Overview
Tizanidine hydrochloride is a central alpha2-adrenergic agonist. Tizanidine hydrochloride, USP is a white to off-white, fine crystalline powder, which is odorless or with a faint characteristic odor. Tizanidine is slightly soluble in water and methanol; solubility in water decreases as the pH increases.
Mechanism of Action
12.1 Mechanism of action Tizanidine is a central alpha-2-adrenergic receptor agonist and presumably reduces spasticity by increasing presynaptic inhibition of motor neurons. The effects of tizanidine are greatest on polysynaptic pathways. The overall effect of these actions is thought to reduce facilitation of spinal motor neurons. 12.3 Pharmacokinetics Absorption and Distribution Following oral administration, tizanidine is essentially completely absorbed. The absolute oral bioavailability of tizanidine is approximately 40% (CV = 24%), due to extensive first-pass hepatic metabolism. Tizanidine is extensively distributed throughout the body with a mean steady state volume of distribution of 2.4 L/kg (CV = 21%) following intravenous administration in healthy adult volunteers.
Indications
- Tizanidine is a central alpha-2-adrenergic agonist indicated for the management of spasticity. Because of the short duration of therapeutic effect, treatment with tizanidine should be reserved for those daily activities and times when relief of spasticity is most important [see Dosage and Administration (2.1)].
Common Doses
- 2 mg
- 4 mg
- 36 mg
- 16 mg
Dosage
2.1 Dosing Information Tizanidine tablets may be prescribed with or without food. Once the formulation has been selected and the decision to take with or without food has been made, this regimen should not be altered. Food has complex effects on tizanidine pharmacokinetics, which differ with the different formulations. Tizanidine Capsules and tizanidine tablets are bioequivalent to each other under fasting conditions (more than 3 hours after a meal), but not under fed conditions (within 30 minutes of a meal).
Contraindications
- Tizanidine is contraindicated in patients taking potent inhibitors of CYP1A2, such as fluvoxamine or ciprofloxacin [see Drug Interactions (7.1, 7.2)].
Side Effects
- The following adverse reactions are described elsewhere in other sections of the prescribing information: Hypotension [see Warnings and Precautions (5.1)] Liver Injury [see Warnings and Precautions (5.2)] Sedation [see Warnings and Precautions (5.3)] Hallucinosis/Psychotic-Like Symptoms [see Warnings and Precautions (5.4)] Hypersensitivity Reactions [see Warnings and Precautions (5.6)] 6.1 Clinical Trials Experience Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in the clinical studies of a drug cannot be directly compared to rates in...
Interactions
- 7.1 Fluvoxamine Concomitant use of fluvoxamine and tizanidine is contraindicated. Changes in pharmacokinetics of tizanidine when administered with fluvoxamine resulted in significantly decreased blood pressure, increased drowsiness, and increased psychomotor impairment. [see Contraindications (4) and Clinical Pharmacology (12.3)] 7.2 Ciprofloxacin Concomitant use of ciprofoxacin and tizanidine is contraindicated. Changes in pharmacokinetics of tizanidine when administered with ciprofloxacin resulted in significantly decreased blood pressure, increased drowsiness, and increased psychomotor...