Tizanidine-d₄is intended for use as an internal standard for the quantification of tizanidine by GC- or LC-MS. Tizanidine is an α₂-adrenergic receptor (α₂-AR) agonist.¹Administration of tizanidine reduces neuronal excitation induced by noxious stimuli and depresses spontaneous neuronal firing in anesthetized cats. Tizanidine-induced neuronal depression is reversed by the selective α₂-AR antagonist RX781094 but not the α₁-AR antagonists prazosin and WB-4101. It acts as a muscle relaxant that inhibits α- and γ-rigidity in rats, reflex muscle tone in rabbits, and the linguomadibular reflex in cats without sedative, hemodynamic, or neurochemical effects.²Formulations containing tizanidine have been used for the treatment of stiff-person syndrome and to improve gait function in patients with incomplete spinal cord injuries.^3,4

1.Davies, J., and Quinlan, J.E.Selective inhibition of responses of feline dorsal horn neurons to noxious cutaneous stimuli by tizanidine (DS103-282) and noradrenaline: Involvement of α2-adrenoceptorsNeuroscience16(3)673-682(1985) 2.Sayers, A.C., BÜrki, H.R., and Eichenberger, E.The pharmacology of 5-chloro-4-(2-imidazolin-2-yl-amino)-2,1,3-benzothiadiazole (DS 103-282), a novel myotonolytic agentArzneimittelforschung30(5)793-803(1980) 3.Meinck, H.-M., Ricker, K., and Conrad, B.The stiff-man syndrome: New pathophysiological aspects from abnormal exteroceptive reflexes and the response to clomipramine, clonidine, and tizanidineJ. Neurol. Neurosurg. Psychiatry47(3)280-287(1984) 4.Duffell, L.D., Brown, G.L., and Mirbagheri, M.M.Facilitatory effects of anti-spastic medication on robotic locomotor training in people with chronic incomplete spinal cord injuryJ. Neuroeng. Rehabil.1229(2015)