Before you begin taking a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take this medication.
Asthma attacks: Zafirlukast should not be used to try to relieve acute asthma attacks. Have your rescue medication ready in case of an acute attack. Do not stop taking zafirlukast without consulting your doctor.
Liver problems: Zafirlukast is not recommended for people with reduced liver function. It may also cause severe liver problems. If you develop jaundice (signs include yellowing of the skin or eyes); flu-like symptoms; nausea; fatigue; loss of appetite; itching; and pain on the right side of your abdomen, under the ribcage, stop taking this medication and contact your doctor immediately.
Warfarin interaction: Taking warfarin together with zafirlukast significantly increases the time it takes blood to clot. People taking warfarin and zafirlukast should have their bleeding times monitored closely and have their anticoagulant dose (warfarin) adjusted accordingly.
Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.
Breast-feeding: Zafirlukast passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.
Children: The effectiveness and safety of zafirlukast for children under 12 years of age have not been established.