Products
Tizanidine is commercially available in tablet and sustained-release capsule form (Sirdalud, Sirdalud MR, generics). It has been approved in many countries since 1983.
Structure and properties
Tizanidine (C9H8ClN5S, Mr = 253.7 g/mol) is present in drugs as tizanidine hydrochloride, a white crystalline powder that is somewhat soluble in water. It is an imidazoline and a benzothiodiazole and structurally related to antihypertensives such as clonidine, which explains its effects on blood pressure and heart rate.
Effects
Tizanidine (ATC M03BX02) has central muscle relaxant and anticonvulsant properties. The effects are thought to include agonism at presynaptic α2-adrenoreceptors, resulting in inhibition of the release of excitatory neurotransmitters.
Indications
Tizanidine is approved for the treatment of painful muscle spasms and spasticity resulting from multiple sclerosis, spinal cord injury, or brain injury.
Dosage
According to the drug label. Tizanidine is usually administered three to a maximum of four times daily because of its short half-life of two to four hours. For the sustained-release dosage forms, once-daily administration is sufficient.
Contraindications
- Hypersensitivity
- Sark impaired liver function
- Concurrent use with strong CYP1A2 inhibitors.
Full precautions can be found in the drug label.
Interactions
Tizanidine is biotransformed and inactivated by CYP1A2 and has a high first-pass metabolism. Therefore, it should not be co-administered with potent CYP1A2 inhibitors such as the antidepressant fluvoxamine or the antibiotic ciprofloxacin, because plasma levels may otherwise rise sharply, which may increase adverse effects and lead to QT interval prolongation. Antihypertensive drugs may cause low blood pressure and slow heartbeat, and centrally acting drugs and alcohol may increase adverse central effects.
Adverse effects
The most common adverse effects include drowsiness, fatigue, dizziness, dizziness, low pulse, low blood pressure, and dry mouth. Rarely, hallucinations, insomnia, sleep disturbances, digestive problems, elevation of liver enzymes, and muscle weakness have been reported. Very rarely, hepatitis and liver failure are possible.
