Patients being treated with low-molecular weight heparins-anticoagulants used to prevent and treat blood clots-are susceptible to potentially fatal adverse events known as heparin-induced thrombocytopenia (HIT). A new guidance document published by the US Food and Drug Administration (FDA) hopes to better warn patients of those risks through strengthened testing requirements.
As FDA explains in its new guidance document, Immunogenicity-Related Considerations for the Approval of Low Molecular Weight Heparin for NDAs and ANDAs, HIT is a dangerous side effect that affects between 0.2% and 1.3% of patients taking LMWH.
The condition causes the formation of abnormal antibodies, causing patients to develop fewer platelets than needed and resulting in the formation of blood clots.
Because LMWHs are frequently used in outpatient settings, FDA said it is "particularly important that applicants document how the risk of immunogenicity is assessed and managed" when submitting New Drug Applications (NDAs) or Abbreviated New Drug Applications (ANDAs).
That risk should be assessed through enhanced testing, FDA said, but sponsors should also take into account three factors to control for and characterize the risk of immunogenicity:
- the sameness of the active pharmaceutical ingredient (API) (ANDAs only)
- the impurities in the product that may impact on the association of the LMWH product with the chemokine PF4, as well as the size and charge of the complexes formed with PF4 (NDAs/ANDAs);
- the impurities in the product that could modify the detection, uptake, processing or presentation of the product (or the complexes it forms with PF4) to the immune system (NDAs/ANDAs)
The guidance does not recommend any particular methods for determining impurities, but says that any can be used so long as they are sufficiently sensitive to changes in the LMWH product.
However, "because bioanalytical characterization may be insufficient to confirm these three critical elements as they relate to immunogenicity considerations, we also recommend using in vitro and/or in vivo studies of the immune system to detect differences in the LMWH product as compared to its relevant reference product," FDA said.
For ANDAs, FDA recommended comparing the active ingredients of both products by assessing their physicochemical properties, source materials, biological and biochemical assays, in vivo pharmacodynamics profiles, mode of depolymerization, disaccharide building blocks, fragment mapping and sequences of oligosaccharide species.
"These criteria are highly sensitive to minor changes in manufacturing conditions and able to identify differences in a number of attributes among LMWH products found to meet relevant compendial standards," FDA explained.
Additional requirements for each method of comparison are explained within the guidance.
Focus on Impurities
The guidance also contains recommendations about how to assess impurities and immunogenicity risk for both NDAs and ANDAs, including supplemental applications.
As FDA explains:
"Heparin-induced thrombocytopenia (HIT) is mediated by antibodies to the LMWH-PF4 complex. The primary immunogenicity risk factor associated with LMWHs is thought to involve the interaction of the active ingredient with PF4 and the presence of impurities may affect the interaction of the LMWH with PF4. Therefore, the association of the LMWH with PF4, as well as the size and charge of the LMWH-PF4 complexes formed under specified conditions, should be assessed and compared to that of the relevant reference product."
"The association of the proposed LMWH and PF4 should be characterized at different ratios and concentrations" and assessed for immunogenicity, FDA added.
FDA said it recommends four approaches for characterization:
- testing the LMWH, as well as the unfractionated heparin source material and other raw materials for the presence of impurities (e.g., proteins, lipids, and nucleic acids)
- assessing the capacity of the manufacturing process to remove potential impurities
- characterizing the amount and nature of product impurities in the LMWH relative to those in its relevant reference product
- testing of the container closure systems to assess effects of extractables and leachables over the shelf life of the product
Other approaches may involve in vitro and in vivo immunological models, FDA said. All methods must be shown to be suitable for purpose.