5.1 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.

5.2 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)].

6.1 Short-Term Clinical Studies Experience

The safety data described below reflect exposure to ZYFLO CR in 199 patients for 12 weeks duration.  In a 12-week, randomized, double-blind, placebo-controlled trial in adults and adolescents 12 years of age and older with asthma, patients received ZYFLO CR two 600 mg tablets (n=199) or placebo (n=198) twice daily by mouth.  Eighty-three percent of patients were white, 48% were male, and the mean age was 34 years.

Because clinical studies are conducted under widely varying conditions, adverse reaction rates observed in the clinical studies of a drug cannot be directly compared to rates in the clinical studies of another drug and may not reflect the rates observed in practice.

The most commonly reported adverse reactions (occurring at a frequency of ≥5%) in ZYFLO CR-treated patients and at a frequency greater than placebo-treated patients are reflected in Table 1.

Table 1.

Adverse Reactions with ≥5% Incidence in a 12‑Week Placebo-Controlled Trial in Patients with Asthma.

Less common adverse reactions occurring at a frequency ≥1% and more often in the ZYFLO CR group than in the placebo group included gastrointestinal disorders (upper abdominal pain, diarrhea, dyspepsia, vomiting), rash, hypersensitivity, and hepatotoxicity.

There were no differences in the incidence of adverse reactions based upon gender.  The clinical trials did not include sufficient numbers of patients <18 years of age or non-Caucasians to determine whether there is any difference in adverse reactions based upon age or race.

6.2 Long-Term Clinical Studies Experience

The safety of ZYFLO CR was evaluated in one 6-month, randomized, double-blind, placebo-controlled clinical trial in adults and adolescents 12 years of age and older with asthma. Patients received two 600 mg ZYFLO CR tablets (n=619) or placebo (n=307) twice daily by mouth along with usual asthma care. Eighty-six percent of patients were white, 40% were male, and the overall mean age was 36.

The rate and type of adverse reactions observed in this study were comparable to the adverse reactions observed in the 12-week study. Other commonly reported adverse reactions (occurring at a frequency of ≥5%) in ZYFLO CR-treated patients and at a frequency greater than placebo-treated patients included the following: headache (23%), upper respiratory tract infection (9%), myalgia (7%), and diarrhea (5%) compared to 21%, 7%, 5% and 2%, respectively, in the placebo-treated group.

ALT elevations (≥3×ULN) were observed in 1.8% of patients treated with ZYFLO CR compared to 0.7% in patients treated with placebo. The majority of elevations (82%) were reported within the first 3 months of treatment and resolved within 21 days for most of these patients after discontinuation of the drug. The hepatic function enzyme elevations attributed to ZYFLO CR did not result in any cases of jaundice, development of chronic liver disease, or death in this clinical trial.

Occurrences of low white blood cell (WBC) count (<3.0 × 109/L) were observed in 2.6% (15 of 619) of the ZYFLO CR-treated patients and in 1.7% (5 of 307) of the placebo-treated patients. The WBC counts returned to normal or baseline following discontinuation of ZYFLO CR. The clinical significance of these findings is not known.

6.3 Postmarketing Experience

The following adverse reactions have been identified during post-approval use of zileuton immediate-release tablets and may be applicable to ZYFLO CR. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship.

Cases of severe hepatic injury have been reported in patients taking zileuton immediate-release tablets. These cases included death, life-threatening liver injury with recovery, symptomatic jaundice, hyperbilirubinemia, and elevations of ALT >8×ULN.

Cases of sleep disorders and behavior changes have also been reported [see Warnings and Precautions (5.2)].

7.1 Theophylline

In a drug-interaction study in 16 healthy subjects, co-administration of multiple doses of zileuton immediate-release tablets (800 mg every 12 hours) and theophylline (200 mg every 6 hours) for 5 days resulted in a significant decrease (approximately 50%) in steady-state clearance of theophylline, an approximate doubling of theophylline AUC, and an increase in theophylline Cmax (by 73%). The elimination half-life of theophylline was increased by 24%. Also, during co-administration, theophylline-related adverse reactions were observed more frequently than after theophylline alone. Upon initiation of ZYFLO CR in patients receiving theophylline, the theophylline dosage should be reduced by approximately one-half and plasma theophylline concentrations monitored. Similarly, when initiating therapy with theophylline in a patient receiving ZYFLO CR, the maintenance dose and/or dosing interval of theophylline should be adjusted accordingly and guided by serum theophylline determinations.

7.2 Warfarin

Concomitant administration of multiple doses of zileuton immediate-release tablets (600 mg every 6 hours) and warfarin (fixed daily dose obtained by titration in each subject) to 30 healthy male subjects resulted in a 15% decrease in R-warfarin clearance and an increase in AUC of 22%. The pharmacokinetics of S-warfarin were not affected. These pharmacokinetic changes were accompanied by a clinically significant increase in prothrombin times. Monitoring of prothrombin time, or other suitable coagulation tests, with the appropriate dose titration of warfarin is recommended in patients receiving concomitant ZYFLO CR and warfarin therapy.

7.3 Propranolol

Co-administration of zileuton immediate-release tablets and propranolol results in a significant increase in propranolol concentrations. Administration of a single 80 mg dose of propranolol in 16 healthy male subjects who received zileuton immediate-release tablets 600 mg every 6 hours for 5 days resulted in a 42% decrease in propranolol clearance. This resulted in an increase in propranolol Cmax, AUC, and elimination half-life by 52%, 104%, and 25%, respectively. There was an increase in β-blockade as shown by a decrease in heart rate associated with the co-administration of these drugs. Patients concomitantly on ZYFLO CR and propranolol should be closely monitored and the dose of propranolol reduced as necessary. No formal drug-drug interaction studies between zileuton and other beta-adrenergic blocking agents (i.e., β-blockers) have been conducted. It is reasonable to employ appropriate clinical monitoring when these drugs are co-administered with ZYFLO CR.

7.4 Other Concomitant Drug Therapy

Drug-drug interaction studies conducted in healthy subjects between zileuton immediate-release tablets and prednisone and ethinyl estradiol (oral contraceptive), drugs known to be metabolized by the CYP3A4 isoenzyme, have shown no significant interaction. However, no formal drug-drug interaction studies between zileuton and CYP3A4 inhibitors, such as ketaconazole, have been conducted. It is reasonable to employ appropriate clinical monitoring when these drugs are co-administered with ZYFLO CR.

Drug-drug interaction studies in healthy subjects have been conducted with zileuton immediate-release tablets and digoxin, phenytoin, sulfasalazine, and naproxen. There was no significant interaction between zileuton and any of these drugs.

8.1 Pregnancy

Risk Summary

There are no adequate human data on ZYFLO CR use in pregnant women to inform a drug associated risk. In animal studies, oral administration of zileuton to pregnant rats and rabbits during organogenesis produced adverse developmental outcomes. Structural abnormalities (cleft palate) were observed in rabbits at a dose similar to the maximum recommended human daily oral dose (MRHD), and alterations to growth (reduced fetal body weight and increased skeletal variations) were observed in rats at maternal plasma exposures 20 times greater than at the MRHD [see Data]. In a pre- and post-natal development study, oral administration of zileuton to pregnant rats from organogenesis through weaning at maternal plasma exposures 20 times greater than the MRHD resulted in reduced pup survival and body weights. Zileuton and/or its metabolites cross the placental barrier of rats; therefore, ZYFLO CR may be transmitted from the mother to the developing fetus.

In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2-4% and 15-20%, respectively.

Pregnancy Exposure Registry

There is a pregnancy exposure registry that monitors pregnancy outcomes in women exposed to asthma medications during pregnancy. For more information, contact the MothersToBaby Pregnancy Studies conducted by the Organization of Teratology Information Specialists at 1-877-311-8972 or visit http://mothertobaby.org/pregnancy-studies/.

Data

Animal Data

In a fertility and general reproductive performance study in rats, 0, 15, 75, 150 or 300 mg/kg/day zileuton was administered orally to male and female rats. The treated males were dosed daily for 100 days prior to mating with the treated females and 80 days prior to mating with untreated females, and throughout the mating periods. The treated females were dosed for 14 days before mating with untreated males and dosing continued throughout gestation, and in 1/3 of the females through parturition and lactation period. Maternal body weight gain was reduced at 150 and 300 mg/kg/day groups (9-12% differences in body weight relative to controls).

During fetal evaluation, zileuton produced lower litter size (7.1 pup/dams at 300 mg/kg/day vs. 9.6 pup/dams at 150 mg/kg/day vs. 13.5 pup/dams in control group), lower fetal weights (-9%), decreased viable fetuses, and increased in unossification of fetal skeletal structure at 300 mg/kg at exposures greater than 20 times the MRHD (on an AUC basis with data obtained from the comparable doses of 3-month general toxicity study). There were no embryofetal effects at 150 mg/kg/day.

During post-natal development evaluation, zileuton produced decrease in pup viability (-16% at 150 mg/kg/day and -43.5% at 300 mg/kg/day on lactation Day 4) as well as depression of body weight gain in pups at ≥ 150 mg/kg/day at exposures close to 20 times the MRHD (on an AUC basis with data obtained from the comparable doses of 1-year general toxicity study). Observations of lower pup weight and survival rate at 300 mg/kg/day group were confirmed in a peri- & post-natal study administered with the same dose levels in pregnant rats.

In a teratology study in pregnant rabbits, 0, 15, 50 or 150 mg/kg/day zileuton was administered orally to pregnant animals during organogenesis. Cleft palate was noted in three of 118 (2.5%) rabbit fetuses (or 2 of 17 litters) at 150 mg/kg/day. Additionally, two fetuses (1.7%) had domed head and two fetuses (1.7%) had hydrocephalus also at 150 mg/kg/day which was equivalent to the MRHD on a mg/m2 basis. There were no adverse developmental outcomes at 50 mg/kg/day (approximately one-third the MRHD on a mg/m2 basis).

Oral dose of 5 mg radiolabeled zileuton indicated that zileuton crosses the placental barrier of rats.

8.2 Lactation

Risk Summary

Zileuton and/or its metabolites are excreted in rat milk. It is not known if zileuton is excreted in human milk, nor are there data on the effects of the drug on the breastfed infant or effects on maternal milk production. Because many drugs are excreted in human milk, and because of the potential for tumorigenicity of zileuton shown in animal studies, the developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for Zyflo CR and any potential adverse effects on the breastfed child from Zyflo CR or from the underlying maternal condition. 

Data

Animal Data

Following an oral 70 mg/kg dose of radiolabeled 14C-zileuton to lactating rats, total radioactivity was distributed into the milk of dams, but the mean concentrations did not exceed those in plasma.

8.4 Pediatric Use

The safety and effectiveness of ZYFLO CR in pediatric patients under 12 years of age have not been established. FDA has not required pediatric studies in patients under the age of 12 years due to the risk of hepatotoxicity. ZYFLO CR is not appropriate for children less than 12 years of age.

8.5 Geriatric Use

Subgroup analysis of controlled and open-label clinical studies with zileuton immediate-release tablets suggests that females ≥65 years of age appear to be at increased risk of ALT elevations. In ZYFLO CR placebo-controlled studies there were no discernable trends in ALT elevations noted in subset analyses for patients ≥65 years of age, although the database may not have been sufficiently large to detect a trend [see Pharmacokinetics (12.3)].

8.6 Renal Impairment

Dosing adjustment in patients with renal dysfunction or patients undergoing hemodialysis is not necessary [see Pharmacokinetics (12.3)].

8.7 Hepatic Impairment

ZYFLO CR is contraindicated in patients with active liver disease or persistent ALT elevations ≥3×ULN [see Warnings and Precautions (5) and Pharmacokinetics (12.3)].

12.1 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.

12.2 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.

12.3 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.

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

In 2-year carcinogenicity studies, increases in the incidence of liver, kidney, and vascular tumors in female mice and a trend toward an increase in the incidence of liver tumors in male mice were observed at 450 mg/kg/day (providing approximately 5 times [females] or 8 times [males] the systemic exposure [AUC=64 μg·hr/mL] achieved at the MRHD).  No increase in the incidence of tumors was observed at 150 mg/kg/day (providing approximately 2-3 times the systemic exposure [AUC] achieved at the MRHD).  In rats, an increase in the incidence of kidney tumors was observed in both sexes at 170 mg/kg/day (providing approximately 8 times [males] or 16 times [females] the systemic exposure [AUC] achieved at the MRHD).  No increased incidence of kidney tumors was seen at 80 mg/kg/day (providing approximately 4 times [males] or 7 times [females] the systemic exposure [AUC] achieved at the MRHD).  Although a dose-related increased incidence of benign Leydig cell tumors was observed, Leydig cell tumorigenesis was prevented by supplementing male rats with testosterone.

Zileuton was negative in genotoxicity studies including bacterial reverse mutation (Ames) using S. typhimurium and E. coli, chromosome aberration in human lymphocytes, in vitro unscheduled DNA synthesis (UDS), in rat hepatocytes with or without zileuton pretreatment and in mouse and rat kidney cells with zileuton pretreatment, and mouse micronucleus assays.  However, a dose-related increase in DNA adduct formation was reported in kidneys and livers of female mice treated with zileuton.  Although some evidence of DNA damage was observed in a UDS assay in hepatocytes isolated from Aroclor-1254-treated rats, no such finding was noticed in hepatocytes isolated from monkeys, where the metabolic profile of zileuton is more similar to that of humans.

In reproductive performance/fertility studies, zileuton produced no effects on fertility in rats at oral doses up to 300 mg/kg/day (providing at least 10 times [male rats] and greater than 20 times [female rats] the systemic exposure [AUC] achieved at the MRHD).  However, reduction in fetal implants was observed at oral doses of 150 mg/kg/day and higher (providing approximately 20 times the systemic exposure [AUC] achieved at the MRHD).  Comparative systemic exposure (AUC) is based on measurements in male rats or nonpregnant female rats obtained from the comparable doses of 3-month or 1-year general toxicity study at similar dosages.  Increases in gestation length, prolongation of estrus cycle, and increases in stillbirths were observed at oral doses of 75 mg/kg/day and higher (providing approximately 7 times the systemic exposure [AUC] achieved at the MRHD on an AUC basis with data obtained from the comparable doses of 2-year dietary carcinogenicity study).  No adverse effects were observed at 15 mg/kg/day in the study at estimated exposure similar to that at the MRHD.

Store between 20 and 25°C (68-77ºF); excursions permitted to 15-30°C (59-86°F) [see USP Controlled Room Temperature]. Protect from light.

17.1 Information for Patients

Patients should be told that:

• ZYFLO CR is indicated for the chronic treatment of asthma and should be taken regularly as prescribed, even during symptom-free periods.
• ZYFLO CR is a leukotriene synthesis inhibitor which works by inhibiting the formation of leukotrienes.
• ZYFLO CR should be taken within one hour after morning and evening meals.
• ZYFLO CR tablets should not be cut, chewed or crushed.
• ZYFLO CR is not a bronchodilator and should not be used to treat acute episodes of asthma.
• When taking ZYFLO CR, they should not decrease the dose or stop taking any other antiasthma medications unless instructed by a health care provider. If a dose is missed, they should take the next dose at the scheduled time and not double the dose.
• While using ZYFLO CR, medical attention should be sought if short-acting bronchodilators are needed more often than usual, or if more than the maximum number of inhalations of short-acting bronchodilator treatment prescribed for a 24-hour period are needed.
• The most serious side effect of ZYFLO CR is potential elevation of liver enzymes (in 2% of patients) and that, while taking ZYFLO CR, they must return for liver enzyme test monitoring on a regular basis.
• If they experience signs and/or symptoms of liver dysfunction (e.g., right upper quadrant pain, nausea, fatigue, lethargy, pruritus, jaundice, or "flu-like" symptoms), they should contact their health care provider immediately.
• Patients should be instructed to notify their healthcare provider if neuropsychiatric events occur while using ZYFLO CR.
• ZYFLO CR can interact with other drugs and that, while taking ZYFLO CR, they should consult their health care provider before starting or stopping any prescription or non-prescription medicines.
• A patient leaflet is included with the tablets.

CTZC-001-0119-03-SPL

Manufactured for:

Chiesi USA, Inc.

Cary, NC 27518