Tizanidine
Tizanidine
Zanaflex
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Summary
Common uses
Spasticity in multiple sclerosis (FDA)0, Spasticity in spinal cord injury (FDA)0, Spasticity in cerebral palsy (FDA)0, Acute musculoskeletal pain (off-label)0
Pharmacy
Starting dose
2 mg PO every 6-8 hours; titrate by 2-4 mg per dose every 1-4 days; maximum single dose 16 mg, maximum daily dose 36 mg
Preparations
Tablets 2, 4 mg; capsules 2, 4, 6 mg (capsules and tablets are not bioequivalent: capsules slower with food; tablets faster on empty stomach)
US FDA Max
36 mg/day in three divided doses; single dose maximum 16 mg
Pharmacology
Routes
Oral
Onset
30-60 minutes
Duration
3-6 hours per dose
Half-life
2.5 hours (short, requires TID-QID dosing)[1]
Bioavailability
~40% (oral); food and formulation substantially alter the absorption profile[1]
Pregnancy
Limited human data.[citation needed]
Legal status
Purported mechanism
Centrally-acting α2-adrenergic receptor agonist closely related to clonidine, but with greater selectivity for spinal cord α2 receptors over peripheral α2, producing antispastic effect with somewhat less systemic hypotension and sedation than clonidine at equipotent muscle-relaxant doses. The mechanism reduces excitatory neurotransmitter release from spinal interneurons.0 CYP1A2 substrate with major interaction signal: fluvoxamine raises plasma exposure ~33-fold and ciprofloxacin ~10-fold, with severe hypotension reported; both combinations are contraindicated. Hepatotoxicity signal warrants baseline and periodic LFT monitoring with chronic use[1].
References
- ↑ 1.0 1.1 1.2 1.3 FDA Prescribing Information, Zanaflex (tizanidine hydrochloride), Acorda Therapeutics, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/020397s029,021447s011lbl.pdf