The [14C]-aminopyrine breath test. A comparison of different forms of analysis

1 Following ingestion of [14C]-aminopyrine, breath 14CO2 data were analysed from normal individuals, patients with hepatic disease, epileptics receiving anticonvulsant therapy and volunteers before and after treatment with glutethimide. 2 The 'standard' 2 h [14C]-aminopyrine breath test discriminated successfully between the main groups but failed to detect the change in microsomal enzyme function produced by glutethimide. 3 A 'modified' form of the 2 h breath test calculated from the area under the breath specific activity curve detected the increase in demethylation following glutethimide. 4 The breath elimination constant (Kb) derived from the breath 14CO2 disappearance curve was as sensitive as the 'modified' 2 h breath test and was simpler to compute. 5 Glutethimide 500 mg/day for 14 days resulted in a 42% increase in the metabolic clearance of antipyrine and a 26% increase in demethylation of [14C]-aminopyrine.