Bioavailability of digoxin tablets in patients with gastrointestinal dysfunction

In 47 patients with disorders of the gastrointestinal tract, the bioavailability of digoxin tablets was assessed by measuring the area under the serum concentration-time curve (AUC) after the oral administration of single 0.5 mg doses. In 13 or 14 patients who had undergone a previous ileal resection, in 10 of 10 patients with sprue and in 14 of 14 patients with a variety of disorders of the gastrointestinal tract, digoxin absorption was normal despite marked steatorrhea in many. A patient with extensive jejunal and ileal resection, and inflammation of the remaining small bowel, was the sole exception. Impaired digoxin bioavailabllity was found in five of nine patients who had undergone jejunoileal bypass procedures (bypass patients). A strong correlation was noted between the length of jejunum remaining in continuity and the AUC (r = 0.86, p < 0.01). Two of three bypass patients also showed decreased absorption of more rapidly dissolving tablets or an elixir. Digoxin bioavailability correlated significantly with 1 and 2 hour serum xylose levels but not with urinary xylose excretion, fecal fat or the Schilling test result. The findings are consistent with the role of the upper small bowel as the predominant site of digoxin absorption as well as the reserve function of the ileum in the event of jejunal dysfunction or bypass.