The Immunogenic Potential of Generic Version of Low-Molecular-Weight Heparins May Not be the Same as the Branded Products
Jawed Fareed, PhD, DSc, Rodger L. Bick, MD, PhD, Gundu Rao, PhD, Samuel Z. Goldhaber, MD, Arthur Sasahara, MD, Harry L. Messmore, MD, Debra A. Happensteadt, PhD, and Andrew Nicolaides, MD, on behalf of the IACATH, IUA, SASAT, and NATF*
Heparin-induced thrombocytopenia (HIT) is a catastrophic adverse reaction associated with the use of heparins and related products. Although the incidence of HIT with low-molecularweight heparins (LMWHs) is much lower than with unfractionated heparin (UFH),1 these agents are capable of triggering immunogenic responses in 10% to 20% of the patients treated for different indications. The generation of these antibodies depends on the dosage, duration of treatment, patient population, and underlying comorbidities. Differences in the immunogenic responses among different branded LMWHs have been noted. These differences are due to the structural composition of the LMWH and the interactions with endogenous platelet factor 4 (PF4) and other proteins.
Low-molecular-weight heparins have been differentiated on the basis of several biophysical, biochemical, and pharmacologic properties. These differences translate into their safety and efficacy profiles in a given clinical indication. Therefore, the United States Food and Drug Administration (FDA) and other regulatory bodies consider each of the commercially available LMWHs as a distinct drug and require clinical validation for the approval of each of these in specific indications. The introduction of generic versions of the branded LMWHs has challenged the regulatory bodies to develop specific guidelines for their approval. The current guidelines for generic drug approval are not adequate because of the complex nature of the LMWHs due to biologic origins and chemical modifications of a polycomponent mixture of glycosaminoglycans.
Although the incidence of HIT is rare with the use of LMWHs and heparinomimetics such as fondaparinux and idraparinux when used for prophylactic and therapeutic indications, these agents are capable of generating antibodies to heparin-PF4 complex, which are measurable by using immunologic methods. 2-11 The relative prevalence of these antibodies is method-dependent owing to different capturing probes. Moreover, the relative proportion of antibody subtypes (immunoglobulin G, A, and M) differ from product to product.12-14 Up to 20% of the patients treated with LMWHs generate these antibodies. The pathophysiologic role of these antibodies remains unknown at this time.15-20 However, this immunogenic response is comparable to autoimmune responses observed in the case of the antiphospholipid syndrome. Additional data are needed to identify the role of these antibodies in various pathologic states and their impact on clinical outcomes.
The FDA has been visionary in identifying the immunogenicity of LMWHs as an important criterion to differentiate and demonstrate the bioequivalence of generic LMWHs to the branded products. The agency has made a determination that the immunogenic responses of LMWHs occur because of the interactions of the components of the generic products with PF4 and other proteins, that result in the formation of complexes that lead to an immunogenic response. Therefore, if a generic product has identical composition and similar proportion of the oligosaccharide components as the branded product, then the generic product would exhibit a similar quantitative and qualitative immunogenic profile. Such a bioequivalence can only be demonstrated in well-designed, population-balanced clinical trials that include critically ill patients with multiple pathogenic etiologies. The FDA is to be commended for this very clear directive. This underscores the concerns on the use of biologics that have multiple components and mechanisms of action.
Although the generic LMWHs may exhibit similar molecular profile and anti-factor Xa potency, some of the currently available generic versions of LMWHs have been found to differ in their biochemical and pharmacologic profiles.21 Therefore, the additional recommendation to profile these agents for other biologic actions and their interactions with cells beyond the immunogenic profiling should also be taken into consideration to assure therapeutic equivalence. As the different regulatory and professional organizations are moving ahead in developing recommendations for the therapeutic and generic interchange of these drugs in different indications, the FDA’s action to require immunogenic profiling of these drugs is not only timely but also prudent in establishing approval guidelines which will have an International impact.
Heparin and LMWHs are also capable of binding to several other endogenous proteins. It is likely that these interactions can also result in the generation of neoepitopes. The physiologic implications of such responses are not known. Most of the immunogenic response data currently available are based on the use of 2 methods that use enzyme-linked immunosorbent assay.22With the advances in technology, several other methods have recently become available. Therefore, it is important to have standardized methods to compare the immunogenic potential using valid methodologies with particular reference to the specific antibodies to be profiled. At the present time, the immunogenic profiling is focused on the antibodies that are generated against the PF4 neoantigen formed upon complexation of heparin oligosaccharides and PF4.
The International Academy of Clinical and Applied Thrombosis and Hemostasis (IACATH), the International Union of Angiology (IUA), the South Asian Society of Atherosclerosis and Thrombosis (SASAT), and the North American Thrombosis Forum (NATF) will review and consider endorsing this requirement in conjunction with the white paper that is currently being prepared on the International Summit on Generic Antithrombotic drugs that was held in New Delhi under their auspices on October 12, 2007. This white paper will be published in the journals of the sponsoring societies and posted on their respective Web sites
References
1. Walenga JM, Prechel MM, Jeske WP, Bakhos M.
Unfractionated heparin compared with low molecular
weight heparin as related to heparin-induced thrombocytopenia.
Curr Opin Pulmon Med. 2005;11:385-391.
2. Warkentin TE, Levine MN, Hirsh J, et al. Heparininduced
thrombocytopenia in patients treated with lowmolecular-
weight heparin or unfractionated heparin.
N Engl J Med.. 1995;332:1330-1335.
3. Amiral J, Peynaud-Debayle E, Wolf M, Bridey F, Vissac
AM, Meyer D. Generation of antibodies to heparin-PF4
complexes without thrombocytopenia in patients treated
with unfractionated or low-molecular-weight heparin.
Am J Hematol. 1996;52:90-95.
4. Bauer TL, Arepally G, Konkle BA, et al. Prevalence of
heparin-associated antibodies without thrombosis in
patients undergoing cardiopulmonary bypass surgery.
Circulation. 1997;95:1242-1246.
5. Pouplard C, May MA, Iochmann S, et al. Antibodies to
platelet factor 4-heprin after cardiopulmonary bypass in
patients anticoagulated with unfractionated heparin or a
low molecular weight heparin: clinical implications for
HIT. Circulation. 1999;99:2530-2536.
6. Lindhoff-Last E, Eichler P, Stein M, et al. A prospective
study on the incidence and clinical relevance of heparininduced
antibodies in patients after vascular surgery.
Thromb Res. 2000;97:387-393.
7. Prechel M, Bano A, Drenth AF, Messmore HL, Walenga
JM. Assay selection and interpretation for laboratory
testing of heparin-induced thrombocytopenia: diagnostic
implications. Blood. 2001;98:36a.
8. Gruel Y, Pouplard C, Nguyen P, et al, the French
Heparin-Induced Thrombocytopenia Study Group.
Biological and clinical features of low-molecular-weight
heparin-induced thrombocytopenia. Br J Haematol.
2003;121:786-792.
9. Francis JL, Palmer GP III, Moroose R, Drexel A.
Comparison of bovine and porcine heparin in heparin
antibody formation after cardiac surgery. Ann Thorac
Surg. 2003;75:17-22.
10. Gluckman TJ, Segal JB, Fredde NL, et al. Incidence of
anti-platelet factor 4/heparin antibody induction in
patients undergoing percutaneous coronary revascularization.
Am J Cardiol. 2005;95:744-747.
11. Warkentin TE, Maurer BT, Aster RH. Heparin-induced
thrombocytopenia associated with fondaparinux. N Engl
J Med. 2007;356:2653-2654.
Ahmad S, Untch B, Haas S, et al. Differential prevalence
of anti-heparin-PF4 immunoglobulin subtypes in patients
treated with clivarin and heparin: implications in the HIT
pathogenesis. Mol Cell Biochem. 2004;258:163-170.
13. Ahmad S, Haas S, Hoppensteadt DA, et al. Differential
effects of clivarin and heparin in patients undergoing hip
and knee surgery for the generation of anti-heparin-platelet
factor 4 antibodies. Thromb Res. 2003;108:49-55.
14. Ahmad S, Bacher P, Lassen MR, et al. Investigations of
the immunoglobulin subtype transformation of antiheparin-
platelet factor 4 antibodies during treatment with
a low-molecular-weight heparin (Clivarin) in orthopedic
patients. Arch Pathol Lab Med. 2003;127:584-588.
15. Chilver-Stainer L, Lämmle B, Alberio L. Titre of antiheparin/
PF4-antibodies and extent of in vivo activation of
the coagulation and fibrinolytic systems. Thromb Haemost.
2004;91:276-82.
16. Mattioli AV, Bonetti L, Sternieri S, Mattioli G. Heparininduced
thrombocytopenia in patients treated with unfractionated
heparin: prevalence of thrombosis in a 1 year
follow-up. Ital Heart J. 2000;1:39-42.
17. Williams RT, Damaraju LV, Mascelli MA, et al. Antiplatelet
factor 4/heparin antibodies. An independent
predictor of 30-day myocardial infarction after acute coronary
ischemic syndromes. Circulation. 2003;107:2307-12
18. Fareed J, Iqbal O, Nader H, et al. Generic low molecular
weight heparins: a significant dilemma. Clin Appl
Thromb Hemost. 2005;11:363-366.
19. Hoppensteadt D, Jeske W, Ahsan A, Walenga J, Fareed J.
Biochemical and Pharmacologic Profile of Defined
Molecular Weight Fractions of Heparin. Sem Throm
Hemost. 1993;19:12-19.
20. Untch B, Ahmad S, Jeske W, et al. Prevalence, isotype,
and functionality of antiheparin-platelet factor 4 antibodies
in patients treated with heparin and clinically
suspected for heparin-induced thrombocytopenia: the
pathogenic role of IgG. Thromb Res. 2002;105:117-123.
21. Jeske WP, Ackerman P, Drenth A, Walenga J, Bakhos M.
Generic versions of branded low molecular weight heparins
can be differentiated in biologic and pharmacologic assays.
J Thromb Haemost. 2007;5(suppl 2):P-M-647.
22. Izban KF, Lietz HW, Hoppensteadt DA, et al. Comparison
of two PF4/heparin ELISA assays for the laboratory
diagnosis of heparin-induced thrombocytopenia. Semin
Thromb Hemost. 1999;25(suppl 1):51-56.
