The effect of buffering of acetylsalicylic acid on dissolution,absorption, gastric pH and faecal blood loss

A high-buffered experimental acetylsalicylic acid (ASA) tablet designed to be swallowed intact and a conventional low-buffered ASA tablet were compared in vitro with regard to dissolution and buffering and in vivo with regard to absorption, intragastric buffering and tendency to cause gastrointestinal bleeding.high-buffered tablet was dissolved in vitro within 3 min. In vivo the tablet raised the intragastric pH to a minimum value of 7 and reached a maximal plasma concentration after 20–30 min. The low-buffered tablet dissolved more slowly and did not raise the pH in vitro above 2. In vivo the tablet raised the intragastric pH to 4.5 and a maximal plasma concentration of salicylate was obtained after 90 min. The high-buffered tablet reduced the daily faecal blood loss by 50% compared to the low-buffered tablet.It can be concluded that the high-buffered tablet was more rapidly dissolved and faster absorbed than the low-buffered tablet. The reduced gastrointestinal bleeding found with the high-buffered tablet is probably due to an adequate in vivo buffering.