Tizanidine

Tizanidine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• dizziness
• drowsiness
• weakness
• nervousness
• depression
• vomiting
• tingling sensation in the arms, legs, hands, and feet
• dry mouth
• constipation
• diarrhea
• stomach pain
• heartburn
• increased muscle spasms
• back pain
• rash
• sweating

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately:

• nausea
• extreme tiredness
• unusual bleeding or bruising
• lack of energy
• loss of appetite
• pain in the upper right part of the stomach
• yellowing of the skin or eyes
• unexplained flu-like symptoms
• seeing things or hearing voices that do not exist
• slow heartbeat
• changes in vision

Tizanidine may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from excess heat and moisture (not in the bathroom).

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Dosage Forms & Strengths

tablet

• 2mg
• 4mg

capsule

• 2mg
• 4mg
• 6mg

Muscle Spasticity

Spasticity associated with multiple sclerosis and spinal cord injury

Initial: 2 mg PO q6-8hr PRN; no more than 3 doses q24hr

Maintenance: Titrate in 2-4 mg/day increments to optimum effect with minimum 1-4 days between dose increments

Not to exceed 36 mg/day; single doses >16 mg not studied

To discontinue taper gradually; decrease by 2-4 mg daily

Dosing Modifications

Renal impairment

• CrCl <25 mL/min: Use caution; clearance reduced >50%
• CrCl >25 mL/min: Not studied; use caution

Hepatic impairment

• Close monitoring of ADRs (eg, hypotension); avoid in severe impairment

Not recommended

Mechanism of Action

Alpha-2 adrenergic receptor agonist structurally related to clonidine; increases presynaptic inhibition of motor neurons

Absorption

Bioavailability: 40%

Peak serum time: 1-4 hr

Distribution

Protein bound: 30%

Vd: 2.4 L/kg

Metabolism

Extensively metabolized in the liver

Elimination

Half-life: 2.5 hr

Excretion: Feces (20%); urine (60%)

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.

Pharmacokinetics

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. Tizanidine is approximately 30% bound to plasma proteins.

Differences between Zanaflex Capsules® and Zanaflex® Tablets

Zanaflex Capsules® and Zanaflex® tablets are bioequivalent to each other under fasting conditions, but not under fed conditions. A single dose of either two 4 mg tablets or two 4 mg capsules was administered under fed and fasting conditions in an open label, four period, randomized crossover study in 96 human volunteers, of whom 81 were eligible for the statistical analysis. Following oral administration of either the tablet or capsule (in the fasted state), peak plasma concentrations of tizanidine occurred 1.0 hours after dosing with a half-life of approximately 2 hours. When two 4 mg tablets were administered with food, the mean maximal plasma concentration was increased by approximately 30%, and the median time to peak plasma concentration was increased by 25 minutes, to 1 hour and 25 minutes. In contrast, when two 4 mg capsules were administered with food, the mean maximal plasma concentration was decreased by 20%, the median time to peak plasma concentration was increased 2 to 3 hours. Consequently, the mean Cmax for the capsule when administered with food is approximately 66% the Cmax for the tablet when administered with food.

Food also increased the extent of absorption for both the tablets and capsules. The increase with the tablet (~30%) was significantly greater than with the capsule (~10%). Consequently when each was administered with food, the amount absorbed from the capsule was about 80% of the amount absorbed from the tablet. Administration of the capsule contents sprinkled on applesauce was not bioequivalent to administration of an intact capsule under fasting conditions. Administration of the capsule contents on applesauce resulted in a 15%–20% increase in Cmax and AUC of tizanidine and a 15 minute decrease in the median lag time and time to peak concentration compared to administration of an intact capsule while fasting.

Figure 1: Mean Tizanidine Concentration vs. Time Profiles For Zanaflex Tablets and Capsules (2 × 4 mg) Under Fasted and Fed Conditions

Tizanidine has linear pharmacokinetics over the doses studied in clinical development (1–20 mg). Tizanidine has a half-life of approximately 2.5 hours (CV=33%). Approximately 95% of an administered dose is metabolized. The primary cytochrome P450 isoenzyme involved in tizanidine metabolism is CYP1A2. Tizanidine metabolites are not known to be active; their half-lives range from 20 to 40 hours.

Following single and multiple oral dosing of 14C-tizanidine, an average of 60% and 20% of total radioactivity was recovered in the urine and feces, respectively.

Special Populations

No specific pharmacokinetic study was conducted to investigate age effects. 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. Zanaflex has not been evaluated in children. [see Use in Specific Populations]

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. Zanaflex is not recommended in this patient population [see Use in Specific Populations]

Tizanidine clearance is reduced by more than 50% in elderly patients with renal insufficiency (creatinine clearance < 25 mL/min) compared to healthy elderly subjects; this would be expected to lead to a longer duration of clinical effect. Zanaflex should be used with caution in renally impaired patients [see WARNINGS AND PRECAUTIONS and Use In Specific Populations].

No specific pharmacokinetic study was conducted to investigate gender effects. Retrospective analysis of pharmacokinetic data, however, following single and multiple dose administration of 4 mg Zanaflex showed that gender had no effect on the pharmacokinetics of tizanidine.

Pharmacokinetic differences due to race have not been studied.

Drug Interactions

The interaction between Zanaflex and either fluvoxamine or ciprofloxacin is most likely due to inhibition of CYP1A2 by fluvoxamine or ciprofloxacin. The effect of fluvoxamine on the pharmacokinetics of a single 4 mg dose of Zanaflex was studied in 10 healthy subjects. The Cmax, AUC, and half-life of tizanidine increased by 12- fold, 33-fold, and 3-fold, respectively. The effect of ciprofloxacin on the pharmacokinetics of a single 4 mg dose of Zanaflex was studied in 10 healthy subjects. The Cmax and AUC of tizanidine increased by 7-fold and 10-fold, respectively. [see CONTRAINDICATIONS]

Although there have been no clinical studies evaluating the effects of other CYP1A2 inhibitors on tizanidine, other CYP1A2 inhibitors, such as zileuton, other fluoroquinolones, antiarrythmics (amiodarone, mexiletine, propafenone and verapamil), cimetidine, famotidine oral contraceptives, acyclovir and ticlopidine, may also lead to substantial increases in tizanidine blood concentrations [see WARNINGS AND PRECAUTIONS].

In vitro studies of cytochrome P450 isoenzymes using human liver microsomes indicate that neither tizanidine nor the major metabolites are likely to affect the metabolism of other drugs metabolized by cytochrome P450 isoenzymes.

No specific pharmacokinetic study was conducted to investigate interaction between oral contraceptives and Zanaflex. Retrospective analysis of population pharmacokinetic data following single and multiple dose administration of 4 mg Zanaflex, however, showed that women concurrently taking oral contraceptives had 50% lower clearance of tizanidine compared to women not on oral contraceptives [see WARNINGS AND PRECAUTIONS].

Tizanidine delayed the Tmax of acetaminophen by 16 minutes. Acetaminophen did not affect the pharmacokinetics of tizanidine.

Alcohol increased the AUC of tizanidine by approximately 20%, while also increasing its Cmax by approximately 15%. This was associated with an increase in side effects of tizanidine. The CNS depressant effects of tizanidine and alcohol are additive.

Clinical Studies

Tizanidine's capacity to reduce increased muscle tone associated with spasticity was demonstrated in two adequate and well controlled studies in patients with multiple sclerosis or spinal cord injury (Studies 1 and 2).

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)

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)

• Chronic Pain
• Pain Management
• Pain Management Medication Types

Serious side effects have been reported with tizanidine. See the “Drug Precautions” section.

Common side effects of tizanidine include the following:

• dry mouth
• drowsiness
• weakness
• tiredness

This is not a complete list of tizanidine side effects. Ask your doctor or pharmacist for more information.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Before taking tizanidine, tell your doctor about all of your medical conditions. Especially tell your doctor if you:

• are allergic to tizanidine or to any of its ingredients
• have liver problems
• have kidney problems
• are pregnant or breastfeeding

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements.

Tizanidine is used to help relax certain muscles in your body. It relieves spasms, cramping, and tightness of the muscles caused by medical problems, such as multiple sclerosis or certain injuries to the spine. Tizanidine does not cure these problems, but it may allow other treatment, such as physical therapy, to be more helpful in improving your condition.

Tizanidine acts on the central nervous system (CNS) to produce its muscle relaxant effects. Its actions on the CNS may also cause some of the medicine's side effects.

tizanidine is available only with your doctor's prescription.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

• Chest pain or discomfort
• fever or chills
• nausea or vomiting
• nervousness
• pain or burning while urinating
• unusual tiredness

• Blurred vision
• flu-like symptoms
• irregular heartbeat
• itching skin
• kidney stones
• right upper stomach tenderness
• seeing things that are not there
• shortness of breath
• weight gain

• Continuing vomiting
• general feeling of tiredness or weakness
• headache
• light-colored stools

Get emergency help immediately if any of the following symptoms of overdose occur:

• Blurred vision
• change in consciousness
• chest pain or discomfort
• confusion
• decreased awareness or responsiveness
• difficult or troubled breathing
• dizziness, faintness or lightheadedness when getting up from a lying position
• irregular, fast or slow, or shallow breathing
• lightheadedness, dizziness, or fainting
• loss of consciousness
• pale or blue lips, fingernails, or skin
• severe sleepiness
• sleepiness or unusual drowsiness
• slow or irregular heartbeat
• sweating
• unusual tiredness or weakness

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

• Dizziness or lightheadedness, especially when getting up from a lying or sitting position
• drowsiness
• dry mouth
• fatigue
• sleepiness
• weakness

• Constipation
• nervousness
• sore throat

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Use this medicine as ordered by your doctor. Read all information given to you. Follow all instructions closely.

• Take with or without food. Always take with food or always take on an empty stomach.

What do I do if I miss a dose?

• If you take tizanidine on a regular basis, take a missed dose as soon as you think about it.
• If it is close to the time for your next dose, skip the missed dose and go back to your normal time.
• Do not take 2 doses at the same time or extra doses.
• Many times this medicine is taken on an as needed basis. Do not take more often than told by the doctor.

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
• Signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes.
• Signs of a urinary tract infection (UTI) like blood in the urine, burning or pain when passing urine, feeling the need to pass urine often or right away, fever, lower stomach pain, or pelvic pain.
• Very bad dizziness or passing out.
• Feeling confused.
• Hallucinations (seeing or hearing things that are not there).
• Mood changes.
• Change in the way you act.
• Slow heartbeat.
• Fever or chills.
• Sore throat.

• Store at room temperature.
• Protect from light.
• Store in a dry place. Do not store in a bathroom.
• Keep all drugs in a safe place. Keep all drugs out of the reach of children and pets.
• Check with your pharmacist about how to throw out unused drugs.

16.2 Tizanidine Tablets

Tizanidine Tablets USP, 2 mg are white to off white, oval, flat, beveled edged tablets debossed with “R179” on one side and “bisecting score” on other side. The tablets are available as follows:

50268-759-15 (10 tablets per card, 5 cards per carton)

Tizanidine Tablets USP, 4 mg are white to off white, oval, flat, beveled edged tablets debossed with “R180” on one side and “quadrisecting score” on other side. The tablets are available as follows:

  50268-760-15 (10 tablets per card, 5 cards per carton)

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

Dispensed in Unit Dose Package. For Institutional Use Only.

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Capsule, Oral:

Zanaflex: 2 mg, 4 mg, 6 mg

Generic: 2 mg, 4 mg, 6 mg

Tablet, Oral:

Zanaflex: 4 mg [scored]

Generic: 2 mg, 4 mg

You should not take tizanidine if you are also taking fluvoxamine (Luvox) or ciprofloxacin (Cipro).

Do not use tizanidine at a time when you need muscle tone for safe balance and movement during certain activities.

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

• a light-headed feeling, like you might pass out;

• weak or shallow breathing;

• confusion, hallucinations; or

• pain or burning when you urinate.

Common side effects may include:

• drowsiness, dizziness, weakness;

• feeling nervous;

• blurred vision;

• flu-like symptoms;

• dry mouth, trouble speaking;

• abnormal liver function tests;

• runny nose, sore throat;

• urination problems;

• vomiting, constipation; or

• uncontrolled muscle movements.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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