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Tizanidine

Drug Reference 9 min 1629

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Created On: 01/10/2019

Tizanidine is a central alpha 2-adrenergic agonist.

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Introduction

Tizanidine is a central alpha 2-adrenergic agonist. It is a short-acting muscle relaxant for the management of spasticity by temporarily relaxing the muscle tones. It works by blocking nerve impulses that are sent to the brain. The effects of tizanidine are greatest on polysynaptic pathways.

Pharmacological class: Muscle Relaxant

Indications

Muscle spasms

Pharmachologic action

Tizanidine is a short-acting muscle relaxant. It acts by reducing the spasticity by increasing the presynaptic inhibition of motor neurons through agonist action at 2-adrenergic receptor sites. The overall effect of these actions is thought to reduce the facilitation of spinal motor neurons. The effects of tizanidine are greatest on polysynaptic pathways.

Dosage

Muscle spasms: 4 mg orally every 6 to 8 hours

Pharmacokinetics

Tizanidine is completely absorbed following oral administration due to extensive first-pass hepatic metabolism. It is extensively distributed throughout the body with a mean steady state volume of distribution of 2.4 L/kg (CV = 21%) following intravenous administration in healthy adult volunteers. Tizanidine is approximately 30% bound to plasma proteins. Approximately 95% of an administered dose is metabolized. The primary cytochrome P450 isoenzyme involved in tizanidine metabolism is CYP1A2. An average of 60% and 20% of total radioactivity was recovered in the urine and feces, respectively.

Contraindications

Contraindicated in patients taking potent inhibitors of CYP1A2, such as fluvoxamine or ciprofloxacin.

Drug interaction

Concomitant intake of tizanidine and amiloride may have additive effects in lowering blood pressure
Concomitant use of ciprofoxacin and tizanidine results in decreased blood pressure, increased drowsiness, and increased psychomotor impairment
when administered with alcohol, it may increase the overall amount of drug & frequency of adverse reactions
Concomitant use of tizanidine with CNS depressants may be additive as excess sedation may result

Side effects

Common (affecting between 1 in 10 to 1 in 100):

Fever or chills
Chest pain
Nausea and vomiting
Nervousness
Pain or burning while urinating
Tiredness

Uncommon (affecting 1 in 100 to 1 in 1000):

Flu-like symptoms
Blurred vision
Irregular heartbeat
Itching skin
Kidney stones
Right upper stomach tenderness
Shortness of breath
Weight gain

Very rare (affecting less than 1 in 10,000):

Hepatic failure
Hallucinations
Insomnia
Sleep disorders
Muscular weakness

Precautions

Avoid in patients who are allergic to tizanidine
Avoid in patients taking ciprofloxacin or fluvoxamine
Avoid in patients who have or have ever had kidney or liver disease
Do not drive or use machinery, as tizanidine can cause dizziness
Avoid alcohol, as it can add to the drowsiness caused by tizanidine

Clinical evidence

In a study, tizanidine has been shown to be effective in reducing spasticity secondary to multiple sclerosis. The multicenter study assessed the efficacy and safety of oral tizanidine in patients who had spinal cord injury of > 12-month duration. Out of 124 patients in the study, 78 completed it. Muscle tone, assessed by Ashworth score, was significantly reduced (p = 0.0001) by tizanidine treatment in comparison with placebo.¹

References

Neurology. 1994 Nov;44(11 Suppl 9):S34-42; discussion S42-3.
http://www.medicinenet.com/tizanidine-oral/article.htm
http://www.rxlist.com/zanaflex-drug.htm
https://www.nlm.nih.gov/medlineplus/druginfo/meds/a601121.html
http://www.drugs.com/tizanidine.html
http://www.drugbank.ca/drugs/DB00697
http://www.drugs.com/answers/thr-drug-legal-drug-classification-zanaflex-589901.html