Scintigraphic imaging and absorption of a 5-aminosalicylic acid enema in patients with ileorectal anastomosis

Ileorectal anastomosis (IRA) is a possible surgical treatment for hyperacute and drug-unresponsive forms of ulcerative colitis (UC). UC relapses in the rectal remnant usually are prevented by chronic administration of 5-aminosalicylic acid (5-ASA) in topical formulations. The relationships between intestinal absorption and pattern of luminal spread of 5-ASA enemas are still unknown in patients with IRA. We correlated the absorption of a 5-ASA enema with its spread in the distal bowel of patients with IRA as assessed by ^99mTc radioenema imaging. Methods: Eight patients with UC in remission and previous IRA received a therapeutic 50-mL 5-ASA enema labeled with ^99mTc-sulfer colloid. Absorbed 5-ASA and its major metabolite, acetyl 5-ASA, were measured in plasma, and dynamic images of radiolabeled enema were obtained for 6 h. The retrograde ileal spread (RIS) was determined and expressed as percentage of total enema radioactivity. Plasma levels of 5-ASA and acetyl 5-ASA were measured in six healthy volunteers after administration of the same enema volume with no radiolabeling. Results: The mean 5-ASA plasma level was 0.70 μg/mL (range 0.37-0.95 μg/mL) in patients and 0.96 μg/mL (range 0.78-1.16 μg/mL) in healthy volunteers (P = not significant), and the mean acetyl 5-ASA plasma levels were 0.89 μg/mL (range 0.44-1.19 μg/mL) and 0.84 μg/mL (range 0.51- 1.02 μg/mL), respectively (P = not significant). Radioenema imaging allows RIS assessment of patients with IRA. The mean value was 8.5% (range 2%-19.3%) of administered radioactivity, which correlated significantly with the total absorption of 5-ASA in the IRA group (P = 0.033, linear correlation test). Rectal wall contractions recognized by dynamic radioenema imaging were defined as a common cause of RIS episodes. Conclusion: In IRA patients, 5-ASA plasma levels were similar to those in healthy volunteers after administration in enema. Only part of a 50-mL 5-ASA enema reaches the ileum, and radiolabeled imaging shows the degree and number of these RIS episodes. The absorption of 5-ASA can increase in patients compared with healthy volunteers, in the presence of either occasional but significant ileal spread associated with postural factors and abdominal wall contraction or multiple moderate episodes of radioenema backdiffusion related to rectal wall motility.