Dosing and uses of Zanaflex (tizanidine)
Adult dosage forms and strengths
tablet
- 2mg
- 4mg
capsule
- 2mg
- 4mg
- 6mg
Muscle Spasticity
Spasticity associated with multiple sclerosis and spinal cord injury
Initial: 2 mg PO q6-8hr PRN; no more than 3 doses q24hr
Maintenance: Titrate in 2-4 mg/day increments to optimum effect with minimum 1-4 days between dose increments
Not to exceed 36 mg/day; single doses >16 mg not studied
To discontinue taper gradually; decrease by 2-4 mg daily
Dosing Modifications
Renal impairment
- CrCl <25 mL/min: Use caution; clearance reduced >50%
- CrCl >25 mL/min: Not studied; use caution
Hepatic impairment
- Close monitoring of ADRs (eg, hypotension); avoid in severe impairment
Pediatric dosage forms and strengths
Not recommended
Zanaflex (tizanidine) adverse (side) effects
>10%
Dry mouth (46-50%)
Somnolence (46-50%)
Dizziness (16-20%)
Asthenia (10-45%)
1-10%
Blurred vision (3%)
Constipation (4%)
Infection (6%)
LFT abnormalities (3-5%)
Speech disorder (3%)
Vomiting (3%)
Urinary frequency (3%)
UTI (10%)
Frequency not defined
Asthenia
Bradycardia
Hypotension
Orthostatic hypotension
Syncope (rare)
Warnings
Contraindications
Hypersensitivity
Concomitant ciprofloxacin or fluvoxamine, or other potent CYP1A2 inhibitors
Cautions
Potential for hypotension
Caution in renal/hepatic impairment
Women on oral contraceptives
Hepatotoxicity may occur; monitor aminotransferases prior to and during use
Sedation may occur (dose related); may potentiate effect of sedative drugs or ethanoL
Visual hallucinations may occur
CYP1A2 inducers may decrease levels
Rebound hypertension, tachycardia, and hypertonia reported upon abrupt discontinuation; decrease doses slowly in patients taking concomitant narcotics or high doses (20-28 mg/day) for prolonged periods
Pregnancy and lactation
Pregnancy category: C
Lactation: May be excreted in breast milk due to lipophilic nature; use caution
Pregnancy categories
A: Generally acceptable. Controlled studies in pregnant women show no evidence of fetal risk.
B: May be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.
C: Use with caution if benefits outweigh risks. Animal studies show risk and human studies not available or neither animal nor human studies done.
D: Use in LIFE-THREATENING emergencies when no safer drug available. Positive evidence of human fetal risk.
X: Do not use in pregnancy. Risks involved outweigh potential benefits. Safer alternatives exist.
NA: Information not available.
Pharmacology of Zanaflex (tizanidine)
Mechanism of action
Alpha-2 adrenergic receptor agonist structurally related to clonidine; increases presynaptic inhibition of motor neurons
Absorption
Bioavailability: 40%
Peak serum time: 1-4 hr
Distribution
Protein bound: 30%
Vd: 2.4 L/kg
Metabolism
Extensively metabolized in the liver
Elimination
Half-life: 2.5 hr
Excretion: Feces (20%); urine (60%)
