Also Known As: Zileuton, Zyflo

Zileuton (trade name ZYFLO) is an orally active inhibitor of 5-lipoxygenase, and thus inhibits leukotrienes (LTB4, LTC4, LTD4, and LTE4) formation. Zileuton is used for the maintenance treatment of asthma. Zileuton was introduced in 1996 by Abbott Laboratories and is now marketed in two formulations by Cornerstone Therapeutics Inc. under the brand names ZYFLO and ZYFLO CR. The original immediate-release formulation of zileuton, known as ZYFLO, is taken four times per day. The extended-release formulation, ZYFLO CR, is taken twice daily.

Although the extended release formulation of zileuton is still available (Zyflo CR), the immediate release tablet was withdrawn from the U.S. market on February 12, 2008.

Zileuton is indicated for the prophylaxis and chronic treatment of asthma in adults and children 12 years of age and older. Zileuton is not indicated for use in the reversal of bronchospasm in acute asthma attacks. Therapy with zileuton can be continued during acute exacerbations of asthma.

The recommended dose of ZYFLO is one 600 mg tablet, four times per day. The tablets may be split in half to make them easier to swallow. The recommended dose of ZYFLO CR is two 600 mg extended-release tablets twice daily, within one hour after morning and evening meals, for a daily dose of 2400 mg. Do not split ZYFLO CR tablets in half.

Related compounds include montelukast (Singulair) and zafirlukast (Accolate). These two compounds are leukotriene receptor antagonists which block the action of specific leukotrienes, while zileuton inhibits leukotriene formation.

Research on mice suggests that Zileuton used alone or in combination with imatinib may inhibit chronic myeloid leukemia (CML).[3]

Contraindications and warnings

The most serious side effect of ZYFLO and ZYFLO CR is a potential elevation of liver enzymes (in 2% of patients). Therefore, zileuton is contraindicated in patients with active liver disease or persistent hepatic function enzymes elevations greater than three times the upper limit of normal. Hepatic function should be assessed prior to initiating ZYFLO CR, monthly for the first 3 months, every 2–3 months for the remainder of the first year, and periodically thereafter.

Neuropsychiatric events, including sleep disorders and behavioral changes, may occur with ZYFLO and ZYFLO CR. Patients should be instructed to notify their healthcare provider if neuropsychiatric events occur while using ZYFLO or ZYFLO CR.

Zileuton is a weak inhibitor of CYP1A2[4] and thus has three clinically important drug interactions, which include increasing warfarin, theophylline, and propranolol levels. It has been shown to lower theophylline clearance significantly, doubling the AUC and prolonging half-life by nearly 25%. Because of theophylline's relation to caffeine (both being a methylxanthine, and theophylline being a metabolite of caffeine), caffeine's metabolism and clearance may also be reduced, but there are no drug interaction studies between zileuton and caffeine.[5] The R-isomer of warfarin metabolism and clearance is mainly affected by zileuton, while the S-isomer is not (because of metabolism via different enzymes). This can lead to an increase in prothrombin time.[6]

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