DISTRIBUTION OF RADIOLABELED SUB-VISIBLE MICROSPHERES AFTER INTRAVENOUS ADMINISTRATION TO BEAGLE DOGS

The distribution and fate of intravenously administered microspheres in four size ranges were studied using Beagle dogs as an animal model. Administration of a dosage labeled with 200 μCi of cerium‐141 permitted γ‐camera observation. Animals were scanned upon dosing and again after 2 and 24 hr and 1, 2, and 4 weeks. The dogs were sacrificed after the 4‐week scan to quantitate the final distribution. Whole organs were excised and homogenized, and the total radioactivity was determined by analyzing representative samples in a well counter. Image analysis revealed no distribution differences between bolus administration and 30‐min infusion of doses of equal particle size and count. Spheres in the 25‐, 15‐, and 8‐μm ranges lodged by the time necessary to secure the first image (approximately 20 min) and did not undergo any observable relocation; the 3‐μm spheres appeared to be delayed in the lung. Well counting revealed that essentially all of the 25‐ and 15‐μm doses and the major part of the 8‐μm spheres were accounted for in the lungs after 4 weeks. Traces of the 8‐μm spheres also were found in the liver, spleen, heart, and kidneys. Of the 3‐μm spheres, over 75% were recovered in the liver, 17% in the spleen, 3% in the lung, and trace amounts in the kidneys and heart. Radioactivity in other organs and blood was negligible. Copyright © 1978 Wiley‐Liss, Inc., A Wiley Company