 4
• Preferred alternative: Baclofen starting at 5 mg three times daily, titrated weekly to maximum 30–40 mg/day 3

Moderate Hepatic Impairment

• Contraindicated—do not use cyclobenzaprine 3
• Cyclobenzaprine is structurally related to tricyclic antidepressants and undergoes extensive hepatic metabolism 5
• Alternative: Consider baclofen with careful monitoring, as it has documented efficacy for muscle spasm 3

Contraindications

Absolute Contraindications

• Concomitant use with monoamine oxidase inhibitors (risk of serotonin syndrome) 6
• Moderate to severe hepatic impairment 3
• Acute recovery phase of myocardial infarction 5
• Hyperthyroidism, heart block, arrhythmias, or congestive heart failure 5

Relative Contraindications (Use Extreme Caution)

• Age ≥65 years (Beers Criteria potentially inappropriate medication) 3, 5
• Frail patients with mobility deficits, weight loss, weakness, or cognitive impairment 3
• Patients taking other anticholinergic medications 3
• Scheduled surgery (hold on day of procedure due to interactions with anesthetics) 6, 5

Alternative Muscle Relaxants

Preferred Alternative: Baclofen

• Indication: True muscle spasm or spasticity, particularly with CNS injury or neuromuscular disorders 3
• Starting dose: 5 mg three times daily 3
• Titration: Increase weekly by small increments 3
• Maximum dose: 30–40 mg/day (elderly rarely tolerate higher doses) 3
• Critical warning: Never discontinue abruptly—requires slow taper to avoid withdrawal symptoms including delirium, seizures, and CNS irritability 3

Second-Line Alternative: Tizanidine

• Starting dose: 2 mg up to three times daily 3
• Duration: ≤2 weeks for acute muscle spasm 3
• Provided moderate short-term pain relief (2–4 days) in eight randomized trials of acute low-back pain 3
• Cautions: Monitor for orthostatic hypotension, sedation, and drug-drug interactions; use caution in renal impairment 3
• Note: Some guidelines recommend avoiding tizanidine in older adults due to significant sedation and hypotension 3

Agents to Avoid

• Carisoprodol: Controlled substance with abuse potential; removed from European market 3
• Methocarbamol: Elimination significantly impaired in liver and kidney disease 3
• Metaxalone: Contraindicated in significant hepatic or renal dysfunction 3
• Orphenadrine: Strong anticholinergic properties causing confusion, urinary retention, cardiovascular instability 3

Common Pitfalls and Caveats

Anticholinergic Burden

• Common adverse effects include drowsiness, dry mouth, dizziness, constipation, and urinary retention 6
• Avoid combining with other anticholinergic medications 3
• Patients should be counseled to monitor for these effects 5

Discontinuation After Prolonged Use

• Gradual taper over 2–3 weeks is required after long-term use to prevent withdrawal symptoms (malaise, nausea, headache) 5
• Do not abruptly discontinue 5

Lack of Efficacy in Chronic Pain

• Cyclobenzaprine has no evidence of efficacy in chronic pain and should not be used for this indication 6
• It does not directly relax skeletal muscle 6
• Most muscle relaxants have nonspecific effects and should only be prescribed when true muscle spasm is suspected 3

Non-Pharmacological Approaches First

• Consider topical analgesics (lidocaine or diclofenac gels) for focal musculoskeletal pain, which provide relief with fewer systemic side effects 3
• Scheduled acetaminophen may be effective for mild to moderate musculoskeletal pain 3