Design of the randomized crossover study. Before randomization, ET patients on enteric-coated aspirin 100 mg once daily were visited twice and randomized at visit 1 to computer-generated sequences of 7-day treatments that included: enteric-coated aspirin 200 mg daily, enteric-coated aspirin 100 mg twice daily, and plain aspirin 100 mg once daily, with 7-day washouts between each treatment. Blood and urine collections were performed on the last day of treatment or washout visits. EC indicates enteric-coated.