Tizanidin

Tizanidine is a so-called alpha-2-receptor agonist and a representative of the group of centrally acting muscle relaxants. The main areas of application are the treatment of painful muscle tension, for example due to spinal complaints, the treatment after operations (e.g.: after herniated disc) or the symptomatic treatment of multiple sclerosis. Tizanidine requires a prescription and is mainly given in the form of tablets or capsules.

Pharmacodynamics

Tizanidine binds with high affinity to alpha-2-adrenoreceptors, primarily in the patient's spinal cord. This inhibits the activity of excitatory amino acids, which are responsible for the excessive muscle tone. In addition to its relaxing effect, tizanidine also has moderate analgesic properties.

Pharmacokinetics

Tizanidine is absorbed through the intestine. Oral bioavailability is only 40% which is why the dose should be adjusted accordingly. Tizanidine is bound to plasma proteins at a rate of approximately 30%. The drug is degraded in the liver by the enzyme CYP1A2. The half-life averages about 2.5 hours and final elimination is almost entirely by the kidneys.

Drug interactions

Drugs that inhibit the enzyme CYP1A2 should not be taken concomitantly with tizanidine, as life-threatening elevated plasma levels of the drug may occur. These include: Fluvoxamine, ciprofloxacin, amiodarone, propafenone and mexiletine, cimetidine and some fluoroquinolones. Furthermore, a combination with the following substances is contraindicated: QT interval prolonging substances, antihypertensives, diuretics, beta-blockers, oral contraceptives and alcohol or other centrally depressant substances.

Possible side effects are:

• Drowsiness, fatigue, dizziness.
• bradycardia, tachycardia
• hypotension, rebound hypertension
• dry mouth, nausea, gastrointestinal disturbances

Use during pregnancy or lactation is not recommended. Tizanidine should be used here only if the benefit clearly outweighs the risk.

Toxicological data

LD50 (rat, oral): 414 mg/kg