2.1 Dosing Information

Zanaflex Capsules ® or Zanaflex ® 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. Zanaflex Capsules and Zanaflex 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). These pharmacokinetic differences may result in clinically significant differences when switching administration of tablet and capsules and when switching administration between the fed or fasted state. These changes may result in increased adverse events, or delayed or more rapid onset of activity, depending upon the nature of the switch. For this reason, the prescriber should be thoroughly familiar with the changes in kinetics associated with these different conditions [ see Clinical Pharmacology (12.3)].

The recommended starting dose is 2 mg. Because the effect of Zanaflex peaks at approximately 1 to 2 hours post-dose and dissipates between 3 to 6 hours post-dose, treatment can be repeated at 6 to 8 hour intervals, as needed, to a maximum of three doses in 24 hours.

Dosage can be gradually increased by 2 mg to 4 mg at each dose, with 1 to 4 days between dosage increases, until a satisfactory reduction of muscle tone is achieved. The total daily dose should not exceed 36 mg. Single doses greater than 16 mg have not been studied.

2.2 Dosing in Patients with Renal Impairment

Zanaflex 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 [ see Warnings and Precautions (5.7)].

2.3 Dosing in Patients with Hepatic Impairment

Zanaflex should be used with caution in patients with any hepatic impairment. 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. Monitoring of aminotransferase levels is recommended for baseline and 1 month after maximum dose is achieved, or if hepatic injury is suspected. [ see Use in Specific Populations (8.7)]

2.4 Drug Discontinuation

If therapy needs to be discontinued, particularly in patients who have been receiving high doses (20 mg to 36 mg daily) for long periods (9 weeks or more) or who may be on concomitant treatment with narcotics, the dose should be decreased slowly (2 mg to 4 mg per day) to minimize the risk of withdrawal and rebound hypertension, tachycardia, and hypertonia [ see Drug Abuse and Dependence (9.3)].

Capsules

2 mg: Light blue opaque body with a light blue opaque cap with "2 MG" printed on the cap
4 mg: White opaque body with a blue opaque cap with "4 MG" printed on the cap
6 mg: Blue opaque body with a white stripe and blue opaque cap with "6 MG" printed on the cap

Tablets

4 mg white, uncoated tablets with a quadrisecting score on one side and debossed with "A594" on the other side

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 Zanaflex is used in patients receiving concurrent antihypertensive therapy. It is not recommended that Zanaflex 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 of Zanaflex. Therefore, concomitant use of Zanaflex 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

Zanaflex may cause hepatocellular liver injury. Zanaflex 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

Zanaflex 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 Zanaflex with alcohol and other CNS depressants (e.g., benzodiazepines, opioids, tricyclic antidepressants) may be additive. Monitor patients who take Zanaflex with another CNS depressant for symptoms of excess sedation. [ see Drug Interactions (7.5, 7.6) ]

5.4 Hallucinosis/Psychotic-Like Symptoms

Zanaflex 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 Zanaflex in patients who develop hallucinations.

5.5 Interaction with CYP1A2 Inhibitors

Because of potential drug interactions, Zanaflex 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 Zanaflex 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 Zanaflex 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

Zanaflex 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 Zanaflex 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

Zanaflex 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 to 28 mg 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 to 4 mg per day). [see Dosage and Administration (2.2)]

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 the clinical studies of another drug and may not reflect the rates observed in clinical practice.

Three double-blind, randomized, placebo controlled -clinical studies were conducted to evaluate the effect of tizanidine on spasticity control. Two studies were conducted in patients with multiple sclerosis and one in patients with spinal cord injury. Each study had a 13-week active treatment period which included a 3-week titration phase to the maximum tolerated dose up to 36 mg/day in three divided doses, a 9-week plateau phase where the dose of tizanidine was held constant and a 1-week dose tapering. In all, 264 patients received tizanidine and 261 patients received placebo. Across the three studies patient ages ranged from 15–69 years and 51.4 percent were women. The median dose during the plateau phase ranged from 20–28 mg/day.

The most frequent adverse reactions reported in multiple dose, placebo-controlled clinical studies involving 264 patients with spasticity were dry mouth, somnolence/sedation, asthenia (weakness, fatigue and/or tiredness) and dizziness. Three-quarters of the patients rated the events as mild to moderate and one-quarter of the patients rated the events as being severe. These events appeared to be dose related.

Table 1 lists signs and symptoms that were reported in greater than 2% of patients in three multiple dose, placebo-controlled studies who received Zanaflex where the frequency in the Zanaflex group was greater than the placebo group. For comparison purposes, the corresponding frequency of the event (per 100 patients) among placebo treated patients is also provided.

In the single dose, placebo-controlled study involving 142 patients with spasticity due to multiple sclerosis (Study 1) [see Clinical Studies (14)] , the patients were specifically asked if they had experienced any of the four most common adverse reactions: dry mouth, somnolence (drowsiness), asthenia (weakness, fatigue and/or tiredness) and dizziness. In addition, hypotension and bradycardia were observed. The occurrence of these reactions is summarized in Table 2. Other events were, in general, reported at a rate of 2% or less.

6.2 Post-Marketing Experience

The following adverse reactions have been identified during post approval use of Zanaflex. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

Certain events, such as somnolence, dry mouth, hypotension, decreased blood pressure, bradycardia, dizziness, weakness or asthenia, muscle spasms, hallucinations, fatigue, liver function test abnormality and hepatotoxicity, have been observed in post marketing and clinical trials and are discussed in previous sections of this document.

The following adverse reactions have been identified as occurring in the post marketing experience of Zanaflex. Based on the information provided regarding these reactions, a causal relationship with Zanaflex cannot be entirely excluded. The events are listed in order of decreasing clinical significance; severity in the post marketing setting is not reported.

• Stevens Johnson Syndrome
• Anaphylactic Reaction
• Exfoliative Dermatitis
• Ventricular Tachycardia
• Hepatitis
• Convulsion
• Depression
• Arthralgia
• Paresthesia
• Rash
• Tremor

7.1 Fluvoxamine

Concomitant use of fluvoxamine and Zanaflex 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 Zanaflex is contraindicated. Changes in pharmacokinetics of tizanidine when administered with ciprofloxacin resulted in significantly decreased blood pressure, increased drowsiness, and increased psychomotor impairment sSee Contraindications (4) and Clinical Pharmacology (12.3)]

7.3 CYP1A2 Inhibitors other than Fluvoxamine and Ciprofloxacin

Because of potential drug interactions, concomitant use of Zanaflex with other CYP1A2 inhibitors, such as zileuton, fluoroquinolones other than strong CYP1A2 inhibitors (which are contraindicated), antiarrythmics (amiodarone, mexiletine, propafenone, and verapamil), cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided. If their use is clinically necessary, therapy should be initiated with 2 mg dose and increased in 2–4 mg steps daily based on patient response to therapy. If adverse reactions such as hypotension, bradycardia, or excessive drowsiness occur, reduce or discontinue Zanaflex therapy. [ see Warnings and Precautions (5.5) and Clinical Pharmacology (12.3)]

7.4 Oral Contraceptives

Concomitant use of Zanaflex with oral contraceptives is not recommended. However, if concomitant use is clinically necessary, initiate Zanaflex with a single 2 mg dose and increase in 2–4 mg steps daily based on patient response to therapy. If adverse reactions such as hypotension, bradycardia, or excessive drowsiness occur, reduce or discontinue Zanaflex therapy. [ see Clinical Pharmacology (12.3)]

7.5 Alcohol

Alcohol increases the overall amount of drug in the bloodstream after a dose of Zanaflex. This was associated with an increase in adverse reactions of Zanaflex. The CNS depressant effects of Zanaflex and alcohol are additive. [ see Clinical Pharmacology (12.3)]

7.6 Other CNS Depressants

The sedative effects of Zanaflex with CNS depressants (e.g., benzodiazepines, opioids, tricyclic antidepressants) may be additive. Monitor patients who take Zanaflex with another CNS depressant for symptoms of excess sedation. [ see Clinical Pharmacology (12.3)]

7.7 α 2-adrenergic agonists

Because hypotensive effects may be cumulative, it is not recommended that Zanaflex be used with other α 2-adrenergic agonists. [ see Warnings and Precautions (5.1)]

8.1 Pregnancy

8.3 Nursing mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when Zanaflex is administered to a nursing woman.

8.4 Pediatric use

Safety and effectiveness in pediatric patients have not been established.

8.5 Geriatric use

Zanaflex is known to be substantially excreted by the kidney, and the risk of adverse reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.

Clinical studies of Zanaflex did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently than younger subjects. Cross-study comparison of pharmacokinetic data following single dose administration of 6 mg Zanaflex showed that younger subjects cleared the drug four times faster than the elderly subjects. In elderly patients with renal insufficiency (creatinine clearance <25 mL/min), tizanidine clearance is reduced by more than 50% compared to healthy elderly subjects; this would be expected to lead to a longer duration of clinical effect. During titration, the individual doses should be reduced. If higher doses are required, individual doses rather than dosing frequency should be increased. Monitor elderly patients because they may have an increased risk for adverse reactions associated with Zanaflex.

8.6 Impaired Renal Function

Zanaflex is known to be substantially excreted by the kidney, and the risk of adverse reactions to this drug may be greater in patients with impaired renal function. In patients with renal insufficiency (creatinine clearance < 25 mL/min) clearance was 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), Warnings and Precautions (5.7) and Clinical Pharmacology (12.3)]

8.7 Impaired Hepatic Function

The influence of hepatic impairment on the pharmacokinetics of tizanidine has not been evaluated. Because tizanidine is extensively metabolized in the liver, hepatic impairment would be expected to have significant effects on pharmacokinetics of tizanidine. [ see Dosing and Administration (2.3), Warnings and Precautions (5.2), and Clinical Pharmacology (12.3)].

9.2 Abuse

Abuse potential was not evaluated in human studies. Rats were able to distinguish tizanidine from saline in a standard discrimination paradigm, after training, but failed to generalize the effects of morphine, cocaine, diazepam, or phenobarbital to tizanidine.

9.3 Dependence

Tizanidine is closely related to clonidine, which is often abused in combination with narcotics and is known to cause symptoms of rebound upon abrupt withdrawal. Three cases of rebound symptoms on sudden withdrawal of tizanidine have been reported. The case reports suggest that these patients were also misusing narcotics. Withdrawal symptoms included hypertension, tachycardia, hypertonia, tremor, and anxiety. Withdrawal symptoms are more likely to occur in cases where high doses are used, especially for prolonged periods, or with concomitant use of narcotics. If therapy needs to be discontinued, the dose should be decreased slowly to minimize the risk of withdrawal symptoms [ see Dosage and Administration (2.2)].

Monkeys were shown to self-administer tizanidine in a dose-dependent manner, and abrupt cessation of tizanidine produced transient signs of withdrawal at doses > 35 times the maximum recommended human dose on a mg/m 2 basis. These transient withdrawal signs (increased locomotion, body twitching, and aversive behavior toward the observer) were not reversed by naloxone administration.

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

13.1 Carcinogenesis, mutagenesis, impairment of fertility

Single-Dose Study in Patients with Multiple Sclerosis with Spasticity

In Study 1, patients with multiple sclerosis were randomized to receive single oral doses of drug or placebo. Patients and assessors were blind to treatment assignment and efforts were made to reduce the likelihood that assessors would become aware indirectly of treatment assignment (e.g., they did not provide direct care to patients and were prohibited from asking questions about side effects). In all, 140 patients received placebo, 8 mg or 16 mg of Zanaflex.

Response was assessed by physical examination; muscle tone was rated on a 5 point scale (Ashworth score), with a score of 0 used to describe normal muscle tone. A score of 1 indicated a slight spastic catch while a score of 2 indicated more marked muscle resistance. A score of 3 was used to describe considerable increase in tone, making passive movement difficult. A muscle immobilized by spasticity was given a score of 4. Spasm counts were also collected.

Assessments were made at 1, 2, 3 and 6 hours after treatment. A statistically significant reduction of the Ashworth score for Zanaflex compared to placebo was detected at 1, 2 and 3 hours after treatment. Figure 2 below shows a comparison of the mean change in muscle tone from baseline as measured by the Ashworth scale. The greatest reduction in muscle tone was 1 to 2 hours after treatment. By 6 hours after treatment, muscle tone in the 8 and 16 mg Zanaflex groups was indistinguishable from muscle tone in placebo treated patients. Within a given patient, improvement in muscle tone was correlated with plasma concentration. Plasma concentrations were variable from patient to patient at a given dose. Although 16 mg produced a larger effect, adverse events including hypotension were more common and more severe than in the 8 mg group. There were no differences in the number of spasms occurring in each group.

Figure 2: Single Dose Study—Mean Change in Muscle Tone from Baseline as Measured by the Ashworth Scale ± 95% Confidence Interval (A Negative Ashworth Score Signifies an Improvement in Muscle Tone from Baseline)

Seven-Week Study in Patients with Spinal Cord Injury with Spasticity

In a 7-week study (Study 2), 118 patients with spasticity secondary to spinal cord injury were randomized to either placebo or Zanaflex. Steps similar to those taken in the first study were employed to ensure the integrity of blinding.

Patients were titrated over 3 weeks up to a maximum tolerated dose or 36 mg daily given in three unequal doses (e.g., 10 mg given in the morning and afternoon and 16 mg given at night). Patients were then maintained on their maximally tolerated dose for 4 additional weeks (i.e., maintenance phase). Throughout the maintenance phase, muscle tone was assessed on the Ashworth scale within a period of 2.5 hours following either the morning or afternoon dose. The number of daytime spasms was recorded daily by patients.

At endpoint (the protocol-specified time of outcome assessment), there was a statistically significant reduction in muscle tone and frequency of spasms in the Zanaflex treated group compared to placebo. The reduction in muscle tone was not associated with a reduction in muscle strength (a desirable outcome) but also did not lead to any consistent advantage of Zanaflex treated patients on measures of activities of daily living. Figure 3 below shows a comparison of the mean change in muscle tone from baseline as measured by the Ashworth scale.

Figure 3: Seven Week Study—Mean Change in Muscle Tone 0.5–2.5 Hours After Dosing as Measured by the Ashworth Scale ± 95% Confidence Interval (A Negative Ashworth Score Signifies an Improvement in Muscle Tone from Baseline)

16.1 Zanaflex Capsules®

Zanaflex Capsules ® (tizanidine hydrochloride) capsules are available in three strengths as two-piece hard gelatin capsules containing tizanidine hydrochloride 2.29 mg, 4.58 mg and 6.87 mg, equivalent to 2 mg, 4 mg and 6 mg tizanidine base.

• The 2 mg capsules have a light blue opaque body with a light blue opaque cap with "2 MG" printed on the cap: bottles of 150 capsules (NDC 10144-602-15)
• The 4 mg capsules have a white opaque body with a blue opaque cap with "4 MG" printed on the cap: bottles of 150 capsules (NDC 10144-604-15)
• The 6 mg capsules have a blue opaque body with a white stripe and blue opaque cap with "6 MG" printed on the capsules: bottles of 150 capsules (NDC 10144-606-15)

Store at 25°C (77°F); excursions permitted to 15–30°C (59–86°F) [see USP Controlled Room Temperature]. Dispense in containers with child resistant closure.

16.2 Zanaflex® Tablets

Zanaflex ® (tizanidine hydrochloride) tablets are available as 4 mg white, uncoated tablets containing tizanidine hydrochloride 4.58 mg, equivalent to 4 mg tizanidine base. The tablets have a quadrisecting score on one side and are debossed with "A594" on the other side. Tablets are provided as follows: bottles of 150 tablets (NDC 10144-594-15).

Store at 25°C (77°F); excursions permitted to 15–30°C (59–86°F) [see USP Controlled Room Temperature].

Dispense in containers with child resistant closure .

Serious Drug Interactions

Advise patients they should not take Zanaflex if they are taking fluvoxamine or ciprofloxacin because of the increased risk of serious adverse reactions including severe lowering of blood pressure and sedation. Instruct patients to inform their physicians or pharmacists when they start or stop taking any medication because of the risks associated with interaction between Zanaflex and other medicines.

Zanaflex Dosing

Tell patients to take Zanaflex exactly as prescribed (consistently either with or without food) and not to switch between tablets and capsules. Inform patients that they should not take more Zanaflex than prescribed because of the risk of adverse events at single doses greater than 8 mg or total daily doses greater than 36 mg. Tell patients that they should not suddenly discontinue Zanaflex, because rebound hypertension and tachycardia may occur.

Effects of Zanaflex

Warn patients that they may experience hypotension and to be careful when changing from a lying or sitting to a standing position. Tell patients that Zanaflex may cause them to become sedated or somnolent and they should be careful when performing activities that require alertness, such as driving a vehicle or operating machinery. Tell patients that the sedation may be additive when Zanaflex is taken in conjunction with drugs (baclofen, benzodiazepines) or substances (e.g., alcohol) that act as CNS depressants. Remind patients that if they depend on their spasticity to sustain posture and balance in locomotion, or whenever spasticity is utilized to obtain increased function, that Zanaflex decreases spasticity and caution should be used.