Tizanidine

Pharmaceuticals -> Listed in ZINC15

Pharmaceuticals

1.4

1.05

slightly soluble

1.33e-01 g/L

Warning

H302+H332 (66.7%): Harmful if swallowed or if inhaled [Warning Acute toxicity, oral; acute toxicity, inhalation]

P203, P261, P264, P270, P271, P280, P301+P317, P304+P340, P317, P318, P330, P405, and P501 (click each P-code to see the statement)

Aggregated GHS information provided per 3 reports by companies from 3 notifications to the ECHA C&L Inventory. Each notification may be associated with multiple companies.

Should overdose occur, basic steps to ensure the adequacy of an airway and the monitoring of cardiovascular and respiratory systems should be undertaken. In general, symptoms resolve within one to three days following discontinuation of tizanidine and administration of appropriate therapy. Due to the similar mechanism of action, symptoms and management of tizanidine overdose are similar to those following clonidine overdose. (L1712)

Transient and asymptomatic elevations in serum ALT greater than 3 times the upper limit of normal occur in ~5% of patients taking tizanidine compared to 0.4% of subjects on placebo. Reports of severe hepatotoxicity, acute liver failure and death have been mentioned in review articles on tizanidine, but few case reports have been published. In these reports, the latency to onset of jaundice has ranged from 2 to 14 weeks and the enzyme elevations have been both cholestatic and hepatocellular (Case 1). Immunoallergic and autoimmune features have not been mentioned. Recovery was complete after 1 to 2 months.

M03BX02

M - Musculo-skeletal system

QM - Musculo-skeletal system

**A note on spasticity** Spasticity is an increase in muscle accompanied by uncontrolled, repetitive contractions of skeletal muscles which are involuntary. The patient suffering from muscle spasticity may have reduced mobility and high levels of pain, contributing to poor quality of life and problems performing activities of personal hygiene and care. **General effects** Tizanidine is a rapidly acting drug used for the relief of muscle spasticity when it is required for performing specific activities. It acts as an agonist at Alpha-2 adrenergic receptor sites and relieves symptoms of muscle spasticity, allowing the continuation of normal daily activities. In animal models, tizanidine has not been shown to exert direct effects on skeletal muscle fibers or the neuromuscular junction, and has shown no significant effect on monosynaptic spinal reflexes (consisting of the communication between only 1 sensory neuron and 1 motor neuron). The frequency of muscle spasm and clonus are shown to be decreased by tizanidine. Tizanidine shows a stronger action on polysynaptic reflexes, which involve several interneurons (relay neurons) communicating with motor neurons stimulating muscle movement. **Effects on blood pressure and heart rate** This drug decreases heart rate and blood pressure in humans. Despite this, rebound hypertension and tachycardia along with increased spasticity can occur when tizanidine is abruptly discontinued.

Tizanidine reduces spasticity by causing presynaptic inhibition of motor neurons via agonist actions at Alpha-2 adrenergic receptor sites. This drug is centrally acting and leads to a reduction in the release of excitatory amino acids like glutamate and aspartate, which cause neuronal firing that leads to muscle spasm. The above reduction and excitatory neurotransmitter release results in presynaptic inhibition of motor neurons. The strongest effect of tizanidine has been shown to occur on spinal polysynaptic pathways. The anti-nociceptive and anticonvulsant activities of tizanidine may also be attributed to agonist action on Alpha-2 receptors. Tizanidine also binds with weaker affinity to the Alpha-1 receptors, explaining its slight and temporary effect on the cardiovascular system.