Tizanidine

Tizanidine.svg

Tizanidine
Tizanidine.svg
INN
Drug class
Routes of administration	By mouth
Pregnancy category
Bioavailability	40%
Metabolism	Liver
Elimination half-life	2.5 hours
Excretion	Renal
Legal status
CAS Number	51322-75-9
PubChem	5487
DrugBank	DB00697
ChemSpider	5287
KEGG	D08689

Tizanidine is a muscle relaxant medication used to treat muscle spasticity due to conditions such as multiple sclerosis and spinal cord injury. It is marketed under the brand name Zanaflex among others. Tizanidine works by blocking nerve impulses (pain sensations) that are sent to the brain.

Medical uses

Tizanidine is primarily used for the management of muscle spasticity. It is particularly effective in conditions such as multiple sclerosis, spinal cord injury, and other disorders that cause muscle spasms. The medication is taken orally, and its effects typically begin within an hour of ingestion.

Mechanism of action

Tizanidine is an alpha-2 adrenergic receptor agonist. It works by inhibiting the release of excitatory amino acids in the spinal cord, which reduces the activity of motor neurons. This leads to a decrease in muscle tone and spasticity.

Side effects

Common side effects of tizanidine include drowsiness, dry mouth, dizziness, and asthenia (weakness). Less common but more severe side effects can include hypotension (low blood pressure), bradycardia (slow heart rate), and hepatotoxicity (liver damage). Patients are advised to monitor for signs of liver dysfunction and to have regular liver function tests.

Pharmacokinetics

Tizanidine has a bioavailability of approximately 40% when taken orally. It is metabolized in the liver and has an elimination half-life of about 2.5 hours. The drug and its metabolites are primarily excreted through the kidneys.

Contraindications

Tizanidine is contraindicated in patients with significant liver disease and those taking CYP1A2 inhibitors such as fluvoxamine and ciprofloxacin, as these can increase the concentration of tizanidine in the blood, leading to severe side effects.

Interactions

Tizanidine can interact with other medications, including antihypertensives, which can enhance the blood pressure-lowering effects, and CNS depressants, which can increase sedation. It is important to inform healthcare providers of all medications being taken to avoid potential interactions.

See also

• Muscle relaxant
• Multiple sclerosis
• Spinal cord injury
• Alpha-2 adrenergic receptor