Assessment of dimethylxanthine formation from caffeine in healthy adults: comparison between plasma and saliva concentrations and urinary excretion of metabolites.
Caffeine (CA), paraxanthine (PX), theobromine (TB) and theophylline (TP) were determined in plasma (i.e. total concentrations), ultrafiltrate of plasma (free concentrations) and saliva, by isocratic high performance liquid chromatography (HPLC), 0-24 h after a 200 mg oral load of CA in 10 healthy adults. Total metabolism of CA was established by determination of urinary metabolites, 24 h after CA ingestion, by gradient HPLC and capillary electrophoresis. Saliva concentrations of CA, PX, and TP were lower than plasma concentrations (p