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.
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.
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.