WARNING AND CAUTIONS

5 WARNINGS AND PRECAUTIONS • Hypotension: monitor for signs and symptoms of hypotension, in particular in patients receiving concurrent antihypertensives; tizanidine should not be used with other α 2 -adrenergic agonists ( 5.1 , 7.7 ) • Risk of liver injury: monitor ALTs; discontinue tizanidine if liver injury occurs ( 5.2 ) • Sedation: Tizanidine may interfere with everyday activities; sedative effects of tizanidine, alcohol, and other CNS depressants are additive ( 5.3 , 7.5 , 7.6 ) • Hallucinations: consider discontinuation of tizanidine ( 5.4 ) • Less potent inhibitors of CYP1A2: may cause hypotension, bradycardia, or excessive drowsiness, use caution if tizanidine is used with less potent inhibitors of CYP1A2, e.g., zileuton, other fluoroquinolones, antiarrythmics, cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine ( 5.5 , 7.3 , 12.3 ) • Renal impairment (creatinine clearance < 25 mL/min): use tizanidine with caution, and monitor closely for dry mouth, somnolence, asthenia and dizziness as indicators of potential overdose ( 5.7 ) 5.1 Hypotension Tizanidine is an α 2 -adrenergic agonist that can produce hypotension.

Syncope has been reported in the post-marketing setting.

The chance of significant hypotension may possibly be minimized by titration of the dose and by focusing attention on signs and symptoms of hypotension prior to dose advancement.

In addition, patients moving from a supine to fixed upright position may be at increased risk for hypotension and orthostatic effects.

Monitor for hypotension when tizanidine is used in patients receiving concurrent antihypertensive therapy.

It is not recommended that tizanidine be used with other α 2 -adrenergic agonists.

Clinically significant hypotension (decreases in both systolic and diastolic pressure) has been reported with concomitant administration of either fluvoxamine or ciprofloxacin and single doses of 4 mg (base) of tizanidine.

Therefore, concomitant use of tizanidine with fluvoxamine or with ciprofloxacin, potent inhibitors of CYP1A2, is contraindicated [see Contraindications (4) and Drug Interactions (7.1 , 7.2) ] .

5.2 Risk of Liver Injury Tizanidine may cause hepatocellular liver injury.

Tizanidine should be used with caution in patients with any hepatic impairment.

Monitoring of aminotransferase levels is recommended for baseline and 1 month after maximum dose is achieved, or if hepatic injury is suspected [see Dosage and Administration (2.3) and Use in Specific Populations (8.7) ] .

5.3 Sedation Tizanidine can cause sedation, which may interfere with everyday activity.

In the multiple dose studies, the prevalence of patients with sedation peaked following the first week of titration and then remained stable for the duration of the maintenance phase of the study.

The CNS depressant effects of tizanidine with alcohol and other CNS depressants (e.g., benzodiazepines, opioids, tricyclic antidepressants) may be additive.

Monitor patients who take tizanidine with another CNS depressant for symptoms of excess sedation [see Drug Interactions (7.5 , 7.6) ] .

5.4 Hallucinosis/Psychotic-Like Symptoms Tizanidine use has been associated with hallucinations.

Formed, visual hallucinations or delusions have been reported in 5 of 170 patients (3%) in two North American controlled clinical studies.

Most of the patients were aware that the events were unreal.

One patient developed psychosis in association with the hallucinations.

One patient among these 5 continued to have problems for at least 2 weeks following discontinuation of tizanidine.

Consider discontinuing tizanidine in patients who develop hallucinations.

5.5 Interaction with CYP1A2 Inhibitors Because of potential drug interactions, tizanidine is contraindicated in patients taking potent CYP1A2 inhibitors, such as fluvoxamine or ciprofloxacin.

Adverse reactions such as hypotension, bradycardia, or excessive drowsiness can occur when tizanidine is taken with other CYP1A2 inhibitors, such as zileuton, fluoroquinolones other than ciprofloxacin (which is contraindicated), antiarrythmics (amiodarone, mexiletine, propafenone), cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine).

Concomitant use should be avoided unless the necessity for tizanidine therapy is clinically evident.

In such a case, use with caution [see Drug Interactions (7.3) and Clinical Pharmacology (12.3) ] .

5.6 Hypersensitivity Reactions Tizanidine can cause anaphylaxis.

Signs and symptoms including respiratory compromise, urticaria, and angioedema of the throat and tongue have been reported.

Patients should be informed of the signs and symptoms of severe allergic reactions and instructed to discontinue tizanidine and seek immediate medical care should these signs and symptoms occur [see Contraindications (4) ] .

5.7 Increased Risk of Adverse Reactions in Patients with Renal Impairment Tizanidine should be used with caution in patients with renal insufficiency (creatinine clearance < 25 mL/min), as clearance is reduced by more than 50%.

In these patients, during titration, the individual doses should be reduced.

If higher doses are required, individual doses rather than dosing frequency should be increased.

These patients should be monitored closely for the onset or increase in severity of the common adverse events (dry mouth, somnolence, asthenia and dizziness) as indicators of potential overdose [see Dosage and Administration (2.2) and Use in Specific Populations (8.6) ] .

5.8 Withdrawal Adverse Reactions Withdrawal adverse reactions include rebound hypertension, tachycardia, and hypertonia.

To minimize the risk of these reactions, particularly in patients who have been receiving high doses (20 mg (base) to 28 mg (base) daily) for long periods of time (9 weeks or more) or who may be on concomitant treatment with narcotics, the dose should be decreased slowly (2 mg (base) to 4 mg (base) per day) [see Dosage and Administration (2.2) ] .