RADIOLABELING OF POLYMER MICROSPHERES FOR SCINTIGRAPHIC INVESTIGATIONS BY NEUTRON-ACTIVATION .4. A PHARMACOSCINTIGRAPHY STUDY OF COLON-TARGETED EUDRAGIT RS-SULFAPYRIDINE MICROSPHERES IN HUMAN VOLUNTEERS

Dosage forms containing sulphapyridine have been administered to a gro up of five human subjects in a two-part combined pharmacokinetic and g amma scintigraphic study. In one portion of the study, subjects were a dministered enteric-coated capsules containing sulphapyridine powder a nd Tc-99m-labelled ion-exchange resin. In the second portion of the st udy, the subjects were administered enteric-coated capsules containing Sm-153-labelled sustained-release sulphapyridine-Eudragit RS microsph eres. In both cases, the enteric-coated capsules were designed to deli ver their contents into the caecum or ascending colon. Following capsu le disintegration, the residence time of 50% of the radiolabelled micr ospheres in the ascending colon was 8.4+/-2.0 h (n = 5), which did not differ significantly from the residence time of 50% of the radiolabel led ion-exchange resin (7.2+/-1.9 h, n = 5). Pharmacokinetic analysis indicated a prolongation of drug release from the microsphere formulat ion. The bioavailability of sulphapyridine from the microspheres relat ive to the non-encapsulated drug powder was 41.3+/-12.7% (n = 4). The reason for the reduction in drug absorption from the microsphere formu lation was unclear although several theories are proposed.