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In vivo evaluation of 99mTc-DTPA and 99mTc-sulphur colloid as tracers in colonic drug delivery systems using gamma scintigraphy in volunteers.

PURPOSE
The suitability of 99mTc-diethylenetriaminepenta- acetic acid (DTPA) and 99mTc-sulphur colloid (99mTc-SC) as tracers in gamma scintigraphy for the evaluation of colon-specific drug delivery systems was assessed in healthy volunteers.


METHOD
Sodium chloride core tablets containing either 99mTc-DTPA or 99mTc-SC were prepared and compression coated with two different quantities of guar gum. The compression-coated tablets were subjected to gamma scintigraphic studies for colonic drug delivery in healthy human volunteers.


RESULTS
The tablets containing 99mTc-DTPA did not release the tracer in stomach and small intestine, and on entering the colon disintegrated completely whereas the tablets containing 99mTc-SC remained intact in stomach, small intestine and in colon as well. The study showed that DTPA is a suitable tagging agent for 99mTc in the evaluation of guar gum based colonic drug delivery systems containing water-soluble drugs.


CONCLUSION
In the present investigation guar gum was applied externally as a compression coat over the radiolabelled core. Since the core consisted of water-soluble material (sodium chloride), it is possible that the release of the tracer from the 99mTc-DTPA containing formulations is a combined effect of enzymatic action and diffusion of the salt. The failure of disintegration of 99mTc-SC containing formulations might be due to its interference with the disintegration or the part diffusion observed with 99mTc-DTPA cores. The results of the study showed that DTPA is a suitable tagging agent for 99mTc in the evaluation of colonic drug delivery systems containing water-soluble drugs by gamma scintigraphy.