Zyflo CR

Zyflo CR is part of the drug class:

• Leukotriene receptor antagonists

Medications can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of Zyflo CR, there are no specific foods that you must exclude from your diet when receiving this medication. 

Before taking Zyflo CR, tell your doctor about all of your medical conditions. Especially tell your doctor if you:

• are allergic to Zyflo CR or to any of its ingredients 
• drink alcohol
• have trouble swallowing pills
• have liver problems
• are pregnant or plan to become pregnant
• are breastfeeding or plan to breastfeed

​Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. 

If you take too much of Zyflo CR, call your healthcare provider or local Poison Control Center, or seek emergency medical attention right away.

Zileuton is a leukotriene (loo-koe-TRY-een) inhibitor. Leukotrienes are chemicals your body releases when you breathe in an allergen (such as pollen). These chemicals cause swelling in your lungs and tightening of the muscles around your airways, which can result in asthma symptoms.

Zileuton is used to prevent asthma attacks in adults and children as young as 12 years old.

Zileuton may also be used for purposes not listed in this medication guide.

Take the missed dose as soon as you remember. Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

• It is used to treat or prevent asthma.
• Do not use Zyflo CR (zileuton extended-release tablets) to treat an asthma attack. Use a rescue inhaler. Talk with your doctor.

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Headache.
• Upset stomach.
• Nose or throat irritation.
• Signs of a common cold.
• Muscle pain.
• Loose stools (diarrhea).

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-FDA-1088. You may also report side effects at http://www.fda.gov/medwatch.

The recommended dosage of Zyflo CR for the treatment of patients with asthma is two 600 mg extended-release tablets twice daily, within one hour after morning and evening meals, for a total daily dose of 2400 mg. Tablets should not be chewed, cut or crushed. If a dose is missed, the patient should take the next dose at the scheduled time and not double the dose. Assess hepatic function enzymes prior to initiation of Zyflo CR and periodically during treatment [see Contraindications (4), Warnings and Precautions (5), and Use in Specific Populations (8.7)].

Hepatotoxicity

Elevations of one or more hepatic function enzymes and bilirubin may occur during Zyflo CR therapy. These laboratory abnormalities may progress to clinically significant liver injury, remain unchanged, or resolve with continued treatment, usually within three weeks. The ALT (SGPT) test is considered the most sensitive indicator of liver injury for Zyflo CR.

Assess hepatic function enzymes prior to initiation of, and during therapy with, Zyflo CR. Assess serum ALT before treatment begins, once a month for the first 3 months, every 2-3 months for the remainder of the first year, and periodically thereafter for patients receiving long-term Zyflo CR therapy. If clinical signs and/or symptoms of liver dysfunction develop (e.g., right upper quadrant pain, nausea, fatigue, lethargy, pruritus, jaundice, or "flu-like" symptoms) or transaminase elevations ≥5×ULN occur, discontinue Zyflo CR and follow hepatic function enzymes until normal.

In controlled and open-label clinical studies involving more than 5000 patients treated with zileuton immediate-release tablets, the overall rate of ALT elevation ≥3×ULN was 3.2%. In these trials, one patient developed symptomatic hepatitis with jaundice, which resolved upon discontinuation of therapy. An additional 3 patients with transaminase elevations developed mild hyperbilirubinemia that was less than 3×ULN. There was no evidence of hypersensitivity or other alternative etiologies for these findings.

Since treatment with Zyflo CR may result in increased hepatic function enzymes and liver injury, Zyflo CR should be used with caution in patients who consume substantial quantities of alcohol and/or have a past history of liver disease.

Neuropsychiatric Events

Neuropsychiatric events have been reported in adult and adolescent patients taking zileuton, the active ingredient in Zyflo CR and zileuton immediate-release tablets.  Post-marketing reports with zileuton include sleep disorders and behavior changes.  The clinical details of some post-marketing reports involving zileuton appear consistent with a drug-induced effect.  Patients and prescribers should be alert for neuropsychiatric events.  Patients should be instructed to notify their prescriber if these changes occur.  Prescribers should carefully evaluate the risks and benefits of continuing treatment with Zyflo CR if such events occur [see Adverse Reactions (6.3)].

Zileuton is an orally active inhibitor of 5-lipoxygenase, the enzyme that catalyzes the formation of leukotrienes from arachidonic acid. Zileuton has the chemical name (±)-1-(1-Benzo[b]thien-2-ylethyl)-1-hydroxyurea and the following chemical structure:

zileuton

Zyflo CR (zileuton) extended-release tablets for oral administration are triple-layer tablets comprised of an immediate-release layer, a middle (barrier) layer, and an extended-release layer. Zyflo CR tablets are oblong, film-coated tablets with one red layer between two white layers, debossed on one side with "CT2". Each tablet contains 600 mg of zileuton and the following inactive ingredients: crospovidone, ferric oxide, glyceryl behenate, hydroxypropyl cellulose, hypromellose, magnesium stearate, mannitol, microcrystalline cellulose, povidone, pregelatinized starch, propylene glycol, sodium starch glycolate, and talc.

Mechanism of Action

Zileuton is an inhibitor of 5-lipoxygenase and thus inhibits leukotriene (LTB4, LTC4, LTD4 and LTE4) formation. Both the R(+) and S(-) enantiomers are pharmacologically active as 5-lipoxygenase inhibitors in in vitro and in vivo systems. Leukotrienes are substances that induce numerous biological effects including augmentation of neutrophil and eosinophil migration, neutrophil and monocyte aggregation, leukocyte adhesion, increased capillary permeability, and smooth muscle contraction. These effects contribute to inflammation, edema, mucus secretion, and bronchoconstriction in the airways of asthmatic patients. LTB4, a chemoattractant for neutrophils and eosinophils, and cysteinyl leukotrienes (LTC4, LTD4, LTE4) can be measured in a number of biological fluids including bronchoalveolar lavage fluid (BALF), blood, urine and sputum from asthmatic patients.

Zileuton is an orally active inhibitor of ex vivo LTB4 formation in several species, including mice, rats, rabbits, dogs, sheep, and monkeys. Zileuton inhibits arachidonic acid-induced ear edema in mice, neutrophil migration in mice in response to polyacrylamide gel, and eosinophil migration into the lungs of antigen-challenged sheep. In a mouse model of allergic inflammation, zileuton inhibited neutrophil and eosinophil influx, reduced the levels of multiple cytokines in the BALF, and reduced serum IgE levels. Zileuton inhibits leukotriene-dependent smooth muscle contractions in vitro in guinea pig and human airways. The compound inhibits leukotriene-dependent bronchospasm in antigen and arachidonic acid-challenged guinea pigs. In antigen-challenged sheep, zileuton inhibits late-phase bronchoconstriction and airway hyperreactivity. The clinical relevance of these findings is unknown.

Pharmacodynamics

Zileuton is an orally active inhibitor of ex vivo LTB4 formation in humans. The inhibition of LTB4 formation in whole blood is directly related to zileuton plasma levels. In patients with asthma, the IC50 is estimated to be 0.46 µg/mL, and maximum inhibition ≥80% is reached at a zileuton concentration of 2 µg/mL. In patients with asthma receiving zileuton immediate-release tablets 600 mg four times daily, peak plasma levels averaging 5.9 µg/mL were associated with a mean LTB4 inhibition of 98%. Zileuton inhibits the synthesis of cysteinyl leukotrienes as demonstrated by reduced urinary LTE4 levels.

Pharmacokinetics

Information on the pharmacokinetics of zileuton following the administration of zileuton immediate-release tablets is available in healthy subjects. The results of two clinical pharmacology studies using Zyflo CR are described below.

Absorption

A three-way crossover study was conducted in healthy male and female subjects (n=23) with a mean age of 33 (range 20-55) following single dose of 1200 mg (2 × 600 mg) Zyflo CR tablets under fasted and fed conditions, and two doses of 600 mg zileuton immediate-release tablets every 6 hours under fasted conditions. Food increased the peak mean plasma concentrations (Cmax) and the mean extent of absorption (AUC) of Zyflo CR by 18 and 34%, respectively, and prolonged Tmax from 2.1 hours to 4.3 hours. The relative bioavailability of Zyflo CR to zileuton immediate-release tablets with respect to Cmax and AUC under fasted conditions were 0.39 (90% CI: 0.36, 0.43) and 0.57 (90% CI: 0.52, 0.62), respectively. Similarly, relative bioavailability of Zyflo CR to zileuton immediate-release tablets with respect to Cmax and AUC under fed conditions were 0.45 (90% CI: 0.41, 0.49) and 0.76 (90% CI: 0.70, 0.83), respectively.

A three-way crossover study was conducted in healthy male and female subjects (n=24) with a mean age of 35 (range 19-56) following multiple doses of 1200 mg (2 × 600 mg) Zyflo CR tablets administered every 12 hours under fasted and fed conditions, and 600 mg zileuton immediate-release tablets every 6 hours under fed conditions until steady state zileuton levels were achieved. Food increased AUC and Cmin of Zyflo CR by 43% and 170%, respectively, but had no effect on Cmax. Therefore, Zyflo CR is recommended to be administered with food [see Dosage and Administration (2)]. At steady state, relative bioavailability of Zyflo CR to zileuton immediate-release tablets with respect to Cmax, Cmin, and AUC were 0.65 (90% CI: 0.60, 0.71), 1.05 (90% CI: 0.88, 1.25) and 0.85 (90% CI: 0.78, 0.92) respectively. These data indicate that at steady state under fed conditions the Cmax of Zyflo CR is about 35% lower than that of zileuton immediate-release tablets but the Cmin and AUC are similar for both formulations.

Distribution

The apparent volume of distribution (V/F) of zileuton is approximately 1.2 L/kg. Zileuton is 93% bound to plasma proteins, primarily to albumin, with minor binding to α1‑acid glycoprotein.

Elimination

Elimination of zileuton is predominantly via metabolism with a mean terminal half-life of 3.2 hours. Apparent oral clearance (CL/F) of zileuton is 669 mL/min. Zileuton activity is primarily due to the parent drug. Studies with radiolabeled drug have demonstrated that orally administered zileuton is well absorbed into the systemic circulation with 94.5% and 2.2% of the radiolabeled dose recovered in urine and feces, respectively.

Metabolism

In vitro studies utilizing human liver microsomes have shown that zileuton and its N-dehydroxylated metabolite can be oxidatively metabolized by CYP1A2, CYP2C9 and CYP3A4.

Several zileuton metabolites have been identified in human plasma and urine. These include two diastereomeric O-glucuronide conjugates (major metabolites) and an N-dehydroxylated metabolite (A-66193) of zileuton. The urinary excretion of the inactive A-66193 metabolite and unchanged zileuton each accounted for less than 0.5% of the single radiolabeled dose. Multiple doses of 1200 mg Zyflo CR twice daily resulted in peak plasma levels of 4.9 µg/mL of the inactive metabolite A-66193 with an AUC of 93 µg∙hr/mL, showing large inter-subject variability. This inactive metabolite has been shown to be formed by the gastrointestinal microflora prior to the absorption of zileuton and its formation increases with delayed absorption of zileuton.

Renal Impairment

The pharmacokinetics of zileuton immediate-release tablets were similar in healthy subjects and in subjects with mild, moderate, and severe renal insufficiency. In subjects with renal failure requiring hemodialysis, zileuton pharmacokinetics were not altered by hemodialysis and a very small percentage of the administered zileuton dose (<0.5%) was removed by hemodialysis. Hence, dosing adjustment in patients with renal dysfunction or undergoing hemodialysis is not necessary.

Hepatic Impairment

The pharmacokinetics of zileuton immediate-release tablets were compared between subjects with mild and moderate chronic hepatic insufficiency. The mean apparent plasma clearance of total zileuton in subjects with hepatic impairment was approximately half the value of the healthy subjects. The percent binding of zileuton to plasma proteins after multiple dosing was significantly reduced in patients with moderate hepatic impairment. Zyflo CR is contraindicated in patients with active liver disease or persistent ALT elevations ≥3×ULN [see Warnings and Precautions (5)].

Geriatric Use

The pharmacokinetics of zileuton immediate-release tablets were investigated in healthy elderly subjects (ages 65 to 81 years, 9 males, 9 females) and healthy young subjects (ages 20 to 40 years, 5 males, 4 females) after single and multiple oral doses of 600 mg zileuton every 6 hours. Zileuton pharmacokinetics were similar in healthy elderly subjects (≥65 years) compared to healthy younger adults (20 to 40 years).

More frequent side effects include: dyspepsia. See below for a comprehensive list of adverse effects.