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tizanidine (Zanaflex)

Tradename: Zanaflex. Indications: - muscle spasms - skeletal muscle relaxant used for acute & intermittent management of increased muscle tone associated with spasticity - treatment of spasticity in patients with multiple sclerosis Contraindications: - concurrent use of alpha-2 adrenergic agonists Caution: 1) liver disease 2) renal disease 3) hypotension & patients receiving antihypertensive agents 4) cardiac disease Dosage: 1) adults: 4-12 mg TID 2) maximum of 3 doses in any 24 hour period with maximum daily dose of 36 mg/day 3) taper over 7 days when discontinued Reduce dosage in renal failure & hepatic insufficiency Tabs: 4 mg. Monitor: - liver function tests at 1, 3, & 6 months, then periodically [5] Adverse effects: 1) common (> 10%) - hypotension, sedation, daytime drowsiness, somnolence, xerostomia 2) less common (1-10%) - bradycardia, syncope, fatigue, dizziness, anxiety, nervousness, insomnia, pruritus, rash, nausea/vomiting,dyspepsia, constipation, diarrhea, abnormal liver function tests, muscle weakness, tremor 3) uncommon (< 1%) - palpitations, ventricular extrasystoles, psychosis, visual hallucinations, delusions, hepatic failure - tizanidine is associated with lower incidences of injury & delirium compared to baclofen when used for musculoskeletal pain [7] 4) withdrawal symptoms may occur with abrupt discontinuation - tachycardia, hypertonia [4] - rebound hypertension (less common than with clonidine) - NO rebound hypertension when tapered over 7 days 5) risk of falls < baclofen, cyclobenzaprine - risk of fracture = baclofen, cyclobenzaprine [8] Drug interactions: 1) oral contraceptives decrease tizanidine clearance 2) increased toxicity with concurrent use of: - diuretics, other alpha adrenergic agonists, antihypertensives, baclofen, alcohol & other CNS depressants 3) coadministration with CYP1A2 inhibitors (fluvoxamine or ciprofloxacin), increases serum concentration of tizanidine & potentiates its hypotensive & sedative effects Laboratory: - tizanidine in blood - tizanidine in serum/plasma Mechanism of action: 1) centrally-acting alpha-2 adrenergic agonist 2) pharmacologically similar to clonidine

Interactions

drug interactions drug adverse effects (more general classes)

General

alpha-2 adrenergic receptor agonist antispasmodic centrally-active alpha-adrenergic receptor agonist skeletal muscle relaxant (tranquilizer)

Properties

AGONIST-FOR: alpha-2 adrenergic receptor MISC-INFO: pregnancy-category D

Database Correlations

PUBCHEM correlations

References

  1. Kaiser Permanente Northern California Regional Drug Formulary, 1998
  2. Department of Veterans Affairs, VA National Formulary - restricted to spinal cord injury, neurology, & rehabilitation. should only be used in failed baclofen cases
  3. FDA Medwatch http://www.fda.gov/medwatch/safety/2007/safety07.htm#Zanaflex
  4. Prescriber's Letter 15(12): 2008 Common Oral Medications that May Need Tapering Detail-Document#: 241208 (subscription needed) http://www.prescribersletter.com
  5. Prescriber's Letter 17(7): 2010 Recommended Lab Monitoring for Common Medications Liver Function Test Scheduling Detail-Document#: 260704 (subscription needed) http://www.prescribersletter.com
  6. Deprecated Reference
  7. Su Zhang VR, Niu F, Lee EA et al Safety of baclofen versus tizanidine for older adults with musculoskeletal pain. J Am Geriatr Soc. 2023 Mar 29 PMID: 36989193
  8. Hwang YJ, Chang AR, Brotman DJ, Inker LA, Grams ME, Shin JI. Baclofen and the risk of fall and fracture in older adults: A real-world cohort study. J Am Geriatr Soc. 2023 Nov 7. PMID: 37933734 https://agsjournals.onlinelibrary.wiley.com/doi/abs/10.1111/jgs.18665