Tizanidine; Uses, Dosage, Side Effects, Interaction, Pregnancy

Tizanidine Hydrochloride is the hydrochloride salt form of tizanidine, an imidazoline derivative structurally similar to clonidine and an adrenergic agonist with muscle relaxant property. Tizanidine is a short-acting drug for the management of spasticity. Tizanidine is an agonist at a2-adrenergic receptor sites and presumably reduces spasticity by increasing presynaptic inhibition of motor neurons. In animal models, tizanidine has no direct effect on skeletal muscle fibers or the neuromuscular junction, and no major effect on monosynaptic spinal reflexes. Tizanidinestimulates alpha-2 adrenergic receptors in the central nervous system, thereby inhibiting presynaptic release of norepinephrine.

Mechanism of Action of Tizanidine

Tizanidine reduces spasticity by increasing presynaptic inhibition of motor neurons through agonist action at a2-adrenergic receptor sites. Tizanidine is a central-acting alpha2-adrenergic agonist which acts at presynaptic receptors. It is structurally and pharmacologically related to clonidine but has only 2—10% of clonidine’s antihypertensive potency. The antispasmodic activity of tizanidine results from agonism at central pre-synaptic alpha2-receptors. The response to agonism at these receptors is a decrease in the release of excitatory amino acids which in turn leads to inhibition of spinal motor neurons. In animal models, tizanidine has no direct effect on skeletal muscle fibers or the neuromuscular junction, and no major effect on monosynaptic spinal reflexes. The effects of tizanidine are greatest on polysynaptic pathways. The overall effect of these actions is thought to reduce the facilitation of spinal motor neurons.

Indications of Tizanidine

• Treatment of increased muscle tone associated with spasticity
• Muscle spasm
• Cluster headaches
• Acute low back pain
• Muscle spasticity
• Acute myofascial low back pain.
• Spondylosis
• Spondylarthrosis
• Cervical and lumbar syndromes
• Arthrosis of the large joints
• Obliterating atherosclerosis of the extremity vessels
• Diabetic angiopathy
• Low back pain syndrome6
• Painful reflex muscle spasm
• Post-cerebral stroke spasticity
• For the management of increased muscle tone associated with spasticity

Contra-Indications of Tizanidine

• Mental Disorder with Loss of Normal Personality & Reality
• Slow Heartbeat
• abnormally low blood pressure
• severe liver disease
• kidney disease with a reduction in kidney function
• Allergies to Alpha 2 Adrenergic Agonist

Dosage of Tizanidine

Strengths: 2mg; 4 mg; 6 mg

Muscle Spasm

• Initial dose: 2 mg orally every 6 to 8 hours as needed
• Peak effects occur in approximately 1 to 2 hours and last for 3 to 6 hours; treatment can be repeated as needed to a maximum of 3 doses in 24 hours; gradually increase dose by 2 to 4 mg at intervals of 1 to 4 days until the satisfactory reduction of muscle tone is achieved.
• Maximum single dose: 16 mg
• Maximum daily dose: 36 mg in 24 hours

Side Effects of Tizanidine

• “azole” antifungal medications (e.g.,  fluconazole, itraconazole, ketoconazole)
• beta-blockers (e.g., atenolol, propranolol, metoprolol)
• barbiturates (e.g., butalbital, pentobarbital, phenobarbital)
• benzodiazepines (e.g., chlordiazepoxide, clonazepam, diazepam, lorazepam)
• calcium channel blockers (e.g., nifedipine, diltiazem, verapamil, amlodipine, felodipine)
• carbamazepine
• mirtazapine
• montelukast
• norfloxacin
• ondansetron
• carbamazepine
• peginterferon alfa-2b
• phenytoin
• other selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine,sertraline)
• 5-HT3 antagonists (e.g., granisetron, ondansetron)
• tamsulosin
• thiazide diuretics (e.g., hydrochlorothiazide, indapamide)
• tricyclic antidepressants (e.g., nortriptyline, amitriptyline, imipramine, 

Pregnancy & Lactation

Pregnancy

Tizanidine has not been studied for use by pregnant women. In some animal studies, tizanidine caused birth defects and other pregnancy problems. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Lactation

It is not known if tizanidine passes into breast milk. If you are a breastfeeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breastfeeding. The safety and effectiveness of using tizanidine have not been established for children less than 18 years of age.

References

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