Terfenadine reduced the mean
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.