Dissolution rate and transit times of technetium-99m DTPA-labeled tablets

In this study we demonstrate that the dissolution rate and gastroduodeno-cecal transit time of radiolabeled tablets of theophylline can be determined in vivo using technetium-99m (99mTc). Six healthy male volunteers ingested a tablet containing 300 mg of theophylline mixed with 3.7 MBq of [99mTc]DTPA. Anterior and posterior scintigraphic views of the abdomen were collected serially over 8 hr, after which a 200-ml solution containing 37 MBq of [99mTc] pertechnetate was ingested in order to visualize the contours of the stomach. The in vivo activity contained in the tablet was calculated from the scintigraphic views after correction of background activity, radioactive decay, and depth attenuation. The dissolution rate of [99mTc] DTPA was also measured in vitro and compared with the dissolution rate of theophylline. The results showed close dissolution rates between [99mTc]DTPA and theophylline in vivo (T1/2 184 min and 176 min, respectively), and a faster early dissolution rate of [99mTc]DTPA in vitro (T1/2 92 min versus 156 min for theophylline). The mean gastroduodenal and duodenocecal times were 72 +/- 25 min (m +/- s.d.) and 245 +/- 15 min, respectively. Scintigraphic imaging of labeled formulations with 99mTc present useful applications in pharmaceutics and pharmacology.