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Tizanidine: Wikis


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Systematic (IUPAC) name
CAS number 51322-75-9
ATC code M03BX02
PubChem 5487
DrugBank APRD00128
ChemSpider 5287
Chemical data
Formula C 9H8ClN5S 
Mol. mass 253.712
SMILES eMolecules & PubChem
Synonyms 4-chloro-N-(4,5-dihydro-1H-imidazol-2-yl)-8-thia-7,9-diazabicyclo[4.3.0]nona-2,4,6,9-tetraen-5-amine
Pharmacokinetic data
Bioavailability  ?
Protein binding 30%
Metabolism CYP 1A2
Half life 2.54 hours
Excretion  ?
Therapeutic considerations
Pregnancy cat.  ?
Legal status Rx-Only, Unscheduled
Routes Oral, Intranasal, Injection
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Tizanidine (brandnames Zanaflex, Sirdalud) is a drug that is used as a muscle relaxant. It is a centrally acting α-2 adrenergic agonist. It is used to treat the spasms, cramping, and tightness of muscles caused by medical problems such as multiple sclerosis, spastic diplegia, back pain, or certain other injuries to the spine or central nervous system. It is also prescribed off-label for migraine headaches, as a sleep aid, and as an anticonvulsant. It is also prescribed for some symptoms of fibromyalgia[1].

Tizanidine may cause hypotension, so caution is advised when it is used in patients who have a history of orthostatic hypotension. Use caution with this drug as it can be very strong even at the 2 mg dose. Also use caution when switching from gel cap to tablet form and vice versa.



Tizanidine is available in tablets with "cor 138" on one side and 2 scores on the back that create an X, or R179 on one side and a single score through the middle of the back, or a white oval pill with R180 on one side and 2 scores on the back that create an X, or a round white tablet with E 44 on one side, and is double scored on the other side. It is also found as a circular white pill with the number 503 on one side and X-scored on the back[2].

Tizanidine is supplied as 2 and 4 mg tablets for oral administration, and in gel cap form in doses of 2 mg, 4 mg, and 6 mg.

The tablets are composed of the active ingredient, tizanidine hydrochloride (2.288 mg equivalent to 2 mg tizanidine base and 4.576 mg equivalent to 4 mg tizanidine base), and the inactive ingredients, silicon dioxide colloidal, stearic acid, microcrystalline cellulose and anhydrous lactose.

Side effects

Tizanidine use occasionally causes drug induced liver injury. In controlled clinical studies, approximately 5% of patients treated with Zanaflex had elevations of liver function tests (ALT, AST) to greater than 3 times the upper limit of normal (or 2 times if baseline levels were elevated).

Tizanidine use has been associated with hallucinations. Visual hallucinations and delusions have been reported in 5 of 170 patients (3%) in two North American controlled clinical studies.

If therapy needs to be discontinued, especially in patients who have been receiving high doses for long periods, the dose should be decreased slowly to minimize the risk of withdrawal and rebound hypertension, tachycardia, and hypertonia.


Concomitant use of tizanidine and moderate or potent CYP1A2 inhibitors is contraindicated. Concomitant use of tizanidine with fluvoxamine, a potent CYP1A2 inhibitor in man, resulted in a 33-fold increase in the tizanidine AUC (plasma drug concentration-time curve) by fluvoxamine.


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