Radiolabelling of parenteral O/W emulsions by means of neutron activation

Abstract

Parenteral O/W emulsions containing lanthanide fatty acid derivatives were prepared. With regard to enhancing the incorporation efficiency of the neutron activatable excipients, the addition of the non-ionic co-emulsifier Solutol HS 15 ® proved to be most suitable. Comparing the different chain lengths of the fatty acids, the long chain fatty acid derivative lanthanide(tri)stearate seemed to be superior in strengthening the interfacial layer. After neutron activation, the physical and chemical stability of the irradiated formulations was evaluated. The chemical stability, indicated by the concentration of lyso phosphatidylcholine as the degradation product of the main emulsifier, was shown to be dependent on the irradiation time. By applying a neutron flux of 2.1×10 13 neutrons/cm 2 per s, the maximum should not rise above 60 s. The physical stability indicated by the particle size distribution was affected by the presence of the non-ionic co-emulsifier. Concerning the amount of radiation necessary for in vivo biodistribution studies the maximum load of Samarium fatty acid derivatives did not yield sufficient radioactivity levels. However, Europium derivatives could be shown to be suitable for in vivo studies.