ACTIVATED-CHARCOAL AS A POTENTIAL RADIOACTIVE MARKER FOR GASTROINTESTINAL STUDIES

The scintigraphic measurement of colonic transit is currently performe d using In-111 ion exchange resin pellets delivered to the colon in a capsule coated with a pH sensitive polymer, methacrylate, which dissol ves in the distal ileum. However, in the USA, this requires an investi gational drug permit. Our aim was to evaluate the in vitro binding cha racteristics of activated charcoal in milieus that mimicked gastric an d small intestinal content. The in vitro incubation of activated charc oal was performed with (NaTcO4)-Tc-99-O-m, Tc-99(m)-DTPA, (InCl3)-In-1 11, In-111-DTPA, (TlCl)-Tl-201 and Ga-67-citrate in the pH range 2-4 a nd pH 7.2 at 37 degrees C. We estimated the association of radiopharma ceuticals with the activated charcoal over a 3 h in vitro incubation. With the exception of Ga-67-citrate, the association of activated char coal with the other radiopharmaceuticals was approximately 100% throug hout the 3 h incubation. In conclusion, activated charcoal appears to adsorb avidly with common radioisotopes, and appears promising as an a lternative to resin ion exchange pellets used for the measurement of g astrointestinal transit by scintigraphy. ((C) 1998 Chapman & Hall Ltd. ).