In response to this public health crisis, the US Pharmacopeial Convention (USPC), in collaboration with FDA, manufacturers, and other stakeholders, revised the USP heparin monographs. The revision took place in two stages in order to better protect the US heparin supply and to help prevent future adulteration. To address the immediate public health risk, Stage 1 monograph revisions, completed in June 2008, consisted of validating and implementing proton nuclear magnetic resonance spectroscopy (1H NMR) and capillary electrophoresis (CE) procedures initially developed at FDA to detect OSCS. Stage 2 proposed monograph revisions include new Identification, Potency, and Impurity tests to better control the quality of heparin API.
Stage 1: Immediate responseThe Stage 1 monograph revisions of heparin sodium and heparin calcium incorporated FDA's analytical methods for identifying OSCS in heparin: 1 H NMR and CE. USPC laboratories validated these methods according to procedures outlined in General Information Chapter <1225> Validation of Compendial Procedures (3). In addition, USPC proposed appropriate system suitability criteria and specifications and developed two new reference standards (RS) to support the revised monographs: USP heparin sodium identification reference standard (RS) and USP heparin sodium system suitability RS.
The revised monographs were posted June 18, 2008, on the USPC website ( http://www.usp.org/) as Revision Bulletins and became official immediately. These monographs are referenced on the FDA website as well and have played an important role in controlling the quality of heparin API in the US (1).
Before posting the heparin Revision Bulletins, USPC solicited feedback from stakeholders by hosting two online meetings in spring 2008. Industry comments as well as submissions of new and improved analytical methods for characterization of heparin were critical in shaping the next stage of the monograph revision.
Stage 2: Comprehensive modernization
The USPC Heparin Ad Hoc Advisory Panel played a critical role in revising the heparin sodium monograph and updating the associated specifications. The panel consists of industry, academia, and regulatory experts from around the world and is advisory to USP's Biologics & Biotechnology Blood and Blood Products Expert Committee (BBP EC), which is part of USPC's Council of Experts. Working closely with FDA, panel members reviewed numerous submissions regarding new and improved analytical procedures for the characterization of heparin. These procedures first were evaluated for suitability as compendial methods, and when needed, further validation work was carried out.
Identification. Public feedback on the Stage 1 1H NMR method generally was positive, but commenters also recommended that USPC state a clear pass/fail criterion while expanding the procedure to cover the entire spectral range. The revised procedure covers a spectral window of at least 10 to–2 ppm and requires identification of four main heparin signals: H1 of N-acetylated glucosamine (GlcNAc)/N-sulfated glucosamine, 6S (signal 1), H1 of iduronic acid 2S (signal 2), H2 of N-sulfated glucosamine S (signal 3), and methyl H of GlcNAc (signal 4). In addition, clear acceptance criteria are spelled out to control both known and potential contaminants in heparin.
Based on public comments, the advisory panel recommended replacing the CE procedure with an anion-exchange high-performance liquid chromatography (HPLC) procedure that provides higher resolution between heparin and other impurities. Another consideration favoring the change is the wide availability of HPLC instruments.
The third Identification test that has been introduced is Antifactor Xa to Antifactor IIa Ratio. This ratio of activities is routinely used to characterize unfractionated heparin as well as to distinguish different forms of low-molecular weight heparins. For high-quality heparin, the ratio of anti-factor Xa to antifactor IIa should be not less than 0.9 and not more than 1.1. Manufacturers must perform all Identification tests because they serve orthogonal purposes.