Prandial and diurnal effects on the absorption of orally administered enteric coated 5-aminosalicylic acid (5-ASA).

Plasma and urine concentrations of 5-ASA and its N-acetyl metabolite 5-AcASA were measured over 48 h in 12 young healthy male subjects, who received three doses of three times enteric coated 500 mg 5-ASA tablets at 7 h interval, on two occasions 14 days apart. On one occasion the doses were given after standard meals; on the other occasion, they were given 1 h before meals. Administration of the tablets after meals delayed systemic drug absorption but did not affect the extent of absorption. There was a sharp rise in the plasma concentrations of 5-ASA and 5-AcASA in the early morning (i.e. circa 24 h after administration of the 1st dose) independent of when the tablets were taken with respect to the meals. This suggests that tablets or tablet fragments remained in the stomach until the later part of the night. Thus, diurnal effects may be more important than prandial effects in the evaluation of the kinetics of 5-ASA and its metabolites after peroral administration of enteric coated tablets.