Radionuclide impurities in Therapeutic Dosages

[eh_carbaugh@ccmail.pnl.gov]

     A colleague has enquired as to what levels of radionuclide impurities 
     would be acceptable in radiopharmaceuticals of therapeutic dosage 
     magnitudes.  An alternate way of phrasing his question would be "what 
     level of unwanted absorbed dose or equivalent dose is acceptable due 
     to contaminating trace impurities in a radiopharmaceutical?"
     
     The application is that some radioisotopes for pharceuticals can be 
     chemically extracted from high level radioactive waste and might 
     contain impurities such as Cs-137, Pu isotopes, uranium isotopes, etc.
     
     Obviously the impurity should be a negligible contributor to the total 
     dose from the agent - but does anyone care to offer an opinion on what 
     that percentage or absolute magnitude might be?  I am unaware of any 
     pertinent FDA guidance or any other guidance on this particular 
     subject.
     
     Thanks in advance.
     
     Gene Carbaugh
     Pacific Northwest National Laboratory
     eh_carbaugh@pnl.gov