What is the recommended dose of Flexeril (cyclobenzaprine) for a female patient with acute muscle spasm, considering her weight and potential medical history, including any history of liver or kidney disease?

Dosing Cyclobenzaprine (Flexeril) for Acute Muscle Spasm

For acute muscle spasm in a female patient, start cyclobenzaprine 5 mg three times daily, which can be increased to 10 mg three times daily based on response, with treatment duration limited to 2-3 weeks maximum. 1

Standard Dosing Protocol

The FDA-approved dosing is 5 mg three times daily as the initial dose for most patients, with the option to increase to 10 mg three times daily if needed. 1 Weight-based dosing is not required for cyclobenzaprine, as the standard dosing applies regardless of patient weight. 1

Dosing Rationale

• The 5 mg three times daily regimen produces significantly less sedation than 10 mg three times daily while maintaining comparable efficacy for muscle spasm relief. 2
• Clinical trials demonstrated that 5 mg three times daily was as effective as 10 mg three times daily, with onset of relief apparent within 3-4 doses. 2
• The 2.5 mg three times daily dose was not significantly more effective than placebo and should not be used. 2

Critical Prescribing Limitations

Cyclobenzaprine is indicated ONLY for acute muscle spasm associated with musculoskeletal conditions—NOT for muscle cramps. 3 For muscle cramps, baclofen is the preferred agent, starting at 10 mg/day with weekly increases of 10 mg/day up to 30 mg/day. 3

Treatment duration must not exceed 2-3 weeks, as there is no evidence supporting efficacy or safety beyond this period. 1

Important Safety Considerations

Contraindications and Drug Interactions

• Absolute contraindication: Do not combine with monoamine oxidase inhibitors due to risk of serotonin syndrome. 3, 4
• Hold cyclobenzaprine on the day of any surgical procedure due to potential interactions with anesthetics and sedatives. 5, 3

Common Adverse Effects

The most frequent side effects are dose-related and include: 3

• Drowsiness (most common)
• Dry mouth
• Dizziness
• Anticholinergic effects (constipation, urinary retention)

Somnolence occurs significantly less frequently with 5 mg dosing (0.8%) compared to 10 mg three times daily (7.3%). 6

Discontinuation Protocol

If cyclobenzaprine has been used for extended periods, taper over 2-3 weeks rather than stopping abruptly to prevent withdrawal symptoms (malaise, nausea, headache lasting 2-4 days). 5, 4

Alternative Formulation

An extended-release formulation (cyclobenzaprine ER 15-30 mg once daily) is available and provides comparable efficacy with potentially less daytime drowsiness, though the immediate-release formulation remains the standard. 7, 6

Clinical Efficacy Timeline

• Relief typically begins within 3-4 doses of the 5 mg regimen. 2
• Maximum benefit is generally achieved by day 4 of treatment. 7, 6
• Efficacy is independent of sedation—patients who do not experience somnolence still achieve meaningful symptom relief. 2