Tizanidine

Zanaflex is indicated for spasticity in adults. Its brief therapeutic effect favors selected activities/times when relief is most needed. Supporting trials included multiple sclerosis and spinal cord injury; reduced muscle tone did not consistently translate to improved daily-function measures. Do not imply approval for every acute musculoskeletal pain syndrome.

Assess goals, useful residual tone, mobility, fall risk and sedative/antihypertensive therapy before treatment. Some patients rely on tone for standing or balance, so reduction can impair function. This focused profile covers selected oral tablets/capsules for adult spasticity; pediatric and off-label acute-pain protocols are outside scope. Tizanidine is not a controlled substance, but dependence/rebound can occur.

Start 2 mg by mouth every 6–8 hours as needed, at most three doses in 24 hours. Increase each dose by 2–4 mg at intervals of 1–4 days according to response/tolerability. Maximum total 36 mg/day; single doses >16 mg have not been studied. Do not mistake that study ceiling for a routine target—higher single doses produce more hypotension/sedation. Use only the prescribed activity-related doses.

May be taken with or without food, but consistently use the same relationship to meals and the prescribed form. Tablets/capsules are bioequivalent fasting, not fed. Food raises tablet exposure differently from capsules. Sprinkling capsule contents on applesauce also changes exposure versus the intact fasting capsule; do not open or switch without explicit prescribing/pharmacy instructions. Monitor response and adverse effects after any food/form change.

CrCl <25 mL/min or hepatic impairment: use lower individual doses while titrating. If higher doses are required, increase individual doses rather than frequency, guided by tolerability; no fixed percentage reduction is specified. Monitor closely for excessive sedation, dizziness, dry mouth, weakness and hypotension. Obtain aminotransferases at baseline and one month after the maximum dose is reached, or when injury is suspected.

The label recommends lowering total daily dosage by 2–4 mg per day when discontinuing, especially after high doses/prolonged use or with opioids, to limit rebound. Individualize with the clinician; do not suddenly stop regular therapy. This often-as-needed medicine should not be doubled to replace an omitted dose or compressed into shorter intervals; follow the prescribed schedule and discuss interruptions of chronic use.

Strong CYP1A2 inhibitors, including fluvoxamine and ciprofloxacin, are contraindicated. A history of hypersensitivity to tizanidine or the exact product’s ingredients is also contraindicated; anaphylaxis/angioedema have occurred. Other CYP1A2 inhibitors have avoidance/review recommendations, not the same blanket formal contraindication status.

No boxed warning appears in the selected current Zanaflex label. Significant interaction-related hypotension/sedation, liver injury, severe allergy and withdrawal warnings still require careful prescribing.

Common reported effects are dry mouth, somnolence/sedation, weakness/fatigue and dizziness; constipation, nausea/vomiting, liver-test changes and hypotension/bradycardia also occur. Serious postmarketing hepatic, allergic, skin, cardiac and neuropsychiatric reports cannot define incidence. Overdose can cause coma, respiratory depression, marked hypotension and bradycardia and may be fatal: emergency airway/cardiorespiratory support and Poison Help guidance (U.S. 1-800-222-1222). Dialysis is unlikely to remove tizanidine efficiently.

Human pregnancy data are inadequate; animal studies show developmental mortality/growth effects, so discuss maternal need and alternatives before or during pregnancy. Human milk/infant/milk-production data are absent, although animal milk transfer occurs; balance breastfeeding benefit with maternal need and possible infant risk. Human fertility data are inadequate; animal fertility effects do not establish a quantified human risk.

Pediatric safety/effectiveness is not established; no pediatric dose is supplied here. Older-adult trials were limited, and PK comparisons found slower clearance in older subjects. Review kidney function, start cautiously and monitor sedation, hypotension, falls and function; older adults with CrCl <25 need lower individual titration doses.

Clearance is reduced in severe renal insufficiency; in studied older patients with CrCl <25 it was more than 50% lower than healthy older subjects. Use lower doses and monitor rather than inferring an exact percentage dose conversion. Hepatic PK has not been evaluated, but extensive hepatic metabolism predicts important exposure changes; caution, lower doses and liver testing are recommended.

A central alpha₂ agonist thought to increase presynaptic inhibition of motor neurons, with effects greatest on polysynaptic pathways and reduced facilitation of spinal motor neurons. The same class activity contributes to hypotension and sedation.

Absorption

Essentially fully absorbed, but oral bioavailability ~40% from extensive first-pass metabolism. Fasting peak ~1 hour; food/form changes alter this.

Elimination

Parent half-life ~2–2.5 hours in studied conditions; ~95% metabolized, mainly by CYP1A2. Metabolites are not known to be active.

Excretion

Radiolabeled recovery ~60% in urine and ~20% in feces; this includes metabolites and is not 60% unchanged renal clearance.

Therapeutic timing

Peak tone reduction ~1–2 hours and effect wanes over several hours in trials; do not use PK averages to shorten the labeled 6–8-hour interval.

Follow spasticity relief, mobility/posture/balance, alertness, dizziness, blood pressure/pulse and falls, especially during titration or medicine changes. Review renal function in at-risk/older patients. Check aminotransferases at baseline, one month after maximum dose and if liver injury is suspected. Ask about hallucinations, sedatives, food/form consistency and withdrawal symptoms.

Take only the prescribed form/dose with a consistent meal pattern; tell every prescriber/pharmacist before starting or stopping a medicine. Avoid alcohol and hazardous activity until effects are known; rise slowly. Do not abruptly discontinue chronic use. Airway swelling, inability to wake, severe fainting or breathing impairment needs emergency care. Seek prompt review for jaundice, hallucinations or severe rebound symptoms.

Zanaflex 4 mg scored tablet is the representative product. Its current label covers tablets and 2/4/6 mg capsules; an Apotex tablet label separately verifies 2 mg and 4 mg generic tablets. Exact appearance/ingredients differ by manufacturer; use dispensing records rather than appearance alone.

Zanaflex: 20–25°C, excursions 15–30°C, child-resistant container. Selected Apotex tablets: same temperature range, tight light-resistant container. Keep securely away from children and follow the dispensed product’s instructions; do not apply capsule/food-handling assumptions to every generic product.