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Tizanidine

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Collated from PsychonautWiki, Pharmacology, DrugCentral, DailyMed. Where sources differ (e.g. dosing), Compare shows them side by side.

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Oral

Route dataPsychonautWiki

Dose
WeakerStronger
ThresholdLightCommonStrongHeavy
25 μg2–3 μg4–5 μg6–8 μg8 μg+
025 μg
LightCommonStrongHeavy
Duration
ShorterLonger
Onset15–45 minutes
Peak60–120 minutes
Total2–6 hours
OnsetCome-upPeakOffset

Dangerous interactionsPW

DepressantsDissociatives

Caution / uncertainPW

Stimulants

🧬 Receptor activityDC

TargetActionAffinitySource
Alpha-2A adrenergic receptor (ADRA2A)Agonist7.07 EC50DRUGCENTRAL
Alpha-2B adrenergic receptor (ADRA2B)Agonist—DRUGCENTRAL
Alpha-2C adrenergic receptor (ADRA2C)Agonist5.91 EC50DRUGCENTRAL
Alpha-1A adrenergic receptor (ADRA1A)—6.58 EC50DRUGCENTRAL
Alpha-1B adrenergic receptor—6.49 EC50DRUGCENTRAL
Nischarin (NISCH)—7.55 KiDRUGCENTRAL
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Mechanism of actionPHDM

Tizanidine reduces spasticity by causing presynaptic inhibition of motor neurons via agonist actions at Alpha-2 adrenergic receptor sites. This drug is centrally acting and leads to a reduction in the release of excitatory amino acids like glutamate and aspartate, which cause neuronal firing that leads to muscle spasm. The above reduction and excitatory neurotransmitter release results in presynaptic inhibition of motor neurons. The strongest effect of tizanidine has been shown to occur on spinal polysynaptic pathways. The anti-nociceptive and anticonvulsant activities of tizanidine may also be attributed to agonist action on Alpha-2 receptors. Tizanidine also binds with weaker affinity to the Alpha-1 receptors, explaining its slight and temporary effect on the cardiovascular system.

PharmacodynamicsPH

**A note on spasticity** Spasticity is an increase in muscle accompanied by uncontrolled, repetitive contractions of skeletal muscles which are involuntary. The patient suffering from muscle spasticity may have reduced mobility and high levels of pain, contributing to poor quality of life and problems performing activities of personal hygiene and care. **General effects** Tizanidine is a rapidly acting drug used for the relief of muscle spasticity when it is required for performing specific activities. It acts as an agonist at Alpha-2 adrenergic receptor sites and relieves symptoms of muscle spasticity, allowing the continuation of normal daily activities. In animal models, tizanidine has not been shown to exert direct effects on skeletal muscle fibers or the neuromuscular junction, and has shown no significant effect on monosynaptic spinal reflexes (consisting of the communication between only 1 sensory neuron and 1 motor neuron). The frequency of muscle spasm and clonus are shown to be decreased by tizanidine. Tizanidine shows a stronger action on polysynaptic reflexes, which involve several interneurons (relay neurons) communicating with motor neurons stimulating muscle movement. **Effects on blood pressure and heart rate** This drug decreases heart rate and blood pressure in humans. Despite this, rebound hypertension and tachycardia along with increased spasticity can occur when tizanidine is abruptly discontinued.

Pharmacokinetics

Half-lifePH

Approximately 2.5 hours.

AbsorptionPHDM

This drug undergoes significant first-pass metabolism. After the administration of an oral dose, tizanidine is mostly absorbed. The absolute oral bioavailability of tizanidine is measured to be about 40%. **Effect of food on absorption** Food has been shown to increase absorption for both the tablets and capsules. The increase in absorption with the tablet (about 30%) was noticeably higher than the capsule (~10%). When the capsule and tablet were administered with food, the amount absorbed from the capsule was about 80% of the amount absorbed from the tablet. It is therefore advisable to take this drug with food for increased absorption, especially in tablet form.
This drug is mainly eliminated by the kidney.
Extensively distributed throughout the body. The average steady-state volume of distribution is 2.4 L/kg.
**A note on renal impairment** Tizanidine clearance is found to be decreased 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. This drug should be used with caution in patients with renal impairment.

MetabolismPH

About 95% of the ingested dose of tizanidine is metabolized. The main enzyme involved in the hepatic metabolism of tizanidine is CYP1A2.
Tizanidine has known human metabolites that include 2-[(5-chloro-2,1,3-benzothiadiazol-4-yl)amino]-4,5-dihydro-1H-imidazol-4-ol.
Route of Elimination: Approximately 95% of an administered dose is metabolized.
Half Life: 2.5 hours

Protein bindingPH

About 30% bound to plasma proteins.

Plan when to take Tizanidine — see where onset, peak and comedown land on the clock

Fact-sheets from PsychonautWiki. Harm-reduction reference only — not medical advice.