PHENOBARBITAL AND THEOPHYLLINE

Theophylline serum levels can be reduced by phenobarbital or pentobarbital (clearance increased by roughly one-third). A single report describes a similar interaction with secobarbital, and an interaction would be expected to occur with other barbiturates. Limited evidence suggests that the barbiturates may have a greater effect in children, and if given in high dose.
It would be prudent to monitor theophylline levels if a barbiturate is added to or withdrawn from theophylline treatment.