science

Tizanidine

Tizanidine is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Tizanidine rather than just read about it. In short: Tizanidine, sold under the brand names Zanaflex and Sirdalud among others, is an α2-adrenergic receptor agonist and muscle relaxant which is used to treat muscle spasticity due to spinal cord injury, multiple sclerosis, and spastic cerebral palsy. Its effectiveness appears to be similar to that of other muscle relaxants like baclofen or diazepam.

Key takeaways

Tizanidine belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Tizanidine to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Tizanidine from memory before moving on to harder problems.

Reference excerpt

Tizanidine, sold under the brand names Zanaflex and Sirdalud among others, is an α2-adrenergic receptor agonist and muscle relaxant which is used to treat muscle spasticity due to spinal cord injury, multiple sclerosis, and spastic cerebral palsy. Its effectiveness appears to be similar to that of other muscle relaxants like baclofen or diazepam. The drug is taken orally. Common side effects of tizanidine include sleepiness, dry mouth, asthenia, dizziness, low blood pressure, and low heart rate. Serious side effects may include dangerously low blood pressure, liver problems, and psychosis. It is unclear if use in pregnancy and breastfeeding is safe. The drug is an α2-adrenergic receptor agonist, but how it works is not entirely clear. Tizanidine was approved for medical use in the United States in 1996. It is available as a generic medication. In 2023, it was the 81st most commonly prescribed medication in the United States, with more than 8 million prescriptions.

Medical uses

Muscle spasticity Tizanidine is approved and used as a muscle relaxant to treat muscle spasticity. It has been found to be as effective as other muscle relaxants and is more tolerable than baclofen and diazepam. Due to its short elimination half-life and duration, tizanidine is generally taken once every 6 to 8 hours as needed, with a maximum of 3 doses per 24 hours.

Other uses Tizanidine may be used off-label in the treatment of insomnia and for certain other uses.

Available forms Tizanidine is available in the form of oral tablets and capsules.

Contraindications Contraindications of tizanidine include concomitant use with strong CYP1A2 inhibitors and known hypersensitivity to tizanidine or its excipients. Tizanidine is contraindicated with strong CYP1A2 inhibitors as these drugs profoundly increase tizanidine levels. Warnings and precautions for tizanidine include hypotension, liver injury, sedation, and hallucinations and psychotic-like symptoms.

Side effects The most common side effects of tizanidine (>10%) include somnolence, dry mouth, asthenia (including weakness, fatigue, and/or tiredness), dizziness, hypotension, and bradycardia. At doses of 8 to 16 mg, the rates of these side effects were 78–92% for somnolence, 76–88% for dry mouth, 67–78% for asthenia, 22–45% for dizziness, 16–33% for hypotension, and 2–10% for bradycardia. Additional side effects of tizanidine may include drowsiness, nervousness, confusion, hallucinations, strange dreams, depression, vomiting, constipation, diarrhea, stomach pain, heartburn, increased muscle spasms, back pain, rash, sweating, and tingling sensations in the arms, legs, hands, and feet. Tizanidine can cause withdrawal symptoms upon abrupt discontinuation and should be gradually tapered to avoid and minimize such symptoms. Withdrawal symptoms include rebound hypertension, tachycardia, hypertonia, tremor, and anxiety.

Overdose Symptoms of overdose with tizanidine have been reported to include lethargy, somnolence, bradycardia, hypotension, respiratory depression, agitation, confusion, vomiting, and coma.

Interactions Concomitant use of tizanidine and moderate or potent CYP1A2 inhibitors (such as zileuton, certain antiarrhythmics (amiodarone, mexiletine, propafenone, verapamil), cimetidine, famotidine, aciclovir, ticlopidine and oral contraceptives) is contraindicated. Concomitant use of tizanidine with fluvoxamine, a potent CYP1A2 inhibitor in humans, resulted in a 33-fold increase in the tizanidine AUC (plasma drug concentration-time curve). For this reason fluvoxamine and tizanidine should not be taken at the same time. Fluoroquinolone antibiotics such as moxifloxacin, levofloxacin, and ciprofloxacin should also be avoided due to an increased serum concentration of tizanidine when administered concomitantly. Tizanidine has the potential to interact with other central nervous system depressants. Alcohol should be avoided, particularly as it can upset the stomach. The CNS-depressant effects of tizanidine and alcohol are additive. Caution with the following interactions:

Antibiotics such as enoxacin, gatifloxacin, levofloxacin, lomefloxacin, moxifloxacin, ofloxacin, sparfloxacin, trovafloxacin, or norfloxacin; Blood pressure medications such as clonidine, guanabenz, guanfacine (Tenex), or methyldopa; Heart rhythm medications such as amiodarone (Cordarone, Pacerone), mexiletine (Mexitil), propafenone (Rhythmol), and verapamil (Calan, Covera, Isoptin).

Pharmacology

Pharmacodynamics

Tizanidine is an α2-adrenergic receptor agonist and is closely related to clonidine. It has approximately one-tenth to one-fifteenth of the blood pressure-lowering effect or potency of clonidine. The relation between the α2-adrenergic receptor agonism and spasmolytic action of tizanidine is still not fully understood.

Pharmacokinetics

Absorption Tizanidine is essentially completely absorbed with oral administration. The oral bioavailability of tizanidine is approximately 40%. It is subject to extensive first-pass metabolism and this is responsible for its incomplete bioavailability. The pharmacokinetics of tizanidine are linear across a dose range of 1 to 20 mg. The time to peak levels with tizanidine under fasting conditions is 1 hour and under fed conditions is 1.5 to 3 hours. The pharmacokinetics of tizanidine with oral tablet and capsule formulations are the same under fasting conditions but diverge and are non-equivalent under fed conditions. The pharmacokinetics of tizanidine also change when capsules are opened and it is sprinkled onto applesauce versus intact capsules.

Distribution Tizanidine is extensively distributed throughout the body. Its volume of distribution is 2.4 L/kg following intravenous injection. The drug's plasma protein binding is approximately 30%.

Metabolism More than 95% of a dose of tizanidine is metabolized. The primary cytochrome P450 enzyme involved in the metabolism of tizanidine is CYP1A2. Strong CYP3A4 inhibitors such as fluvoxamine and ciprofloxacin can increase tizanidine exposure by 10- to 33-fold, indicating the key involvement of CYP1A2 in the metabolism of the drug. The metabolites of tizanidine are thought to be inactive.

Elimination Tizanidine is eliminated 60% in urine and 20% in feces. Its elimination half-life is approximately 2.5 hours. The inactive metabolites of tizanidine have half-lives of 20 to 40 hours.

Chemistry

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Tizanidine

Start with the simplest possible case. Write down what Tizanidine claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Tizanidine before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Tizanidine ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Tizanidine

In research: Tizanidine appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Tizanidine in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Tizanidine is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alpha2-adrenergic agonists, Antihypertensive agents, Benzothiadiazoles, so understanding it makes those chapters shorter.
In everyday life: Look for Tizanidine outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Tizanidine in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Tizanidine means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Tizanidine out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Tizanidine in simple terms?

Why does Tizanidine matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Tizanidine?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Tizanidine.