Tizanidine is an imidazole derivative with agonistic action at both spinal and supraspinal a2 adrenergic receptors. It acts to prevent the release of excitatory amino acids and substance P from the presynaptic terminals of spinal interneurons.
Tizanidine may also facilitate the inhibitory actions of glycine, suppress acetylcholine-induced excitation of Renshaw cell activity and exert antinociceptive actions. As an a2 adrenergic agonist, tizanidine slows the firing of neurons in the locus ceruleus.
This leads to inhibition of the facilitatory activity that the brainstem nucleus exerts upon reflex activity in the lumbar portion of the spinal cord.
References:
Delwaide PJ, Pennisi G. Tizanidine and electrophysiologic analysis of spinal control mechanisms in humans with spasticity. Neurology 1994;44(suppl 9):S21-8.
The United Kingdom Tizanidine Trial Group. A double-blind, placebo-controlled trial of tizanidine in the treatment of spasticity caused by multiple sclerosis. Neurology 1994;44(suppl 9):S70-8.
Article Index
Page 15 of 18