Distribution and Elimination of Poly (methyl methacrylate) Nanoparticles After Subcutaneous Administration to Rats

□ Poly (methyl [l-14C]methacrylate) nanoparticles were injected subcutaneously into rats. Almost all of the radioactivity stayed at the injection site. After an initial urinary and fecal excretion of ~ 1% of the administered dose per day, the rate of elimination dropped to a low level (~ 0.005%/day via the feces and ~ 0.0005%/day via the urine) within 70 days. After 200 days, the fecal elimination increased exponentially until a > 100-fold increase was observed after 287 days in one rat. After this time, a tendency for an increase in fecal elimination was also observed in the other animals, and the radioactivity in all organs and tissue increased by ~ 100 times in all animals in comparison with the organ radioactivity determinations at earlier times.