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Tina S. Morris, PhD, is vice president of Biologics & Biotechnology at United States Pharmacopeia (USP)
USP optimizes identification tests and impurities procedures.
Adverse health events associated with the use of adulterated or counterfeit heparin prompted the Centers for Disease Control and Prevention (CDC) and FDA to begin a nationwide investigation in January 2008 of the commonly used blood-thinning drug. FDA confirmed that serious injuries and deaths had been associated with the use of heparin manufactured with an API sourced from China (1). During this investigation, FDA scientists also identified a previously unknown contaminant, oversulfated chondroitin sulfate (OSCS), in the heparin (2).
Working with FDA, manufacturers, and other stakeholders, the US Pharmacopeial Convention (USP) responded to this public health crisis by embarking on a revision of its public quality standards for heparin to enable the identification of OSCS and related contaminants. USP, a scientific nonprofit organization, develops standards that test for the identity, strength, quality, and purity of medicines, including biologic drugs like heparin. Published in its compendia, US Pharmacopeia and National Formulary (USP–NF), USP's documentary or written standards (i.e., monographs) are developed for individual drugs and their ingredients.
Since 2008, revisions of the heparin standards have taken place in three stages in order to better protect the US supply in a timely manner and help prevent future adulteration (see Table I). To address the immediate public health risk posed in 2008, Stage 1 monograph revisions 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 monograph revisions included new identification, potency, and impurity tests to better control the quality of heparin API (3). The Stage 2 revised heparin monographs became official on October 1, 2009 (4).
Table I: Changes to heparin sodium monograph during Stage 1 through Stage 3 revisions.
Stage 3 revisions focus on further optimization of identification tests and a protein impurities procedure as well as the introduction of brand new molecular weight determination and nucleotidic impurities procedures. To decide on specifications for the new molecular weight determination and impurities tests, USP engaged stakeholders in two round-robin studies. The studies were designed to gather feedback on the proposed procedures prior to their publication in Pharmacopeial Forum—USP's free-access, online publication for posting and receiving public comments on standards in development. Round-robin participants were requested to test their in-house heparin API batches using the proposed procedures. Final acceptance criteria for the tests were based on the batch data received during the studies.
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Heparin Sodium monograph Stage 3—specifics
Immediately after the implementation of the Stage 2-revised Heparin Sodium monograph, USP collaborated with stakeholders and FDA to further strengthen the standard and help ensure continued access to heparin of good and acceptable quality. USP's third stage of revisions aimed to optimize and reinforce the Heparin Sodium monograph against OSCS and process impurities.
The USP Unfractionated Heparin Expert Panel played a crucial role in modernizing the Heparin Sodium monograph and updating the associated specifications. The panel consists of industry, academic, and regulatory experts from around the world and is advisory to USP's Monographs—Biologics & Biotechnology 1 Expert Committee (Monographs-BB1 EC), which is responsible for establishing and updating heparin standards and is part of USP's Council of Experts. With FDA input, panel members reviewed submissions regarding new and improved analytical procedures for the characterization of heparin. These procedures first were evaluated for suitability as compendial methods; when needed, further validation work was carried out.
Identification. Public feedback on the Stage 2 1H NMR procedure generally was positive, but commenters did recommend minor modifications to the experimental procedure. These include the option of adding ethylenediaminetetraacetic acid (EDTA), reduced trimethylsilylpropionic acid sodium salt (TSP) concentration in a sample solution, as well as adjustments to the temperature range, acquisition time, and longer delay time. The major change was the reduced percentage—0.3% (w/w) instead of 1% (w/w)—of OSCS in system suitability solution to ensure a higher sensitivity of the method for OSCS.
Also based on public comments, the expert panel optimized and validated an improved anion-exchange high-performance liquid chromatography (HPLC) procedure that provides a shorter run time, higher resolution between heparin and dermatan sulfate, and improved sensitivity for impurities.
The third identification test that has been introduced is molecular weight determinations. The molecular weight profile of heparin is an intrinsic property that depends on the starting material and the manufacturing process. The resulting molecular weight distribution of finished heparin API in turn influences its potency, its ease of neutralization by protamine sulfate, and its propensity to interact with plasma proteins (e.g., platelet factor 4, leading to heparin-induced thrombocytopenia [HIT]). Therefore, the molecular weight distribution of heparin API could be used to ensure manufacturing process consistency as well as the safety of heparin API.
Nucleotidic impurities and protein impurities. A new quantitative HPLC-based method has been added to control residual DNA in heparin. A quantitative Lowry method replaced the old turbidity test for protein impurities during Stage 2 revision. The improved procedure proposed in Stage 3 incorporates an additional step for removing interfering substances from heparin sample solution. A lower acceptance limit is proposed for both impurities procedures based on the batch data received during the round-robin studies.
The proposed revisions to the Heparin Sodium monograph—which include the two optimized identification procedures, the new molecular weight determinations procedure, the optimized method for protein impurities, and the new method for nucleotidic impurities—will be published in Pharmacopeial Forum 38(6) (November–December 2012). Comments will be accepted until Jan. 31, 2013. After review of the comments and further consideration by the monographs-BB1 EC, the Heparin Sodium Monograph is expected to be approved and become official in USP 37–NF 32. Comments on the standards should be sent to email@example.com.
In light of the significant changes introduced in the Stage 3 revisions, USP will continue to update stakeholders in a timely manner about the current status of the monograph revisions and ensure that sufficient time is provided for a public evaluation of the procedures, specifications, and implementation date. Working in close partnership with FDA, industry, and other stakeholders, USP will work to ensure that revisions to the monographs are suitable and will support the overall framework for delivering a safe and effective supply of medicines for patients.
Anita Y. Szajek, PhD, is principal scientific liaison, and Tina S. Morris, PhD, is vice-president of biologics & biotechnology, both at the US Pharmacopeial Convention (USP), firstname.lastname@example.org.
1. FDA, Information on Heparin (2009), www.fda.gov/cder/drug/infopage/heparin/default.htm, accessed Jan. 29, 2009.
2. M. Guerrini et al., Nat. Biotech., 26 (6), 669–675 (2008).
3. USP, USP 35–NF 30, Heparin Sodium monograph, pp. 3403–3406 (USP, Rockville, MD).
4. A. Szajek et al., Pharm. Tech., 33 (3), 136–137 (2009).