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Tizanidine (Zanaflex)

Muscle Relaxantprescriptionoral · inferred

Central alpha-2 adrenergic agonist that reduces spasticity by increasing presynaptic inhibition of motor neurons. Acts at both spinal and supraspinal levels. Structurally related to clonidine with similar but more selective antispastic effect. Short-acting, used PRN or TID. Bioavailability increases dramatically with food (Cmax increases 30%, AUC increases 20%). Extensively metabolized by CYP1A2, contraindicated with fluvoxamine and ciprofloxacin. Causes hypotension, sedation, and dry mouth.

Projected serum levels — 4 mg, once daily

Tizanidine (Zanaflex)
Tizanidine (Zanaflex) modeled serum levels, 4 mg once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 1 days. 0 0.50 1 1.5 2 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 1

Maintenance schedule: 4 mg once daily (oral).

Modeled steady state after ~1 days: peak ≈ 1.2 mg, trough ≈ 0.002 mg body load. Population-based estimate over 15 days for a 4 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Muscle Relaxant
Route modeled
Oral
Model confidence
inferred
Half-life
2.5 h
Common dose
4 mg
Suggested maximum
36 mg/day
Reference dose range
2–36 mg (single dose)
Suggested cadence
once daily
Validated against
4 mg oral — Cmax 0.005 mg/L at 1 h

Documented interactions

  • danger
    Apigenin + Tizanidine (Zanaflex) CYP inhibition

    Apigenin reversible_inhibitor of CYP1A2 predicted to change Tizanidine (Zanaflex) AUC by ~3.33x

  • danger
    Ciprofloxacin (Cipro) + Tizanidine (Zanaflex) CYP inhibition

    Ciprofloxacin (Cipro) reversible_inhibitor of CYP1A2 predicted to change Tizanidine (Zanaflex) AUC by ~3.33x

  • danger
    DIM (Diindolylmethane) + Tizanidine (Zanaflex) CYP induction

    DIM (Diindolylmethane) inducer of CYP1A2 predicted to change Tizanidine (Zanaflex) AUC by ~0.50x

  • danger
    Ethinyl Estradiol + Tizanidine (Zanaflex) CYP inhibition

    Ethinyl Estradiol reversible_inhibitor of CYP1A2 predicted to change Tizanidine (Zanaflex) AUC by ~3.33x

  • danger
    Fluvoxamine (Luvox) + Tizanidine (Zanaflex) CYP inhibition

    Fluvoxamine (Luvox) reversible_inhibitor of CYP1A2 predicted to change Tizanidine (Zanaflex) AUC by ~3.33x

  • danger
    Kava (Kavalactones) + Tizanidine (Zanaflex) CYP inhibition

    Kava (Kavalactones) reversible_inhibitor of CYP1A2 predicted to change Tizanidine (Zanaflex) AUC by ~3.33x

Serum checks 17 modeled interaction pairings for tizanidine (zanaflex) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. Tizanidine versus baclofen in the treatment of spasticity in patients with multiple sclerosis Bass B et al. · Canadian Journal of Neurological Sciences, 1988 DOI

    Double-blind crossover RCT demonstrating tizanidine was equally effective as baclofen for MS spasticity reduction, with less muscle weakness and better preservation of voluntary motor function.

  2. Pharmacokinetics and pharmacodynamics of tizanidine Wagstaff AJ, Bryson HM · Clinical Pharmacokinetics, 1997 DOI

    PK review establishing tizanidine half-life of 2.5 hours, 40% oral bioavailability, extensive CYP1A2 first-pass metabolism, and significant food-effect on absorption kinetics.

2 published studies referenced in the app, each with a plain-language summary.