Tizanidine

Tizanidine

Systematic (IUPAC) name
5-chloro-N-(4,5-dihydro-1H-imidazol-2-yl)benzo[c][1,2,5]thiadiazol-4-amine
Clinical data
Trade names	Zanaflex
AHFS/Drugs.com	monograph
MedlinePlus	a601121
Pregnancy category	C
Legal status	US: ℞-only
Routes of administration	Oral, Intranasal, Injection
Pharmacokinetic data
Protein binding	30%
Metabolism	CYP 1A2
Biological half-life	2.54 hours
Identifiers
CAS Number	51322-75-9 Y
ATC code	M03BX02 (WHO)
PubChem	CID: 5487
DrugBank	DB00697 Y
ChemSpider	5287 Y
UNII	6AI06C00GW Y
KEGG	D08611 Y
ChEMBL	CHEMBL1079 Y
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
Molecular mass	253.712 g/mol
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
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Tizanidine (trade names Relentus from Beximco Pharma, Zanaflex, Sirdalud) is a drug that is used as a muscle relaxant. It is a centrally acting α₂ adrenergic agonist. It is used to treat the spasms, cramping, and tightness of muscles caused by medical problems such as multiple sclerosis, ALS, 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.

Tizanidine has been found to be as effective as other antispasmodic drugs and has superior tolerability to that of baclofen and diazepam. Tizanidine can be very strong even at the 2 mg dose and may cause hypotension, so caution is advised when it is used in patients who have a history of orthostatic hypotension, or when switching from gel cap to tablet form and vice versa.

Tizanidine can occasionally cause liver damage, generally the hepatocellular type. Clinical trials show that up to 5% of patients treated with tizanidine had elevated liver function test values, though symptoms disappeared upon withdrawal of the drug. Care should be used when first beginning treatment with tizanidine with regular liver tests for the first 6 months of treatment.

Availability

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.

Interactions

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). Fluoroquinolone antibiotics such as moxifloxacin, levofloxacin, and ciprofloxacin should also be avoided due to an increased serum concentration of tizanidine when administered concomitantly. Tizanidine has the potential to interact with other CNS depressants. Alcohol should be avoided, particularly as it can upset the stomach.

It has a volume of distribution of 2.6L (per manufacturers notes).

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.