Continuing to help ensure the identity, purity, and quality of heparin, the US Pharmacopeial Convention (USP) has revised
written and physical standards for the widely used blood thinner. In February 2009, USP released updated heparin standards
at the request of the US Food and Drug Administration in response to the 2008 public health crisis in which many patients
died as a result of adulterated heparin. A second phase of heparin monograph revisions is reflected in the newly posted standards
(1). These developments and new analytical characterization tools for heparin were discussed by scientists and regulators
at the Third International Heparin Workshop held at USP headquarters in Rockville, Maryland, July 27–28, 2009 (2).
The workshop, cosponsored by USP, the British National Institute of Biological Standards and Control (NIBSC), and the European
Directorate for the Quality of Medicines (EDQM), reflected the global nature of both the problem of adulteration and the resources
available to combat it. Attendees came from more than 17 countries. Workshop deliberations focused on safeguarding heparin
supply, pharmacopeial updates, and progress on biosimilar low-molecular-weight heparins (LMWHs).
In early 2008, FDA confirmed reports of adverse health events associated with the use of heparin that had been contaminated
with oversulfated chondroitin sulfate (OSCS) originating in China (3, 4). In June 2008, USP responded to the heparin crisis
by revising its heparin sodium and heparin calcium monographs. Stage-1 monograph revision incorporated FDA's analytical methods
for the identification of OSCS in heparin: proton nuclear magnetic resonance spectroscopy (1H NMR) and capillary electrophoresis (CE). Other pharmacopeias followed suit.
Although this short-term measure prevented contaminated heparin from entering the supply chain, USP and stakeholders realized
that a thorough modernization of the existing monographs would be needed to ensure the continuing quality of heparin. USP
has since undertaken a second stage of revisions to the heparin sodium monograph, adding new identification, potency, and
impurity tests that better control the quality of heparin active pharmaceutical ingredient (API). The European Pharmacopoeia
(EP) and Japanese Pharmacopoeia (JP) also are taking a stepwise approach to revising their heparin monographs.
LMWHs are defined as heparin salts that have an average molecular weight of < 8000 Da and for which at least 60% of all chains
have a molecular weight of < 8000 Da. LMWHs are prepared from unfractionated heparin (UFH) by various chemical or enzymatic
depolymerization processes. Thus, the starting material of LMWHs is of biological origin, and the manufacturing process defines
the characteristics of the drug substance. Because the manufacturing process does not necessarily remove all impurities present
in UFH, manufacturers should ensure that the starting material complies with the latest regulatory requirements.
Table I: Stage-2 revisions of heparin monographs from world pharmacopeias.
Several licensed LMWHs differ in their source material, manufacturing process, pharmacokinetic/pharmacodynamic properties,
and therapeutic indications. The development of biosimilar LMWH products has increased globally during the past decade. In
anticipation of the arrival of more biosimilar LMWHs in the near future, workshop participants discussed the regulatory framework
for follow-on biologic products. Additional topics included regulatory issues (e.g., immunogenicity) and analytical tools
aimed at demonstrating comparability to licensed products.
Challenges of heparin characterization
Heparin is structurally the most complex member of the glycosaminoglycan (GAG) family of polysaccharides, which also includes
chondroitin sulfate, dermatan sulfate, and keratin sulfate. Commercially available heparin in the US is derived mostly from
porcine intestinal mucosa. Selectivity and yield emphasis in the purification steps affect the impurity profile of the resulting
API with regard to common impurities such as dermatan sulfate and residual solvents. Because the different GAGs coexist in
their natural sources, it is not uncommon to obtain GAG preparations contaminated with a structurally similar polysaccharide.
Because of this complex milieu, the challenges are to sufficiently quantify process impurities and naturally occurring impurities
that are not cleared by the purification steps and to concurrently detect any potential contaminants intentionally added to
heparin. Workshop partcipants agreed that the quality of crude heparin can only be achieved by complete traceability and good
manufacturing practices (GMPs) throughout the manufacturing life cycle and by supplier qualification.