Tizanidine | Muscle Relaxant | CAS 51322-75-9

Product Name: Tizanidine
CAS No.: 51322-75-9 (base)
Chemical Name: 5-chloro-N-(4,5-dihydro-1H-imidazol-2-yl)-2,1,3-benzothiadiazol-4-amine
Molecular Formula: C₉H₈ClN₅S
Appearance: White or almost white crystalline powder
Solubility: Practically insoluble in water; soluble in methanol and acetic acid. Often used as the hydrochloride salt, which is more water-soluble.
Stability: Relatively stable when stored

1. Introduction

Tizanidine is a centrally acting muscle relaxant, an α₂-adrenergic receptor agonist. It reduces muscle spasm and increased skeletal muscle tone by inhibiting polysynaptic reflexes at the spinal cord level. It is used for painful muscle spasms and spasticity.

Increased muscle tone and spasticity are common symptoms of various neurological diseases (e.g., multiple sclerosis, stroke, spinal cord injuries) and conditions associated with musculoskeletal disorders. Tizanidine, acting at the level of the central nervous system, promotes skeletal muscle relaxation, reduces pain, and improves motor function.

2. Chemical Structure & Synthesis

Structurally, tizanidine is an imidazoline derivative, similar to clonidine.

Synthesis: Tizanidine is synthesized in several stages. One approach involves the reaction of 4-amino-5-chloro-2,1,3-benzothiadiazole with 2-chloro-4,5-dihydro-1H-imidazole or its precursors.

3. Mechanism of Action

Tizanidine is a selective agonist of α₂-adrenergic receptors, primarily presynaptic, located in the spinal cord. Stimulation of these receptors leads to inhibition of excitatory amino acid (glutamate and aspartate) release from presynaptic terminals of spinal cord interneurons. This, in turn, suppresses polysynaptic reflexes at the spinal cord level responsible for maintaining increased muscle tone. Tizanidine also has moderate centrally acting analgesic effects.

4. Pharmacokinetics

Rapidly and almost completely absorbed after oral administration. Undergoes significant first-pass metabolism in the liver (via CYP1A2), resulting in relatively low bioavailability (approximately 40%). Moderate plasma protein binding (approximately 30%). Excreted primarily by the kidneys as inactive metabolites.

5. Applications

• Painful muscle spasms associated with static and functional disorders of the spine (cervical and lumbar syndromes)

• Painful muscle spasms after surgical interventions (e.g., for intervertebral disc herniation or hip osteoarthritis)

• Skeletal muscle spasticity in neurological disorders:

  • Multiple sclerosis

  • Chronic myelopathy

  • Degenerative spinal cord diseases

  • Consequences of cerebrovascular accidents (stroke)

  • Cerebral palsy (in patients over 18 years of age)

  • Traumatic brain or spinal cord injury

6. Conclusion

Tizanidine is an effective centrally acting muscle relaxant for the treatment of painful muscle spasms and spasticity of various origins. Its mechanism of action, associated with α₂-adrenergic receptor stimulation, provides muscle tone reduction and pain relief. The use of tizanidine may be accompanied by side effects such as drowsiness, dry mouth, and hypotension, requiring individual dose selection and caution, especially at the beginning of treatment.