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Systematic (IUPAC) name
Clinical data
Routes of
Oral, Intranasal, Injection
Legal status
Legal status
  • Rx-Only, Unscheduled
Pharmacokinetic data
Protein binding 30%
Metabolism CYP 1A2
Biological half-life 2.54 hours
CAS Number 51322-75-9
ATC code M03BX02 (WHO)
PubChem CID 5487
DrugBank APRD00128
ChemSpider 5287
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
Chemical data
Formula C9H8ClN5S
Molar mass 253.712[[Script error: No such module "String".]]
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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 has been found to be as effective as other antispasmodic drugs and have superior tolerability than baclofen and diazepam.[2] 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[3]. You may also come across a white round tablet that is X-scored with what appears to be, on the opposite side, an uppercase "A" with a horizontal line through the right half of the letter, somewhat like a "G" and the numbers 594.[4] It is also found as a round white tablet with 2 scores on the back which create an X and the letters R L on the other side. This is certainly a 4mg tablet and could also be a 2mg.

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.


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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es:Tizanidina hu:Tizanidin pl:Tizanidyna ru:Тизанидин

  1. Zanaflex for Fibromyalgia
  2. Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  3. http://www.pharmer.org/images/domestic/tizanidine-503
  4. http://www.drugs.com/tizanidine-images.html