Terfenadine reduced the
mean maximum
serum levels of
zafirlukast by about 70% and reduced its AUC by about 60% in one study. Terfenadine
serum levels remained unchanged and no ECG alterations occurred.
The reduction in
zafirlukast serum levels would be expected to reduce its antiasthmatic effects, but this needs
clinical assessment. The combination need not be avoided but be alert for a reduced response.