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Combined Trials: PF4/H-reactive IgG Antibodies

— Fondaparinux Enoxaparin p = 0.86

Days from first injection

Days from first injection

Days from first injection

FIGURE 4 Anti-PF4/heparin antibody formation in patients receiving fondaparinux or enoxaparin after orthopedic surgery (current status analysis). Data are combined for patients undergoing knee and hip replacement. (Left) Anti-PF4/heparin antibodies of IgG class. There is no significant difference between the study drug groups (p = 0.86). (Right) All anti-PF4/heparin antibodies. There is no significant difference between the study drug groups (p = 0.24). Abbreviation: PF4/H, platelet factor/heparin. Source: From Warkentin et al., 2005b.

thromboprophylaxis after elective hip or knee replacement therapy, similar frequencies of anti-PF4/heparin antibody formation were seen with both anticoagulants (Warkentin et al., 2005b) (Fig. 4). However, anti-PF4/heparin antibodies (whether obtained from fondaparinux-treated patients or from patients with HIT) fail to cross-react in vitro with PF4/fondaparinux, even though they react strongly with PF4/ UFH or PF4/LMWH (see Fig. 2 in Chapter 17). Further, induction of HIT by fondaparinux seems rare, based upon the dearth of such reports to date (Warkentin et al., 2007). Thus, this novel anticoagulant offers the possibility of negligible risk of causing HIT, a concept that can be illustrated using the iceberg model (Fig. 5) (Warkentin, 2006b).

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