Heparin-induced thrombocytopenia successfully treated with fondaparinux

Fondaparinux: does it cause HIT? Can it treat HIT?

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated prothrombotic disorder triggered by PF4-binding polyanions, usually heparin. The pentasaccharide anticoagulant, fondaparinux, despite its negative charge and structural similarity to heparin, does not usually promote antibody binding to PF4 (owing to absent/weak 'cross-reactivity'). Thus, despite its ability to trigger anti-PF4/heparin antibodies ('immunogenicity'), fondaparinux has low - but not zero - risk of inducing HIT de novo, or of exacerbating HIT when antibodies are already present. Indeed, despite rare reports of fondaparinux-induced HIT, this 'dissociation' between immunogenicity and cross-reactivity suggests that fondaparinux should be effective in treating HIT, as supported by several observational studies. An emerging issue: will clinicians accept this favorable experience of fondaparinux for treating HIT when a lack of randomized trials will hinder regulatory approval for this indication?

Fondaparinux and the management of heparin-induced thrombocytopenia: the journey continues

OBJECTIVE

To review the available literature addressing the role of fondaparinux in the management of heparin-induced thrombocytopenia (HIT).

DATA SOURCES

Primary articles were identified by a MEDLINE search (2004-June 2009) of English-language literature using the MeSH headings fondaparinux, heparin, low-molecular-weight heparin, and thrombocytopenia. Relevant consensus guidelines (2006-June 2009) were also identified.

STUDY SELECTION AND DATA EXTRACTION

All published studies and case reports, as well as relevant consensus guidelines, evaluating the use of fondaparinux for the management of HIT were included.

DATA SYNTHESIS

The role of fondaparinux in the management of HIT is a therapeutic controversy challenging clinicians today. An open-label, prospective pilot study of 7 patients with acute HIT supports fondaparinux as an alternative anticoagulant. Additionally, a total of 12 patients with HIT from a larger case study and retrospective cohort were successfully treated with fondaparinux. Much of the supporting data exists in the form of case reports, each demonstrating normalization of platelet counts without any evidence of new thrombosis. The differences in clinical scenarios as well as the role and dose of fondaparinux make interpretation of these reports difficult. Three case reports have been published raising concerns regarding fondaparinux causing or failing to manage HIT appropriately. However, common weaknesses such as small sample sizes and nonuniform definitions of HIT limit the usefulness of these findings. The updated American College of Chest Physicians consensus guidelines now recognize fondaparinux as an option in the management of HIT; however, the level of evidence supporting this is of low quality. The use of fondaparinux as a bridging agent between direct thrombin inhibitor and warfarin therapy has been proposed. A recently published case report gives support to this approach.

CONCLUSIONS

Controlled clinical trials evaluating the use of fondaparinux in the management of HIT need to be completed before this therapy can be routinely recommended.