| TIZANIDINE HYDROCHLORIDE
Classifications: skeletal muscle relaxant, central-acting; Therapeutic:skeletal muscle relaxant, central-acting; antispasmodic
Pregnancy Category: C
4 mg tablets; 2 mg, 4 mg, 6 mg capsules
Centrally acting alpha-adrenergic agonist that reduces spasticity by increasing presynaptic inhibition of motor neurons.
Greatest effect on polysynaptic afferent reflex activity at the spinal cord level. No effect on skeletal muscle fibers, the
neuromuscular junction, or monosynaptic spinal reflexes.
Site of action is the spinal cord; reduces skeletal muscle spasms. Effectiveness indicated by decreased muscle tone.
Acute and intermittent management of increased muscle tone associated with spasticity.
Hypersensitivity to tizanidine; pregnancy (category C). Safety in labor and delivery is unknown.
Patients with hepatic impairment, hepatic disease; renal insufficiency (Clcr <25 mL/min), or renal failure; concurrent use of antihypertensive therapy; psychosis; women taking oral contraceptives;
older adults because of renal impairment; lactation. Safety and efficacy in children are not established.
Route & Dosage
Adult: PO Start with 4 mg and gradually increase to 8 mg q68h prn (max: 3 doses or 36 mg/24 h)
Clcr <25 mL/min: use lower dose
- Make dose increments gradually in 2- to 4-mg steps.
- Store at 15°30° C (59°86° F).
Adverse Effects (≥1%)Body as a Whole: Asthenia (tiredness),
flu-like syndrome, fever, myasthenia, back pain, infection. CNS: Somnolence, dizziness,
dyskinesia, nervousness, depression
, anxiety, paresthesia. CV: Hypotension, bradycardia. GI: Dry mouth, constipation
, abnormal liver function tests, vomiting, abdominal pain, diarrhea, dyspepsia. Respiratory:
Pharyngitis, rhinitis. Skin:
Rash, sweating, skin ulcer. Urogenital: UTI,
urinary frequency. Special Senses:
Speech disorder, blurred vision.
InteractionsDrug: oral contraceptives
decrease clearance of tizanidine. Alcohol
and other cns depressants
increase CNS depression
. Fluvoxamine, ciprofloxacin
increase tizanidine levels and toxicity. Herbal: Kava, valerian
may potentiate sedation.
Rapidly absorbed from GI tract; 40% bioavailability. Peak:
12 h. Duration:
36 h. Distribution:
Crosses placenta, distributed into breast milk. Metabolism:
In the liver. Elimination:
60% in urine, 20% in feces. Half-Life:
Assessment & Drug Effects
- Lab tests: Monitor liver function tests (AST, ALT) during the first 6 mo of treatment (baseline, 1, 3, and 6 mo) and periodically
- Monitor cardiovascular status and report orthostatic hypotension or bradycardia.
- Monitor closely older adults, those with renal impairment, and women taking oral contraceptives for adverse effects because
drug clearance is reduced.
Patient & Family Education
- Exercise caution with potentially hazardous activities requiring alertness since sedation is a common adverse effect. Effects
are additive with alcohol or other CNS depressants.
- Make position changes slowly because of the risk of orthostatic hypotension.
- Report unusual sensory experiences; hallucinations and delusions have occurred with tizanidine use.