4. Zafirlukast is pregnancy category B. There are no adequate and well-controlled trials in pregnant women. Therefore, the effects of zafirlukast on the developing human fetus are unknown. For this reason, women of child-bearing potential must agree to use adequate contraception: hormonal or barrier method of birth control, prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she is participating in this study, she should inform her treating physician immediately.