Zafirlukast is indicated for the prophylaxis and chronic treatment of asthma in adults and children 5 years of age and older.
Zafirlukast is contraindicated in patients who are hypersensitive to zafirlukast or any of its inactive ingredients.
Zafirlukast is contraindicated in patients with hepatic impairment including hepatic cirrhosis.
Cases of life-threatening hepatic failure have been reported in patients treated with zafirlukast. Cases of liver injury without other attributable cause have been reported from post-marketing adverse event surveillance of patients who have received the recommended dose of zafirlukast (40 mg/day). In most, but not all post-marketing reports, the patient’s symptoms abated and the liver enzymes returned to normal or near normal after stopping zafirlukast. In rare cases, patients have either presented with fulminant hepatitis or progressed to hepatic failure, liver transplantation and death. In extremely rare post-marketing cases, no clinical symptoms or signs suggestive of liver dysfunction were reported to precede the latter observations.
Physicians may consider the value of liver function testing. Periodic serum transaminase testing has not proven to prevent serious injury but it is generally believed that early detection of drug-induced hepatic injury along with immediate withdrawal of the suspect drug enhances the likelihood for recovery.
Patients should be advised to be alert for signs and symptoms of liver dysfunction (eg, right upper quadrant abdominal pain, nausea, fatigue, lethargy, pruritus, jaundice, flu-like symptoms, and anorexia) and to contact their physician immediately if they occur. Ongoing clinical assessment of patients should govern physician interventions, including diagnostic evaluations and treatment.
If liver dysfunction is suspected based upon clinical signs or symptoms (eg, right upper quadrant abdominal pain, nausea, fatigue, lethargy, pruritus, jaundice, flu-like symptoms, anorexia, and enlarged liver), zafirlukast should be discontinued.
Liver function tests, in particular serum ALT, should be measured immediately and the patient managed accordingly. If liver function tests are consistent with hepatic dysfunction, zafirlukast therapy should not be resumed. Patients in whom zafirlukast was withdrawn because of hepatic dysfunction where no other attributable cause is identified should not be re-exposed to zafirlukast (see PRECAUTIONS, Information for Patients and ADVERSE REACTIONS).
Zafirlukast is not indicated for use in the reversal of bronchospasm in acute asthma attacks, including status asthmaticus. Therapy with zafirlukast can be continued during acute exacerbations of asthma.
Concomitant Warfarin Administration:
Coadministration of zafirlukast with warfarin results in a clinically significant increase in prothrombin time (PT). Patients on oral warfarin anticoagulant therapy and zafirlukast should have their prothrombin times monitored closely and anticoagulant dose adjusted accordingly (see PRECAUTIONS, Drug Interactions).
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Patients should be told that a rare side effect of zafirlukast is hepatic dysfunction, and to contact their physician immediately if they experience symptoms of hepatic dysfunction (eg. right upper quadrant abdominal pain, nausea, fatigue, lethargy, pruritus, jaundice, flu-like symptoms, and anorexia). Liver failure resulting in liver transplantation and death has occurred in patients taking zafirlukast (see WARNINGS, Hepatotoxicity and ADVERSE REACTIONS).
Zafirlukast is indicated for the chronic treatment of asthma and should be taken regularly as prescribed, even during symptom-free periods. Zafirlukast is not a bronchodilator and should not be used to treat acute episodes of asthma. Patients receiving zafirlukast should be instructed not to decrease the dose or stop taking any other antiasthma medications unless instructed by a physician. Patients should be instructed to notify their physician if neuropsychiatric events occur while using zafirlukast (see PRECAUTIONS, Neuropsychiatric Events). Women who are breast-feeding should be instructed not to take zafirlukast (see PRECAUTIONS, Nursing Mothers). Alternative antiasthma medication should be considered in such patients.
The bioavailability of zafirlukast may be decreased when taken with food. Patients should be instructed to take zafirlukast at least 1 hour before or 2 hours after meals.
In rare cases, patients with asthma on zafirlukast may present with systemic eosinophilia, eosinophilic pneumonia, or clinical features of vasculitis consistent with Churg-Strauss syndrome, a condition which is often treated with systemic steroid therapy. Physicians should be alert to eosinophilia, vasculitic rash, worsening pulmonary symptoms, cardiac complications, and/or neuropathy presenting in their patients. These events have usually, but not always, been associated with reductions and/or withdrawal of steroid therapy. The possibility that zafirlukast may be associated with emergence of Churg-Strauss syndrome can neither be excluded nor established (see ADVERSE REACTIONS).
Neuropsychiatric events have been reported in adult, adolescent and pediatric patients taking zafirlukast. Post-marketing reports with zafirlukast include insomnia and depression. The clinical details of some post-marketing reports involving zafirlukast 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 zafirlukast if such events occur (see ADVERSE REACTIONS).
In a drug interaction study in 16 healthy male volunteers, coadministration of multiple doses of zafirlukast (160 mg/day) to steady-state with a single 25 mg dose of warfarin resulted in a significant increase in the mean AUC (+ 63%) and half-life (+36%) of S-warfarin. The mean prothrombin time (PT) increased by approximately 35%. This interaction is probably due to an inhibition by zafirlukast of the cytochrome P450 2C9 isoenzyme system. Patients on oral warfarin anticoagulant therapy and zafirlukast should have their prothrombin times monitored closely and anticoagulant dose adjusted accordingly (see WARNINGS, Concomitant Warfarin Administration). No formal drug-drug interaction studies with zafirlukast and other drugs known to be metabolized by the cytochrome P450 2C9 isoenzyme (eg, tolbutamide, phenytoin, carbamazepine) have been conducted; however, care should be exercised when zafirlukast is coadministered with these drugs.
In a drug interaction study in 11 asthmatic patients, coadministration of a single dose of zafirlukast (40 mg) with erythromycin (500 mg three times daily for 5 days) to steady-state resulted in decreased mean plasma levels of zafirlukast by approximately 40% due to a decrease in zafirlukast bioavailability.
Coadministration of zafirlukast (20 mg/day) or placebo at steady-state with a single dose of sustained release theophylline preparation (16 mg/kg) in 16 healthy boys and girls (6 through 11 years of age) resulted in no significant differences in the pharmacokinetic parameters of theophylline.
Coadministration of zafirlukast (80 mg/day) at steady-state with a single dose of a liquid theophylline preparation (6 mg/kg) in 13 asthmatic patients, 18 to 44 years of age, resulted in decreased mean plasma levels of zafirlukast by approximately 30%, but no effect on plasma theophylline levels was observed.
Rare cases of patients experiencing increased theophylline levels with or without clinical signs or symptoms of theophylline toxicity after the addition of zafirlukast to an existing theophylline regimen have been reported. The mechanism of the interaction between zafirlukast and theophylline in these patients is unknown (see ADVERSE REACTIONS).
Coadministration of zafirlukast (40 mg/day) with aspirin (650 mg four times daily) resulted in mean increased plasma levels of zafirlukast by approximately 45%.
In a single-blind, parallel-group, 3-week study in 39 healthy female subjects taking oral contraceptives, 40 mg twice daily of zafirlukast had no significant effect on ethinyl estradiol plasma concentrations or contraceptive efficacy.
Coadministration of zafirlukast with fluconazole, a moderate CYP2C9 inhibitor, resulted in increased plasma levels of zafirlukast, by approximately 58% (90% CI:28, 95). The clinical significance of this interaction is unknown. Zafirlukast exposure is likely to be increased by other moderate and strong CYP2C9 inhibitors. Coadministration of zafirlukast with itraconazole, a strong CYP3A4 inhibitor, caused no change in plasma levels of zafirlukast.
No other formal drug-drug interaction studies between zafirlukast and marketed drugs known to be metabolized by the P450 3A4 (CYP3A4) isoenzyme (eg, dihydropyridine calcium-channel blockers, cyclosporin, cisapride) have been conducted. As zafirlukast is known to be an inhibitor of CYP3A4 in vitro , it is reasonable to employ appropriate clinical monitoring when these drugs are coadministered with zafirlukast.
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