Rifampicin increases the clearance of
theophylline by 45%. In one study
rifampicin (with isoniazid) increased
theophylline clearance during the initial few days of
tuberculosis treatment, but another study suggested that these antituberculars
decreased
theophylline clearance within 4 weeks.
Monitor
theophylline levels. An effect has been seen within 36 hours of starting
rifampicin. Expect to need to increase the
theophylline dose. The picture is less
clear when isoniazid is also taken. In this situation it would seem prudent to
monitor
theophylline levels closely for the first month of treatment.