Time-dependent distribution and excretion of radiolabelled, semipermeable, stable magnetic microcapsules

The time-dependent excretion and potential body retention of magnetic polyethyleneimine (PEI) microcapsules, methylated with [14C]methyl iodide have been investigated after intragastric administration to mice. Gastric emptying was rapid but about 10% of the administered dose was still present in the stomach after 6 h; the number of microcapsules within the small intestine remained approximately constant over 1-6 h. Excretion of microcapsules in the faeces was virtually complete (98.7% excretion within 72 h), with small amounts of radioactivity excreted via the urine or as [14C]CO2. There was no detectable adsorption or retention of microcapsules within the body as measured by either a whole-body autographic study or by direct quantitation of tissue radioactivity.