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Zyflo CR (Zileuton) - Warnings and Precautions




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.


Information on specific populations is based on studies conducted with zileuton immediate-release tablets and is applicable to ZYFLO CR.


Pregnancy Category C:

Developmental studies indicated adverse effects (reduced body weight and increased skeletal variations) in rats at an oral dose of 300 mg/kg/day (providing greater than 10 times the systemic exposure [AUC] achieved at the maximum recommended human daily oral dose). Comparative systemic exposure [AUC] is based on measurements in nonpregnant female rats at a similar dosage. Zileuton and/or its metabolites cross the placental barrier of rats. Three of 118 (2.5%) rabbit fetuses had cleft palates at an oral dose of 150 mg/kg/day (equivalent to the maximum recommended human daily oral dose on a mg/m2 basis). There are no adequate and well-controlled studies in pregnant women. ZYFLO CR should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

Zileuton and/or its metabolites are excreted in rat milk. It is not known if zileuton is excreted in human milk. Because many drugs are excreted in human milk, and because of the potential for tumorigenicity shown for zileuton in animal studies, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

Pediatric Use

The safety and effectiveness of ZYFLO CR in pediatric patients under 12 years of age have not been established. ZYFLO CR is not appropriate for children less than 12 years of age.

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 ].

Renal Impairment

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

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 ].

Page last updated: 2007-08-03

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