What is the recommended dosing of Flexeril (cyclobenzaprine) in adults, and how should it be adjusted for elderly patients or those with hepatic impairment?

Cyclobenzaprine (Flexeril) Dosing

Standard Adult Dosing

For most adults, cyclobenzaprine should be dosed at 5 mg three times daily, with the option to increase to 10 mg three times daily based on individual response. 1

• The 5 mg three times daily regimen is as effective as 10 mg three times daily for acute muscle spasm, but produces significantly less sedation 2
• If inadequate relief occurs with 5 mg, the dose may be increased to 10 mg three times daily 1
• Treatment duration should be limited to 2–3 weeks maximum, as efficacy beyond this period has not been established 1
• Onset of relief typically occurs within 3–4 doses of the 5 mg regimen 2

Elderly Patients

Cyclobenzaprine should be avoided in elderly patients whenever possible due to high risk of CNS adverse effects, sedation, falls, and anticholinergic toxicity. 3

• The American Geriatrics Society 2019 Beers Criteria explicitly recommends avoiding cyclobenzaprine in older adults due to poor risk-benefit ratio 3
• If use is unavoidable in elderly patients, less frequent dosing should be strongly considered 1
• Elderly patients (aged 65–75 years) demonstrate similar systemic exposure to cyclobenzaprine as younger adults, but may experience more pronounced adverse effects 4

Hepatic Impairment

Patients with hepatic dysfunction require reduced dosing frequency and lower starting doses. 1

• Less frequent dosing is mandatory for hepatically impaired patients 1
• Start at the lower end of the dosing range and titrate cautiously 1

Extended-Release Formulation (if applicable)

• Cyclobenzaprine extended-release (CER) 30 mg once daily provides comparable systemic exposure to immediate-release 10 mg three times daily 5
• CER 15 mg once daily provides approximately half the exposure of the 30 mg dose 6
• CER exhibits a single daily peak (median t_max ~6–8 hours) versus three peaks with immediate-release formulation 5, 4
• CER 15 mg and 30 mg demonstrate significantly less daytime drowsiness and somnolence (0.8% and 1.6%, respectively) compared to immediate-release 10 mg three times daily (7.3%) 7

Key Safety Considerations

• Somnolence and dry mouth are the most common adverse effects and are dose-related 2
• Combining cyclobenzaprine with other CNS depressants requires careful consideration of additive sedation risk 3
• The 5 mg dose produces meaningful efficacy independent of sedation, as demonstrated in subanalysis of patients who did not report somnolence 2
• Systemic exposure increases in the presence of food and in elderly subjects 6

Common Pitfalls to Avoid

• Do not prescribe cyclobenzaprine to elderly patients without compelling justification, as safer alternatives exist 3
• Do not continue treatment beyond 2–3 weeks, as prolonged use is not supported by evidence 1
• Do not start with 10 mg three times daily when 5 mg three times daily provides equivalent efficacy with better tolerability 2