TIZANIDINE HYDROCHLORIDE

TIZANIDINE HYDROCHLORIDE
(ti-zan'i-deen)
Zanaflex
Classifications: skeletal muscle relaxant, central-acting;
Therapeutic:skeletal muscle relaxant, central-acting; antispasmodic
Prototype: Cyclobenzaprine
Pregnancy Category: C

Availability

4 mg tablets; 2 mg, 4 mg, 6 mg capsules

Action

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.

Therapeutic Effect

Site of action is the spinal cord; reduces skeletal muscle spasms. Effectiveness indicated by decreased muscle tone.

Uses

Acute and intermittent management of increased muscle tone associated with spasticity.

Contraindications

Hypersensitivity to tizanidine; pregnancy (category C). Safety in labor and delivery is unknown.

Cautious Use

Patients with hepatic impairment, hepatic disease; renal insufficiency (Cl_cr <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

Spasticity
Adult: PO Start with 4 mg and gradually increase to 8 mg q6–8h prn (max: 3 doses or 36 mg/24 h)

Renal Impairment
Cl_cr <25 mL/min: use lower dose

Administration

Oral

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.

Interactions

Drug: 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.

Pharmacokinetics

Absorption: Rapidly absorbed from GI tract; 40% bioavailability. Peak: 1–2 h. Duration: 3–6 h. Distribution: Crosses placenta, distributed into breast milk. Metabolism: In the liver. Elimination: 60% in urine, 20% in feces. Half-Life: 2.5 h.

Nursing Implications

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 thereafter.
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.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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