Tizanidine Dosing
Start tizanidine at 2 mg orally at bedtime, then increase by 2-4 mg increments every 3-7 days as tolerated, up to a maximum of 8 mg three times daily (24 mg/day total), with mandatory dose reductions required for hepatic impairment, renal impairment, and patients taking CYP1A2 inhibitors including oral contraceptives. 1, 2
Standard Adult Dosing
- Initial dose: 2 mg orally at night 1, 3
- Titration: If well tolerated, increase by 2-4 mg increments every 3-7 days 1, 4
- Maintenance dose: Most patients respond to 12-24 mg/day divided into 2-3 doses 5, 6
- Maximum dose: 8 mg every 8 hours (24 mg/day total) 1
- Therapeutic range: The effective dose ranges from 6-36 mg/day, though doses above 24 mg/day have limited safety data 2, 7
The drug exhibits high interpatient variability in plasma concentrations, necessitating individualized titration over 2-4 weeks to achieve optimal muscle tone reduction while minimizing adverse effects 6, 4.
Hepatic Impairment
Tizanidine is contraindicated or should be used with extreme caution in hepatic impairment. 2
- Approximately 5% of patients develop liver enzyme elevations >3 times upper limit of normal 2
- Three fatal cases of hepatic failure have been reported in postmarketing surveillance 2
- Monitoring requirement: Obtain baseline liver function tests, then repeat at 1,3, and 6 months, and periodically thereafter 2
- If hepatic impairment is present, use only if absolutely necessary with reduced doses and close monitoring 2
Renal Impairment
For creatinine clearance <25 mL/min, reduce individual doses rather than dosing frequency, and monitor closely for adverse effects. 2
- Clearance is reduced by >50% in patients with creatinine clearance <25 mL/min 2
- During titration, reduce individual doses rather than extending dosing intervals 2
- If higher doses are required, increase the individual dose amount, not the frequency 2
- Key monitoring parameters: Watch for dry mouth, somnolence, asthenia, and dizziness as indicators of potential overdose 2
A case report documented severe liver, renal, and cardiovascular failure in a child receiving 1.6 mg/kg/day (approximately 10-fold higher than typical dosing), emphasizing the narrow therapeutic index 8.
Elderly Patients
Elderly patients require dose reduction due to decreased renal function and increased sensitivity to adverse effects. 9
- Start at 2 mg once daily at bedtime 3
- Titrate more slowly than in younger adults 3
- Elderly patients clear tizanidine four times slower than younger subjects 2
- Adverse effects of concern: A systematic review found 29.2% incidence of falls with tizanidine in community-dwelling adults >50 years 9
- Increased risk of bradycardia, hypotension, drowsiness, and encephalopathy 9
Critical Drug Interactions Requiring Dose Adjustment
Concomitant use of CYP1A2 inhibitors is contraindicated or requires substantial dose reduction. 2, 10
Oral Contraceptives
- Reduce tizanidine clearance by approximately 50% 2
- During titration, reduce individual doses 2
- Monitor closely for increased sedation and hypotension 2
Other CYP1A2 Inhibitors
- Contraindicated: Fluvoxamine, ciprofloxacin 2
- Severe hypotension and prolonged sedation can occur with concurrent use 10
Methadone
- Increased risk of QTc prolongation when used together 1
- Avoid combination or use with extreme caution and ECG monitoring 1
Food Effects
Food increases tizanidine absorption by approximately 30% and delays time to peak concentration by 25 minutes. 2
- Taking with food increases Cmax by 30% and extends Tmax from 1 hour to 1 hour 25 minutes 2
- Patients should be consistent in taking doses either with or without food to maintain stable plasma levels 2
Common Pitfalls and Safety Considerations
- Hypotension: Two-thirds of patients receiving 8 mg experience 20% reduction in blood pressure within 1-3 hours 2
- Sedation: 48% of patients report sedation; 92% report drowsiness at 16 mg dose 2
- Withdrawal: Do not discontinue abruptly after prolonged use; taper slowly to avoid rebound hypertension and tachycardia 2
- Alcohol: Increases tizanidine AUC by 20% and Cmax by 15%, with additive CNS depression 2