Acetylsalicylic acid-induced gastrointestinal bleeding determined by a 51Cr method on a day-to-day basis.

The daily gastrointestinal blood loss caused by plain and microencapsulated acetylsalicylic acid (ASA) tablets was compared. Fourteen healthy, male volunteers participated in a double-blind, cross-over study, lasting 38 days. Before drug administration a median gastrointestinal bleeding of 0.9 ml/24 h was observed. During oral intake of 1.5 g ASA twice a day for 5 days, an increased faecal blood loss was seen in all volunteers. The increase was significant for both plain and microencapsulated ASA (p less than 0.01). Plain ASA tablets, however, caused a greater faecal blood loss than the microencapsulated tablets (p = 0.05), maximum median levels being 6.2 ml/24 h and 3.9 ml/24 h, respectively. An optimal design of radiochromium studies for determination of drug-induced gastrointestinal blood loss is discussed.