Flexeril (Cyclobenzaprine) Dosing for Adults
The recommended starting dose of cyclobenzaprine for most adult patients is 5 mg three times daily, which can be increased to 10 mg three times daily based on individual response, with treatment duration limited to 2-3 weeks. 1
Standard Dosing Regimen
- Initial dose: 5 mg orally three times daily 1
- Maximum dose: 10 mg orally three times daily if the 5 mg dose provides insufficient relief 1
- Treatment duration: 2-3 weeks maximum for acute musculoskeletal conditions 1
The FDA-approved labeling explicitly states these parameters for managing acute, painful musculoskeletal conditions 1. This conservative starting approach minimizes the risk of sedation and other anticholinergic side effects while maintaining therapeutic efficacy.
Evidence Supporting Lower-Dose Efficacy
The 5 mg three times daily regimen is as effective as 10 mg three times daily but causes significantly less sedation. 2 In two large randomized controlled trials involving 1,405 patients with acute muscle spasm:
- Both 5 mg and 10 mg doses were significantly superior to placebo on all primary efficacy measures (P ≤ 0.001) 2
- The 5 mg dose produced meaningful relief within 3-4 doses 2
- Somnolence rates were dose-dependent and lower with 5 mg compared to 10 mg 2
- Efficacy was independent of sedation, as demonstrated in subgroup analysis of patients without somnolence 2
A meta-analysis of back pain treatment found that cyclobenzaprine produces an odds ratio of 4.7 (95% CI: 2.7-8.1) for symptom improvement compared to placebo, with the greatest effect occurring in the first 4 days of treatment 3. This supports the recommendation for short-course therapy.
Special Population Adjustments
Elderly Patients
Reduce dosing frequency in elderly patients due to altered pharmacokinetics and increased risk of anticholinergic effects 1. While specific dose reductions aren't mandated by the FDA label, less frequent dosing (e.g., twice daily instead of three times daily) should be considered 1.
Pharmacokinetic studies in patients aged 65-75 years demonstrate similar systemic exposure to younger adults, but the elderly experience more pronounced cholinergic adverse effects 4.
Hepatic Impairment
Use less frequent dosing in patients with hepatic impairment 1. The FDA label specifically recommends this precaution, though it does not provide exact dosing parameters 1.
Extended-Release Formulation
An extended-release formulation (15 mg or 30 mg once daily) is available and provides:
- Similar efficacy to immediate-release formulation 5
- Significantly lower somnolence rates: 0.8% with 15 mg ER and 1.6% with 30 mg ER versus 7.3% with immediate-release 10 mg three times daily (P < 0.05) 5
- Median time to relief of 5-6 days versus 8 days for placebo 5
Common Pitfalls to Avoid
- Do not prescribe beyond 2-3 weeks: Efficacy declines after the first week, and prolonged use increases adverse effects without additional benefit 1, 3
- Do not start with 10 mg in all patients: The 5 mg dose is equally effective with better tolerability 2
- Warn patients about sedation: Drowsiness occurs in over 30% of patients and is mediated by potent non-competitive antagonism of central histamine H1 receptors 6
- Avoid in elderly without dose adjustment: Standard dosing may cause excessive sedation and anticholinergic effects 1, 4
Most Common Adverse Effects
The most frequently reported adverse effects are dose-related 2:
- Somnolence (most common)
- Dry mouth
- Dizziness
- Constipation
- Headache
These effects are mediated through cyclobenzaprine's high-affinity, non-competitive antagonism of histamine H1 receptors, explaining the significant sedation profile 6.