Acrylic microspheres in vivo. I. Distribution and elimination of polyacrylamide microparticles after intravenous and intraperitoneal injection in mouse and rat.

Microspheres of 14C-labeled highly cross-linked polyacrylamide (mean diameter 0.25-0.30 micron) have been prepared by emulsion polymerization. The label was introduced in the polymer via the cross-linking monomer. N,N'-[14C]methylenebisacrylamide. The microparticles were used to follow qualitatively and quantitatively the distribution and the fate of polyacrylamide in mouse and rat after i.v. and i.p. injection. The polyacrylamide particles are rapidly cleared from the circulation (t 1/2 in rat approximately 40 min) by macrophages of the reticuloendothelial system. They are mainly (about 80%) found in the liver and spleen both after i.v. and i.p. injection (4.1 mg given totally to mice weighing 20-25 g). They can also be detected early (1 hr after i.v. injection) in the bone marrow, and particle aggregates are also initially found in the lungs, although no respiratory problems were noted. After about 16 weeks, the radioactivity rapidly decreases in the liver and spleen, with t 1/2 10 to 14 weeks and 15 to 24 weeks, respectively, depending on the route of administration. Radioactivity in the gut and gut walls detected 2 months after injection suggests that the polyacrylamide is slowly metabolized. No toxic effects-apart from transient hepatospleenomegaly-were detected in mice 45 weeks after they were given a total of 9.8 mg of polyacrylamide.