Inhibitory Effects of Metal Ions in Radiopharmaceuticals on PCR Amplification for Rapid Sterility Tests.

Most radiopharmaceuticals are administered as injectable preparations and are therefore subject to sterility testing. Sterility testing usually requires a 14-d incubation period, which poses a significant challenge for short-lived radiopharmaceuticals because testing must be performed retrospectively. Advances in science and technology have led to the development of various rapid microbial detection methods, one of which is the nucleic acid amplification technique employing PCR. However, PCR is known to be inhibited by a variety of metal ions, and radiopharmaceuticals frequently contain metal ions as radionuclides or as additives, raising concerns regarding false-negative results. In the present study, PCR was performed in the presence of metal radionuclides and additives (ZnCl2, InCl3, LuCl3, YCl3, SnCl2, GaCl3, CuCl2, TlCl, and ZrOCl2) used in radiopharmaceuticals. Lutetium (Lu) and yttrium (Y) exhibited particularly strong PCR inhibitory ability across all enzyme systems tested, while zirconium (Zr) exhibited strong but markedly system-dependent inhibition, showing negligible inhibition with one of the enzyme systems tested. Addition of the chelating agent 2,2',2″,2‴-(1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid to Lu-containing samples restored amplification activity, suggesting that radiopharmaceuticals in their chelated form are unlikely to inhibit PCR. Furthermore, when we conducted an analysis using a mock sample that closely resembled the actual radiopharmaceutical, we observed PCR inhibition that appeared to be caused by excipients at concentrations higher than those of the radionuclide, suggesting that pretreatment may be necessary depending on the formulation.