In accordance with the Rules and Procedures of the 2010–2015 Council of Experts, the Monographs—Small Molecules 4 Expert Committee has revised the Primidone Tablets monograph. The purpose for the revision is to reconcile the Organic impurities test in Primidone Tablets monograph with the Organic impurities test in Primidone drug substance monograph as follows:

• Increase the acceptance criteria for Total impurities from NMT 0.3% to NMT 0.5%.
• Include two process impurities, 2-Cyano-2-phenylbutyramide and Phenylpropylprimidone along with their relative retention times for identification purposes. A note is included to specify that both the impurities are controlled in the drug substance monograph.  
• Increase the disregard limit (reporting threshold) from 0.025% to 0.05%.

This Primidone Tablets Revision Bulletin supersedes the currently official monograph. The Revision Bulletin will be incorporated in the First Supplement to USP 35–NF 30.

Should you have any questions, please contact Hari Ramanathan, M.S. (301-816-8313 or hr@usp.org).

• Download the Primidone Tablets Revision Bulletin