Tizanidine: Effects in Spasticity and Muscle Tension

Tizanidine (brand names Sirdalud, Sirdalud MR and generics) is a centrally acting muscle relaxant from the group of imidazoline derivatives. It exerts its effect as an agonist at alpha 2 adrenoreceptors in the spinal cord, dampens polysynaptic reflexes, and thereby reduces spasticity-related increases in muscle tone. In Germany, tizanidine is approved for treating spasticity in neurological disorders and painful muscle tension. In clinical practice, it is prescribed especially for multiple sclerosis, post-stroke, spinal cord injury, and chronic painful muscle tension.

Tizanidine is considered a reasonable option for patients who do not tolerate baclofen or for whom baclofen is not sufficiently effective. Compared to baclofen, tizanidine produces less impact on peripheral skeletal muscle strength, which is valued in patients with mobility limitations. On the other hand, pronounced drowsiness, hypotension, and interaction potential via CYP1A2 must be carefully considered when combining with other medications.

Mechanism of Action

Tizanidine binds presynaptically to alpha 2 adrenoreceptors in the central nervous system, especially in the dorsal portion of the spinal cord. This reduces the release of excitatory amino acids such as glutamate and aspartate from presynaptic terminals. The result is inhibition of polysynaptic reflexes responsible for spasticity-induced increases in muscle tone. Unlike baclofen, which primarily stimulates GABA B receptors, tizanidine does not act directly at inhibitory synapses but dampens excitatory transmission.

The effect occurs rapidly, with maximum effects achieved approximately one to two hours after oral administration. The half-life is approximately two to four hours, which is why the usual dosing is distributed over three to four individual doses per day. An extended-release formulation offers a longer duration of action and once-daily dosing.

Metabolism occurs primarily hepatically via CYP1A2 to inactive metabolites, which are eliminated renally. CYP1A2 is genetically variable and is sensitive to inhibitors, which can lead to significant fluctuations in drug levels when multiple medications are used. Smoking also induces CYP1A2 and can reduce efficacy.

Indications

• Spasticity in Multiple Sclerosis, reduction in muscle tone with preserved muscle strength
• Spasticity after Stroke, particularly in the subacute rehabilitation phase
• Spasticity after Spinal Cord Injury, both tetraplegia and paraplegia
• Painful Muscle Tension, such as chronic back pain, used short-term and as a complement to physiotherapy
• Tension Headache and cervical syndrome as second-line therapy when other measures are ineffective

Tizanidine is not intended for acute treatment of severe spasticity in emergency settings. For life-threatening spasticity, other agents such as intravenous diazepam or intrathecal baclofen are used.

Dosage and Administration

Initiation: 2 mg three times daily or 4 mg at night. Gradual increase by 2 to 4 mg every three to seven days depending on efficacy and tolerability.

Maintenance Dose for Spasticity: Usually 12 to 24 mg per day divided into three to four individual doses. Maximum 36 mg per day.

Painful Muscle Tension: Short-term, 2 to 4 mg three times daily for a maximum of one week, then reassessment.

Extended-Release Form (MR): Once daily, starting with 6 mg, increase to 12 or 24 mg possible. Swallow extended-release capsule whole; contents can be dispersed on soft food.

Renal Impairment: With eGFR below 25 ml per minute, halve starting dose, slow titration. Hepatic Impairment: Use cautiously with impaired liver function, not recommended with severe impairment due to prolonged levels and hepatotoxicity risk.

Administration Notes: Taking with meals increases absorption. Avoid abrupt discontinuation as rebound phenomena with hypertension, tachycardia, and increased spasticity can occur. Taper over at least one week.

Side Effects

Very Common: Drowsiness, somnolence, dry mouth, dizziness, hypotension, weakness.

Common: Dazedness, nausea, digestive disturbances, bradycardia, sleep disturbances, hallucinations particularly at higher doses, muscle weakness, headache.

Occasional to Rare: Elevation of liver transaminases up to acute hepatitis, loss of consciousness, allergic skin reactions, visual disturbances, acute psychological symptoms.

Clinically Relevant: Hepatotoxicity, especially with higher doses and longer duration of therapy. Liver enzyme monitoring is recommended before therapy begins and regularly during the first six months. Patients should be informed about warning signs such as unusual fatigue, dark urine, pale stools, or jaundice.

Discontinuation Syndrome: Abrupt discontinuation can lead to rebound hypertension, tachycardia, and excessive spasticity, therefore gradual tapering is required.

Drug Interactions

• Strong CYP1A2 Inhibitors such as fluvoxamine and ciprofloxacin: extreme elevation of tizanidine levels with severe hypotension and sedation, contraindicated.
• Other CYP1A2 Inhibitors such as cimetidine, verapamil, atazanavir, ticlopidine, oral contraceptives: relevant elevation in levels, dose reduction or avoidance is reasonable.
• CYP1A2 Inducers such as rifampicin, phenytoin, carbamazepine, tobacco smoke: decreased levels, loss of efficacy possible.
• Antihypertensives, Diuretics, Antidepressants with Alpha Blockade: additive hypotension and syncope risk.
• Alcohol, Benzodiazepines, Z-Substances, Opioids: Enhanced central depression, respiratory depression possible.
• Tricyclics, Antipsychotics: Additive sedative effects, especially in elderly patients, fall risk.
• Methotrexate: Individual reports of increased MTX toxicity, caution with higher-dose methotrexate.

Special Notes

Pregnancy: Data limited. Use should only occur if the benefit to the mother outweighs the risk. For spasticity in pregnancy, physiotherapy and in individual cases other active substances after individual counseling are alternatives. Breastfeeding: Minimal transfer into breast milk, breastfeeding during therapy is generally not recommended.

Children and Adolescents: Limited data, use only in specialized centers.

Elderly Patients: Caution due to pronounced hypotension and fall risk, halve starting dose, slow titration.

Driving Ability: Often impaired during dose titration and when changing doses. Even in stable condition, individual patients may not be fit to drive; individual assessment is necessary.

Surgery and Anesthesia: Preoperative information for the anesthesia team, as additionally administered sedatives and muscle relaxants may have different effects.

Lifestyle: Tizanidine complements but does not replace non-pharmacological measures such as physiotherapy, assistive device provision, cognitive strategies, and in multiple sclerosis disease-modifying therapies.

You May Also Be Interested In

• Baclofen, GABA B agonist as an alternative muscle relaxant
• Methocarbamol, centrally acting muscle relaxant for muscle tension
• Tolperison, muscle relaxant for spasticity after stroke
• Clonidine, alpha 2 agonist with antihypertensive and sedative effects
• Pridinol, anticholinergic muscle relaxant for muscle tension

Frequently Asked Questions

Sources

• Gelbe Liste, Tizanidine Active Ingredient Profile
• BfArM, Federal Institute for Drugs and Medical Devices
• AWMF, Guidelines for Spasticity Therapy
• EMA, European Medicines Agency