|Systematic (IUPAC) name|
|Oral, Intranasal, Injection|
|Biological half-life||2.54 hours|
|CAS Registry Number|
|Molecular mass||253.712 g/mol|
Tizanidine (trade names 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 low blood pressure, 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 1
- Pharmacology 2
- Interactions 3
- Side effects 4
- References 5
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). Fluoroquinolone antibiotics such as moxifloxacin, levofloxacin, and ciprofloxacin should also be avoided due to an increased serum concentration of tizanidine when administered concomitantly. Tizanidine is a potent sedative. It therefore 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 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.
- "Tizanidine is mainly metabolized by cytochrome P450 1A2 in vitro". Br J Clin Pharmacol 57 (3): 349–353. 2004.
- Zanaflex for Fibromyalgia
- Kamen, L.; Henney, HR.; Runyan, JD. (Feb 2008). "A practical overview of tizanidine use for spasticity secondary to multiple sclerosis, stroke, and spinal cord injury.". Curr Med Res Opin 24 (2): 425–39.
- UCDavis Health System - Poison Puzzler
- Tizanidine - PubMed Health