2. Acetaminophen absorption test (AAT): Acetaminophen (20 mg/kg) will be given to patients. Serum acetaminophen will be determined by fluorescence polarization immunoassay. This assay uses a six-point calibration curve, and the detection limit is 4 µmol/L. The coefficient of variation is less than 5%. Estimation of the rate of gastric emptying was based on serum concentrations of acetaminophen in the blood samples collected. An algorithm that transforms serum concentrations of paracetamol into estimates of gastric emptying was applied. This algorithm adjusts for first-pass metabolism, unequal distribution and individual rate of elimination, and provides estimates for the percentage of meal emptied from the stomach as a function of time.