Zanaflex

Last reviewed on RxList: 1/4/2021
Zanaflex Side Effects Center

What Is Zanaflex?

Zanaflex (tizanidine hydrochloride) is a muscle relaxant used to treat muscle tightness and cramping (spasm) caused by conditions such as multiple sclerosis or spinal injury.

What Are Side Effects of Zanaflex?

Common side effects of Zanaflex may include:

  • anxiousness,
  • nervousness,
  • numbness or tingling,
  • stomach pain,
  • diarrhea,
  • constipation,
  • vomiting,
  • fever,
  • dry mouth,
  • drowsiness,
  • dizziness,
  • muscle weakness,
  • back pain,
  • increased muscle tone or spasms,
  • sweating,
  • skin rash, and
  • fatigue.

Dosage for Zanaflex

The recommended starting dose of Zanaflex is 2 mg. Dosage of Zanaflex 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.

What Drugs, Substances, or Supplements Interact with Zanaflex?

Zanaflex may interact with:

  • alcohol,
  • acyclovir,
  • cimetidine,
  • amotidine,
  • ticlopidine,
  • zileuton,
  • birth control pills,
  • antibiotics,
  • blood pressure medications, or
  • heart rhythm medications

Tell your doctor all medications and supplements you use.

Zanaflex During Pregnancy and Breastfeeding

Tell your doctor if you are pregnant or plan to become pregnant during treatment with Zanaflex; it may harm a fetus. It is unknown if Zanaflex passes into breast milk or if it could harm a nursing baby. Consult your doctor before breastfeeding.

Additional Information

Zanaflex may cause withdrawal reactions, especially if it has been used regularly for a long time or in high doses.

Our Zanaflex Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication.

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.

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Zanaflex Consumer Information

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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.

Read the entire detailed patient monograph for Zanaflex (Tizanidine)

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Zanaflex Professional Information

SIDE EFFECTS

The following adverse reactions are described elsewhere in other sections of the prescribing information:

  • Hypotension [see WARNINGS AND PRECAUTIONS]
  • Liver Injury [see WARNINGS AND PRECAUTIONS]
  • Sedation [see WARNINGS AND PRECAUTIONS]
  • Hallucinosis/Psychotic-Like Symptoms [see WARNINGS AND PRECAUTIONS]
  • Hypersensitivity Reactions [see WARNINGS AND PRECAUTIONS]

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.

Table 1: Multiple Dose, Placebo-Controlled Studies - Frequent (>2%) Adverse Reactions Reported for Which Zanaflex Tablets Incidence is Greater than Placebo

EventPlacebo
N = 261 %
Zanaflex Tablet
N = 264 %
Dry mouth1049
Somnolence1048
Asthenia*1641
Dizziness416
UTI710
Infection56
Constipation14
Liver test abnormality26
Vomiting03
Speech disorder03
Amblyopia (blurred vision)<13
Urinary frequency23
Flu syndrome23
Dyskinesia03
Nervousness<13
Pharyngitis13
Rhinitis23
*(weakness, fatigue, and/or tiredness)

In the single dose, placebo-controlled study involving 142 patients with spasticity due to multiple sclerosis (Study 1) [see Clinical Studies], 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.

Table 2: Single Dose, Placebo-Controlled Study - Common Adverse Reactions Reported

EventPlacebo
N = 48 %
Zanaflex Tablet, 8mg,
N = 45 %
Zanaflex Tablet, 16 mg,
N = 49 %
Somnolence317892
Dry mouth357688
Asthenia*406778
Dizziness42245
Hypotension01633
Bradycardia0210
*(weakness, fatigue, and/or tiredness)

Postmarketing 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

Read the entire FDA prescribing information for Zanaflex (Tizanidine)

© Zanaflex Patient Information is supplied by Cerner Multum, Inc. and Zanaflex Consumer information is supplied by First Databank, Inc., used under license and subject to their respective copyrights.

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