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

Ileorectal anastomosis (IRA) is a possible surgical treatment for hyperacut e and drug-unresponsive forms of ulcerative colitis (UC). UC relapses in th e rectal remnant usually are prevented by chronic administration of 5-amino salicylic acid (5-ASA) in topical formulations. The relationships between i ntestinal absorption and pattern of luminal spread of 5-ASA enemas are stil l unknown in patients with IRA. We correlated the absorption of a 5-ASA ene ma with its spread in the distal bowel of patients with IRA as assessed by Tc-99m radioenema imaging. Methods: Eight patients with UC in remission and previous IRA received a therapeutic 50-mL 5-ASA enema labeled with Tc-99m- 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 lev el was 0.70 mu g/mL (range 0.37-0.95 mu g/mL) in patients and 0.96 mu g/mL (range 0.78-1.16 mu g/mL) in healthy volunteers (P = not significant), and the mean acetyl 5-ASA plasma levels were 0.89 mu g/mL (range 0.44-1.19 mu g /mL) and 0.84 mu g/mL (range 0.51-1.02 mu g/mL), respectively (P = not sign ificant). Radioenema imaging allows RIS assessment of patients with IRA. Th e 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 gro up (P = 0.033, linear correlation test). Rectal wall contractions recognize d by dynamic radioenema imaging were defined as a common cause of RIS episo des. 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 an d number of these RIS episodes. The absorption of 5-ASA can increase in pat ients compared with healthy volunteers, in the presence of either occasiona l but significant ileal spread associated with postural factors and abdomin al wall contraction or multiple moderate episodes of radioenema backdiffusi on related to rectal wall motility.