Overview
11 DESCRIPTION Tizanidine Tablets, USP contains tizanidine hydrochloride as the active ingredient, which is a central alpha 2 -adrenergic agonist. Its chemical name is 5-chloro-4-(2-imidazolin-2-ylamino)-2,1,3-benzothiodiazole monohydrochloride. It has a molecular formula of C 9 H 8 CIN 5 S·HCl and a molecular weight of 290.17.
Mechanism of Action
12 CLINICAL PHARMACOLOGY 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. 12.2 Pharmacodynamics The CNS depressant effects of tizanidine and alcohol are additive [see Warnings and Precautions ( 5.3 ) and Drug Interactions (7.4)]. 12.3 Pharmacokinetics Tizanidine has linear pharmacokinetics over the doses studied in clinical development [1 mg (half the recommended dosage) to 20 mg].
Indications
- 1 INDICATIONS AND USAGE Tizanidine is indicated for the treatment of spasticity in adults. Tizanidine is a central alpha-2-adrenergic agonist indicated for the treatment of spasticity. (1)
Common Doses
- 2 mg
- 4 mg
- 36 mg
- 25 mL
Dosage
2 DOSAGE AND ADMINISTRATION Monitoring of aminotransferase levels is recommended at baseline and 1 month after maximum dose is achieved. ( 2.1 ) Recommended starting dose: 2 mg by mouth every 6 to 8 hours, as needed, up to a maximum of 3 doses in 24 hours ( 2.2 ) Dosage can be increased by 2 mg to 4 mg per dose every 1 to 4 days; maximum total daily dosage is 36 mg ( 2.2 ) Tizanidine pharmacokinetics differs between tablets and capsules, and when taken with or without food. These differences could result in a change in tolerability and control of symptoms.
Contraindications
- 4 CONTRAINDICATIONS Tizanidine is contraindicated in patients: • taking strong CYP1A2 inhibitors [see Drug Interactions ( 7.1 )]. • with a history of hypersensitivity to tizanidine or the ingredients in tizanidine tablets. Symptoms have included anaphylaxis and angioedema [see Warnings and Precautions ( 5.5 )]. Concomitant use with strong CYP1A2 inhibitors ( 4 , 7.1 ) Patients with a history of hypersensitivity to tizanidine or the ingredients in tizanidine tablets ( 4 , 5.5 )
Side Effects
- 6 ADVERSE REACTIONS The following clinically significant 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 ( 5.5 )] • Withdrawal Adverse Reactions [ see Warnings and Precautions ( 5.
Interactions
- 7 DRUG INTERACTIONS Moderate or weak CYP1A2 inhibitors: avoid concomitant use; may cause hypotension, bradycardia, or excessive drowsiness; if concomitant use is necessary and adverse reactions occur, reduce tizanidine dosage or discontinue. ( 7.2 , 12.3 ) 7.1 Strong CYP1A2 Inhibitors Concomitant use of tizanidine with strong cytochrome P450 1A2 (CYP1A2) inhibitors (e.g., fluvoxamine, ciprofloxacin) is contraindicated.