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Muscle Relaxant — Alpha-2 Agonist Pregnancy: Avoid — insufficient data

Tizanidine

Brand names: Zanaflex

Adult dose

Dose: 2 mg initially; titrate by 2 mg every 3–7 days; usual dose 6–12 mg/day in 3 divided doses
Route: Oral
Frequency: Three times daily
Max: 36 mg/day
Centrally acting alpha-2 agonist — inhibits spinal interneurons to reduce spasticity. Alternative to baclofen for spasticity in MS, spinal cord injury, and stroke. Less muscle weakness than baclofen. May cause significant sedation and hepatotoxicity — LFT monitoring mandatory.

Paediatric dose

Route:
Seek specialist opinion — limited paediatric data. Not licensed in children.

Dose adjustments

Renal

Avoid in renal impairment — active metabolites accumulate. If unavoidable, use lowest dose with close monitoring.

Hepatic

Contraindicated in hepatic impairment — hepatotoxicity risk; LFTs mandatory.

Clinical pearls

  • Ciprofloxacin and fluvoxamine are CONTRAINDICATED with tizanidine — commonly prescribed drugs that can cause fatal hypotension and CNS depression through CYP1A2 inhibition. Check interactions before prescribing.
  • LFT monitoring mandatory: at 1, 3, and 6 months; then every 6 months. Stop if ALT >3× ULN.
  • Abrupt withdrawal causes rebound hypertension and tachycardia — taper slowly over 1–2 weeks

Contraindications

  • Hepatic impairment
  • Concomitant fluvoxamine or ciprofloxacin (CYP1A2 inhibition — plasma levels increase 33× and 10× respectively — potentially fatal)

Side effects

  • Sedation (significant)
  • Dry mouth
  • Hypotension (especially postural)
  • Dizziness
  • Hepatotoxicity (LFT elevation in up to 5%)
  • Weakness
  • Hallucinations (high doses)

Interactions

  • Fluvoxamine (contraindicated — 33-fold increase in tizanidine levels)
  • Ciprofloxacin (contraindicated — 10-fold increase)
  • Other CYP1A2 inhibitors — amiodarone, mexiletine (increase levels)
  • Antihypertensives (additive hypotension)
  • Other CNS depressants (additive sedation)

Monitoring

  • LFTs at 1, 3, 6 months then 6-monthly
  • Blood pressure (postural hypotension)
  • Spasticity scales (MAS)
  • Sedation assessment

Reference: BNFc; BNF 90; NICE NG109 (Spasticity); MHRA Tizanidine Drug Interaction Warning; BNFc. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Pathways