Tizanidine

Names
Pronunciation	/taɪˈzænɪdiːn/tye-ZAN-i-deen
Trade names	Zanaflex, Sirdalud, and others
Other names	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
IUPAC name 5-Chloro-N-(4,5-dihydro-1H-imidazol-2-yl)benzo[c] [1,2,5]thiadiazol-4-amine
Clinical data
Pregnancy category	C
Routes of use	By mouth (tablets,capsules)
Defined daily dose	12 mg[1]
External links
AHFS/Drugs.com	Monograph
MedlinePlus	a601121
Legal
Legal status	UK: POM (Prescription only) US: ℞-only
Pharmacokinetics
Bioavailability	~40%[2]
Protein binding	~30%
Metabolism	Liver (CYP1A2, 95%)
Eliminationhalf-life	2.54 hours (tizanidine), 20–40 hours (inactive metabolites)[2]
Excretion	Urine (60%),feces (20%)
Chemical and physical data
Formula	C9H8ClN5S
Molar mass	253.71 g·mol−1
3D model (JSmol)	Interactive image
SMILES Clc1ccc3nsnc3c1NC/2=N/CCN\2
InChI InChI=1S/C9H8ClN5S/c10-5-1-2-6-8(15-16-14-6)7(5)13-9-11-3-4-12-9/h1-2H,3-4H2,(H2,11,12,13) Y Key:XFYDIVBRZNQMJC-UHFFFAOYSA-N Y

Tizanidine, sold under the brand nameZanaflex among others, is a medication used to treatmuscle spasticity due tospinal cord injury ormultiple sclerosis.^[3] Effectiveness appears similar tobaclofen ordiazepam.^[4] It is taken by mouth.^[5]

Common side effects include dry mouth, sleepiness, weakness, and dizziness.^[5] Serious side effects may includelow blood pressure,liver problems,psychosis, andQT prolongation.^[5] It is unclear if use inpregnancy andbreastfeeding is safe.^[6] It is anα2-adrenergic agonist and how it works is not entirely clear.^[5]

Tizanidine was approved for medical use in the United States in 1996.^[5] It is available as ageneric medication.^[3] A month supply in the United Kingdom costs theNHS about 3.45 £ as of 2019.^[3] In the United States the wholesale cost of this amount is about US$4.20.^[7] In 2017, it was the 89th most prescribed medication in the United States, with more than nine million prescriptions.^[8][9]

Medical uses

Tizanidine has been found to be as effective as other antispasmodic drugs and is more tolerable thanbaclofen anddiazepam.^[4]

Dosage

Thedefined daily dose is 12 mg by mouth.^[1]

Side effects

Side effects include dizziness, drowsiness, weakness, nervousness, hallucinations, depression, vomiting, dry mouth, constipation, diarrhea, stomach pain, heartburn, increased muscle spasms, back pain, rash, sweating, and a tingling sensation in the arms, legs, hands, and feet.^[10]

Interactions

Concomitant use of tizanidine and moderate or potentCYP1A2 inhibitors (such aszileuton, certain antiarrhythmics (amiodarone,mexiletine,propafenone,verapamil),cimetidine,famotidine,aciclovir,ticlopidine andoral contraceptives) is contraindicated. Concomitant use of tizanidine withfluvoxamine, a potent CYP1A2 inhibitor in humans, resulted in a 33-fold increase in the tizanidineAUC (plasma drug concentration-time curve).^[2] For this reason bothfluvoxamine and tizanidine should not be taken at the same time. Fluoroquinolone antibiotics such asmoxifloxacin,levofloxacin, andciprofloxacin should also be avoided due to an increased serum concentration of tizanidine when administered concomitantly.^[11] Tizanidine has the potential to interact with othercentral nervous system depressants. Alcohol should be avoided, particularly as it can upset the stomach. The CNS-depressant effects of tizanidine and alcohol are additive.^[2] Caution with the followinginteractions:^[12][13][14]

• antibiotics such asenoxacin,gatifloxacin,levofloxacin,lomefloxacin,moxifloxacin,ofloxacin,sparfloxacin,trovafloxacin , ornorfloxacin;
• blood pressure medications such asclonidine,guanabenz,guanfacine (Tenex), ormethyldopa;
• heart rhythm medications such asamiodarone (Cordarone, Pacerone),mexiletine (Mexitil),propafenone (Rhythmol), andverapamil (Calan, Covera, Isoptin).

Pharmacology

Tizanidine is an α2 agonist closely related to clonidine. It has approximately one tenth to one fifteenth of the pressure lowering effect of clonidine. The relation between the α2 receptor agonism and the spasmolytic action is still not fully understood.^[15]

Route of administration

Tizanidine is available as a tablet or capsule. Capsules may be opened and sprinkled on food. However, this may change the absorption of the medication compared to taking the capsule whole.^[16]

Chemistry

It has avolume of distribution of 2.4 L/kg following intravenous administration.^[2]

Society and culture

Cost

A month supply in the United Kingdom costs theNHS about 3.45 £ as of 2019.^[3] In the United States the wholesale cost of this amount is about US$4.20.^[7] In 2017, it was the 89th most prescribed medication in the United States, with more than nine million prescriptions.^[8][9]

• 

  Tizanidine costs (US)

• 

  Tizanidine prescriptions (US)

References

Further reading

• Gelber, David A.; Good, David C.; Dromerick, Alexander; Sergay, Stephen; Richardson, Melissa (August 2001)."Open-Label Dose-Titration Safety and Efficacy Study of Tizanidine Hydrochloride in the Treatment of Spasticity Associated With Chronic Stroke".Stroke.32 (8): 1841–1846.doi:10.1161/01.STR.32.8.1841.ISSN 0039-2499. Retrieved14 November 2024.

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