Effect of secobarbital on theophylline clearance.

Increased clearance of theophylline after the administration of secobarbital was observed in a child receiving phenobarbital. Prior to barbiturate treatment, theophylline clearance was 4.78 ml/kg/min. Beginning 10 days after the institution of secobarbital and phenobarbital therapy, a continually increasing amount of theophylline was required to maintain therapeutic serum concentrations. After 29 days of barbiturate administration, theophylline clearance attained a peak value of 16.1 ml/kg/min, an increase of 337% from the prebarbiturate rate. During this time it was necessary to administer theophylline at a dosage four times above that usually recommended. After secobarbital was discontinued, theophylline clearance returned to 4.53 ml/kg/min. The decrease in theophylline clearance occurred while phenobarbital dosage remained stable. It is apparent that changes in secobarbital dosing were subsequently followed by changes in the clearance of theophylline.