Tizanidine

Tizanidine (brandnames Zanaflex, Sirdalud) is a drug which is used as a muscle relaxant. It is a centrally acting α-2 adrenergic agonist. It is used to treat the spasms, cramping, and tightness of muscles caused by medical problems such as multiple sclerosis, spastic diplegia, back pain, or certain other injuries to the spine or central nervous system. It is also prescribed off-label as a sleep aid, seizure inhibitor, and for some symptoms of fibromyalgia[1].
Tizanidine may cause hypotension so caution is advised when it is used in patients who have a history of orthostatic hypotension.
Tizanidine can come in tablets with "cor 138" on one side and 2 scores on the back that create an X, or R179 on one side and a single score through the middle of the back, or a white oval pill with R180 on one side and 2 scores on the back that create an X. It's also found as a circular white pill with the number 503 on one side and X-scored on the back[2].
It is supplied as 2 and 4 mg tablets for oral administration, and in gel cap form in doses of 2mg, 4mg, and 6mg.
The tablets are composed of the active ingredient, tizanidine hydrochloride (2.288 mg equivalent to 2 mg tizanidine base and 4.576 mg equivalent to 4 mg tizanidine base), and the inactive ingredients, silicon dioxide colloidal, stearic acid, microcrystalline cellulose and anhydrous lactose.