Tizanidine

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DRUGS
Tizanidine

Tizanidine is a central alpha 2-adrenergic agonist. It is a short-acting muscle relaxant for the management of spasticity by temporarily relaxing the muscle tones. It works by blocking nerve impulses that are sent to the brain. The effects of tizanidine are greatest on polysynaptic pathways.

Introduction

Tizanidine is a central alpha 2-adrenergic agonist. It is a short-acting muscle relaxant for the management of spasticity by temporarily relaxing the muscle tones. It works by blocking nerve impulses that are sent to the brain. The effects of tizanidine are greatest on polysynaptic pathways.

 Pharmacological class: Muscle Relaxant

Indications

  • Muscle spasms

Pharamcological Action

Tizanidine is a short-acting muscle relaxant. It acts by reducing the spasticity by increasing the presynaptic inhibition of motor neurons through agonist action at 2-adrenergic receptor sites. The overall effect of these actions is thought to reduce the facilitation of spinal motor neurons. The effects of tizanidine are greatest on polysynaptic pathways.

Dosage

Muscle spasms: 4 mg orally every 6 to 8 hours

Pharmacokinetics

Tizanidine is completely absorbed following oral administration due to extensive first-pass hepatic metabolism. It 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. Approximately 95% of an administered dose is metabolized. The primary cytochrome P450 isoenzyme involved in tizanidine metabolism is CYP1A2. An average of 60% and 20% of total radioactivity was recovered in the urine and feces, respectively.

Contraindications

  • Contraindicated in patients taking potent inhibitors of CYP1A2, such as fluvoxamine or ciprofloxacin.

Drug Interactions

  • Concomitant intake of tizanidine and amiloride may have additive effects in lowering blood pressure.
  • Concomitant use of ciprofoxacin and tizanidine results in decreased blood pressure, increased drowsiness, and increased psychomotor impairment.
  • when administered with alcohol, it may increase the overall amount of drug & frequency of adverse reactions.
  • Concomitant use of tizanidine with CNS depressants may be additive as excess sedation may result.

Side effects

Common (affecting between 1 in10 to 1 in 100)

  • Fever or chills
  • Chest pain
  • Nausea and vomiting
  • Nervousness
  • Pain or burning while urinating
  • Tiredness

Uncommon (affecting 1 in 100 to 1 in 1000)

  • Flu-like symptoms
  • Blurred vision
  • Irregular heartbeat
  • Itching skin
  • Kidney stones
  • Right upper stomach tenderness
  • Shortness of breath
  • Weight gain

Very rare (affecting less than 1 in 10,000)

  • Hepatic failure
  • Hallucinations
  • Insomnia
  • Sleep disorders
  • Muscular weakness

Precautions

  • Avoid in patients who are allergic to tizanidine.
  • Avoid in patients taking ciprofloxacin or fluvoxamine
  • Avoid in patients who have or have ever had kidney or liver disease.
  • Do not drive or use machinery, as tizanidine can cause dizziness.
  • Avoid alcohol, as it can add to the drowsiness caused by tizanidine.

Clinic Evidence

  • In a study, tizanidine has been shown to be effective in reducing spasticity secondary to multiple sclerosis. The multicenter study assessed the efficacy and safety of oral tizanidine in patients who had spinal cord injury of > 12-month duration. Out of 124 patients in the study, 78 completed it. Muscle tone, assessed by Ashworth score, was significantly reduced (p = 0.0001) by tizanidine treatment in comparison with placebo.1

References

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