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Tizanidine hydrochloride
Tizanidine hydrochloride (Zanaflex)
Tizanidine hydrochloride
(tye-ZAN-ih-deen)
Pregnancy Category: C Zanaflex (Rx)

Classification: Skeletal muscle relaxant, centrally-acting

See Also: See also Skeletal Muscle Relaxants, Centrally Acting.

Action/Kinetics: Acts on central þ-2 adrenergic receptors; reduces spasticity by increasing presynaptic inhibition of motor neurons possibly by reducing release of excitatory amino acids. Greatest effects are on polysynaptic pathways. Also may reduce postsynaptic excitatory transmitter activity, decrease the firing rate of noradrenergic locus ceruleas neurons, and inhibit synaptic transmission of nociceptive stimuli in the spinal pathways. Peak effect: 1-2 hr. Duration: 3-6 hr. Extensive first pass metabolism. t1/2: About 2.5 hr. Excreted in urine and feces. Elderly clear drug more slowly.

Uses: Acute and intermittent management of muscle spasticity.

Contraindications: Use with þ-2-adrenergic agonists.

Special Concerns: Use with caution in renal impairment, in elderly and during laction. Use with extreme caution in hepatic insufficiency. Safety and efficacy have not been determined in children.

Side Effects: Note: Side effects listed are those with a frequency of 0.1% or greater. CV: Hypotension, vasodilation, postural hypotension, syncope, migraine, arrhythmia. GI: Hepatotoxicity, dry mouth, constipation, pharyngitis, vomiting, abdominal pain, diarrhea, dyspepsia, dysphagia, cholelithiasis, fecal impaction, flatulence, GI hemorrhage hepatitis, melena. CNS: Dizziness, dyskinesia, nervousness, somnolence, sedation, hallucinations, psychotic-like symptoms, depression, anxiety, paresthesia, tremor, emotional lability, seizures, paralysis, abnormal thinking, vertigo, abnormal dreams, agitation, depersonalization, euphoria, stupor, dysautonomia, neuralgia. GU: Urinary frequency, UTI, urinary urgency, cystitis, menorrhagia, pyelonephritis, urinary retention, kidney calculus, enlarged uterine fibroids, vaginal moniliasis, vaginitis. Hematologic: Ecchymosis, anemia, leukopenia, leukocytosis. Musculoskeletal: Myasthenia, back pain, pathological fracture, arthralgia, arthritis, bursitis. Respiratory: Sinusitis, pneumonia, bronchitis, rhinitis. Dermatologic: Rash, sweating, skin ulcer, pruritus, dry skin, acne, alopecia, urticaria. Body as a whole: Flu syndrome, weight loss, infection, sepsis, cellulitis, death allergic reaction, moniliasis, malaise, asthenia, fever, abscess, edema. Ophthalmic: Glaucoma, amblyopia, conjunctivitis, eye pain, optic neuritis, retinal hemorrhage, visual field defect. Otic: Ear pain, tinnitus, deafness, otitis media. Miscellaneous: Speech disorder.

Laboratory Test Alterations: ALT. Abnormal LFTs. Hypercholesterolemia, hyperlipemia, hypothyroidism, adrenal cortical insufficiency, hyperglycemia, hypokalemia, hyponatremia, hypoproteinemia.

Drug Interactions: Alcohol / Tizanidine side effects; additive CNS depressant effects Alpha-2-adrenergic agonists / Additive hypotension Oral contraceptives / Tizanidine clearance

How Supplied: Tablets: 4 mg

Dosage
•Tablets Muscle spasticity.
Initial: 4 mg; then increase dose gradually in 2 to 4 mg steps to optimum effect. Dose can be repeated at 6-8-hr intervals, to maximum of 3 doses/24 hr, not to exceed 36 mg/day. There is no experience with repeated, single, daytime doses greater than 12 mg or total daily doses of 36 mg or more.