Methocarbamol (Robaxin)

(half-life 1–2 hours)

Mechanism unclear, likely CNS depressant. Less sedating than cyclobenzaprine and associated with decreased hospital length of stay in trauma patients with rib fractures.

  • Indication: Acute muscle spasm

  • Choose when: Want less sedation, safer in older adults

  • Start: 500–750 mg PO QID

  • Max: 4 g/day

  • Taper not needed

  • With or without food (take with food if stomach upset)

Tizanidine (Zanaflex)

(half-life 2–4 hours) (1–3 weeks; titrate; moderate sedation)

Alpha-2 adrenergic agonist that reduces spasticity by increasing presynaptic inhibition of motor neurons. Sedative properties may benefit patients with insomnia from muscle spasms.

  • Indication: Spasticity (MS, spinal cord injury), sometimes muscle spasm

  • Watch for: Hypotension, sedation, ↑ LFTs

  • Start: 2 mg PO at bedtime

  • Increase by 2–4 mg every 3–7 days as needed

  • If needed, up to 8 mg TID

  • Taper if >9 mg/day or long-term use

  • Decrease gradually over 1–2 weeks

  • With or without food (take with food if stomach upset)

Cyclobenzaprine (Flexeril)

(half-life ~18 hours) (nighttime only; moderate–high sedation)

Structurally similar to tricyclic antidepressants; acts on the brainstem to reduce tonic somatic motor activity.

  • Indication: Acute back/neck spasm

  • For young patients with acute muscle spasm

  • Avoid in: Elderly (anticholinergic effects), arrhythmia, glaucoma

  • Start: 5 mg PO TID

  • Titrate: Increase to 10 mg TID if needed

  • Duration: Short term (≤2–3 weeks)

  • Taper not needed

  • With or without food (take with food if stomach upset)

Metaxalone (Skelaxin)

(least sedating)

Short-term (1–2 weeks), ideal for daytime use.

  • Dosage: 800 mg PO 3–4 times/day (max 3.2 g/day)

  • Take with food to reduce GI upset

  • Higher cost and less generic availability, but increasingly used when sedation avoidance is prioritized

  • (MOA) remains incompletely understood but is attributed to general CNS depression

Baclofen

(half-life 3–4 hours) (2–4 weeks; taper)

GABA-B receptor agonist. More commonly used for spasticity from upper motor neuron syndromes but also indicated for musculoskeletal conditions; more for refractory cases.

  • Indication: Spasticity (MS, stroke, SCI)

  • Choose when: True neurologic spasticity

  • Warning: Abrupt discontinuation → seizures

  • ALWAYS taper over 1–2 weeks to avoid seizures, hallucinations, rebound spasticity

  • Start: 5 mg PO TID

  • Increase by 5 mg every 3 days as needed up to 20 mg TID

  • With or without food (take with food if stomach upset)

Notes

If one muscle relaxant fails after a full short-term course (e.g., 1–2 weeks), you can safely switch to another.

Complete the course + 3–7 day break to clear the drug and avoid overlapping sedation.

Try to limit to 3–4 discrete episodes per year.

Never overlap or combine due to additive CNS depression; elderly patients: max 1–2 episodes/year.

These medications are used for acute flares.

Chronic daily use (>3 months) risks tolerance, dependence, falls, and cognitive decline.


Quick Guide 

Indication: Acute muscle spasm (short-term use only 1–2 weeks).

Selection:
- Older adult → Methocarbamol or Metaxalone
- Needs daytime function → Metaxalone
- Spasm + insomnia → Tizanidine (night)
- Young acute strain → Cyclobenzaprine (short term)
- True neurologic spasticity → Baclofen

Dosing:
- Methocarbamol 500–750 mg QID (max 4 g/day)
- Tizanidine 2 mg HS → titrate (monitor BP/LFTs)
- Cyclobenzaprine 5 mg TID → 10 mg TID if needed
- Metaxalone 800 mg 3–4x/day
- Baclofen 5 mg TID → titrate (ALWAYS taper)

Safety:
- Do NOT combine muscle relaxants
- Avoid alcohol, opioids, benzos
- Limit to ≤3–4 episodes/year (elderly ≤2/year)
- Avoid chronic daily use (>3 months)