In Reply.—Drs Wilschanski and Kaplan offer an interesting observation on their patient that, in fact, concurs with the initial hypothesis we held when we began analyzing our data, ie, that the phenobarbital may have been increasing the theophylline clearance and dropping the serum levels to subtherapeutic values.
Unfortunately, when we began analysis of our group 3 infants (those with both apnea and seizures while receiving both drugs), in only a few of the patients was the interval between the onset of apnea and the onset of seizures long enough to allow the serum level of theophylline to be measured before the initiation of phenobarbital administration. Our routine protocol calls for the theophylline level first to be measured 24 to 48 hours after the start of maintenance therapy. Thus, we were unable to examine statistically the very important point that Drs Wilschanski and Kaplan raise. However, the statistics comparing our