KI Again

["Thompson, Donald L. 827-0012" <DLT@FDADR.CDRH.FDA.GOV>]

If general use of KI by the public could result in a severe reaction..

Valid question onder the circumstances...empahsizes the danger of my trying to 
provide a brief answer to an inquiry.  The trade-offs are risk of contracting 
radiogenic thyroid carcinoma from unprotected exposure vs. the risk of severe 
fatal reaction to the protective drug.  Ignore for a minute the 25 rem 
threshold and the hundred other legitimate issues that could be raised.  Here 
are some numbers. From Sanders and Kathern's "Ionizing Radiation", the risk for 
induction of malignant thyroid tumors is 1.6-9.3 cases per million persons per 
year per rad.  From NCRP 55, based on FDA data (assumed under-reported) the 
rate of severe reactions (non-fatal) is between 1 x 10E-7 and 10 x 10E-7 at 
daily therapeutic levels of administration (300 mg).  The dose recommended for 
thyroid blocking is one-third of that (130 mg).  Only one death was reported to 
FDA in the seven years of data collection (from a 15 mg dose). Data was 
collected from 1969-1975.  More recent data from Chernobyl does not challenge 
the NCRP estimate.  As for 25 rem, admittedly it is low, but consistent with 
the EPA guidance for accident response.  More recent ICRP recommendations, 60. 
67 and 72, would increase that, if implemented.  Please address future comments 
to  DLT@FDADR.CDRH.FDA.GOV  Thank you.