RESUMO
Background: 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. Methods: 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. Results: 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). Conclusion: 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.
RESUMO
BACKGROUND: The salivary caffeine clearance is a non-invasive, safe, saliva-based method for assessing hepatic function and diagnosing chronic liver disease. The elimination of caffeine from the body follows first-order kinetics and principally involves catabolism by hepatic CYP1A2, with a half-life usually between three and 7 h. It is known that this process is affected by age and smoking tobacco. It has been suggested that sex might also be important, but there is scant evidence for this. The aim of this study was to assess whether there is a sex difference in salivary caffeine clearance in adults. METHODS: A cohort of 213 adults was studied. They were all non-smokers and none suffered from chronic liver disease. They consisted of 67 men (mean age 40.0 years) and 146 women (mean age 44.7 years). Following a period of dietary caffeine abstinence lasting at least 24 h, each subject ingested a single oral dose in the morning of caffeine, at a dose of 3 mg per kg body mass. Salivary samples were collected at 2 h and 14 h post-caffeine ingestion and were spectrophotometrically assayed for their caffeine concentrations. RESULTS: The two groups were matched for age. The mean (standard error) salivary caffeine clearance in the male subjects was 1.51 (0.10) mL min-1 kg-1, while that in the female subjects was 1.60 (0.07) mL min-1 kg-1 (p = 0.495). CONCLUSION: This relatively large study provides no evidence of a sex difference in salivary caffeine clearance.
