Development of N-demethylase activity measured with the 13C-aminopyrine breath test

The 13C-aminopyrine (AP) breath test was used to measure the normal development of N-demethylase activity in 25 children, aged 2 days to 14 years, with normal liver function. Five mg of 13C-AP per kg body weight were administered orally. After AP-demethylation by the hepatic mixed function oxidase system 13CO2 excess was analysed in expired breath by mass spectrometry. In the first days of life no 13C excretion could be detected in unstimulated newborns. N-demethylase activity then slowly increased and reached adult levels by two years of life. Though the range of normal values showed considerable scattering, patients with liver disease or with enzyme induction following anticonvulsant therapy could be well discriminated. This study of the 13C-aminopyrine breath test in children provides evidence for the assumption that hepatocellular function and development of specific enzymatic activities can be measured by such non-invasive methods. It may be expected that breath tests making use of a broader spectrum of 13C-labeled substrates will prove applicable to study prenatal inducibility and other aspects of developing hepatocellular and intestinal function of children in health and disease.