Salivary clearance of caffeine in children

Measurement of salivary caffeine (1,3,7-trimethylpurine-2,6-dione or 1,3,7-trimethylxanthine) clearance can, in principle, be used to assess hepatic function, diagnose chronic hepatic disease and conduct investigations of substrates of hepatic cytochrome P450 (CYP) isozymes in children, without recourse to venepuncture. However, little is known about childhood sexual dimorphism of hepatic CYP isoforms. Furthermore, the association, if any, between salivary caffeine clearance and age in children has not hitherto been established. The aims of this study were to assess whether salivary caffeine clearance differs between boys and girls and whether it varies with age during childhood.

Following at least 24 h' abstinence from dietary caffeine, nine boys (mean (standard error) age 9.6 (1.1) y) and eight girls (mean age 11.0 (1.2) y), none of whom was a smoker or suffered from chronic hepatic disease, ingested an oral caffeine dose titrated by body mass, namely 3 mg kg^-1. Salivary samples collected two and 14 h later underwent spectrophotometric caffeine analysis.

The boys and the girls were age matched. The mean caffeine clearance in the boys was 2.47 (0.33) mL min^-1 kg^-1, while that in the girls was 2.20 (0.31) mL min^-1 kg^-1 (p = 0.56). The salivary caffeine clearance was negatively correlated with age (r = -0.59, p = 0.01).

Stratification by sex appears to be unnecessary when considering childhood salivary caffeine clearance or when conducting investigations in children of CYP1A2 and xanthine oxidase substrates. Furthermore, childhood salivary caffeine clearance is negatively correlated with age.