Zyflo, Zyflo CR
Classifications: bronchodilator (respiratory smooth muscle relaxant); leukotriene receptor antagonist;
Therapeutic: bronchodilator
; leukotriene receptor antagonist
Prototype: Zafirlukast
Pregnancy Category: C


600 mg tablets; 600 mg controlled release tablets


Inhibits 5-lipoxygenase, the enzyme needed to start the conversion of arachidonic acid to leukotrienes, which are important inflammatory agents that induce bronchoconstriction and mucus production.

Therapeutic Effect

Zileuton helps to prevent the signs and symptoms of asthma including airway edema, smooth muscle constriction, and altered cellular activity due to inflammation.


Prophylaxis and chronic treatment of asthma in adults and children <12 y.


Hypersensitivity to zileuton or zafirlukast, active liver disease, status asthmaticus; QT prolongation; lactation, pregnancy (category C).

Cautious Use

Hepatic insufficiency; alcoholism; older adults; older females; fever; infection; history of QT prolongation. Safety and effectiveness in children <12 y are not established.

Route & Dosage

Adult/Child (>12 y): PO 600 mg q.i.d. OR 2 controlled release tablets b.i.d.


  • Give at meals and bedtime.
  • Store at room temperature, 15°–30° C (59°–86° F); protect from light.

Adverse Effects (≥1%)

Body as a Whole: Pain, asthenia, myalgia, arthralgia, fever, malaise, neck pain/rigidity. CNS: Headache, dizziness, insomnia, nervousness, somnolence. CV: Chest pain. GI: Abdominal pain, dyspepsia, nausea, constipation, flatulence, vomiting, elevated liver function tests, asymptomatic hepatitis. Skin: Pruritus. Other: Conjunctivitis, hypertonia, lymphadenopathy, vaginitis, UTI, leukopenia.


Drug: May double theophylline levels and increase toxicity. Increases hypoprothrombinemic effects of warfarin. May increase levels of beta blockers (especially propranolol), leading to hypotension and bradycardia.


Absorption: Rapidly from GI tract. Peak: 1.7 h. Duration: 5–8 h. Distribution: 93% protein bound; secreted in the breast milk of rats. Metabolism: In liver primarily via glucuronide conjugation. Elimination: Primarily in urine (94%). Half-Life: 2.5 h.

Nursing Implications

Assessment & Drug Effects

  • Assess respiratory status and airway function regularly.
  • Lab tests: Periodic CBC and routine blood chemistry; monthly liver function tests for 3 mo, then every 2–3 mo for rest of first year, then periodically.
  • Instructions for CONCURRENT THERAPIES: Reduce theophylline dose and closely monitor theophylline levels; closely monitor PT and INR with warfarin therapy; closely monitor phenytoin level with phenytoin therapy; closely monitor HR and BP for excessive beta blockade with propranolol therapy.

Patient & Family Education

  • Take medication regularly even during symptom-free periods.
  • Drug is not intended to treat acute episodes of asthma.
  • Report to physician promptly S&S of hepatic toxicity (see Appendix F) or flu-like symptoms. Follow-up lab work is very important.
  • Notify physician if condition worsens while using prescribed doses of all antiasthmatic medications.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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