Relationships between plasma theophylline clearance, liver volume and body weight in children and adults.

The influence of liver volume and body weight on plasma theophylline clearance was investigated in asthmatic children and adults. A linear relationship (r = +0.99) was demonstrated between ideal body weight and liver volume estimated by an ultrasonic scanning technique. Age-related changes in liver volume-to-body weight ratio could account for only 30% of differences in plasma theophylline clearance (1/h/kg) between children and adults. It is summized that increased hepatic mixed function oxidase activity is the major contributor to the higher plasma theophylline clearance in children.