Reply:

We thank Dr. Blom for his interest in our article and pertinent comments. We should, however, clarify that the etiology of thrombus at the time of aneurysm coil treatment depends on not only endothelial platelet interactions mediated through GP Ib/IX, but also platelet-platelet interaction resulting from subsequent platelet activation and a conformational change in the GP IIb/IIIa site.1 Altered intravascular and intra-aneurysmal hemodynamics, presence of foreign material, and possibly electrothrombosis contribute further to platelet interaction and thrombosis. In these circumstances the acute clot formed is platelet rich and highly susceptible to the GP IIb/IIIa inhibitors. We demonstrated the reappearance of an aneurysm neck in case 2 after abciximab administration, which we interpreted as facilitated platelet dysaggregation in a freshly thrombosed portion of the aneurysm.

Dr. Blom correctly highlights the difference in binding characteristics between abciximab and eptifibatide. Clearly, their use is predicated by several clinical factors. A higher affinity binding agent (abciximab) is desirable for prevention of platelet aggregation, but in the context of platelet disaggregation a low-affinity compound (eptifibatide) is able to dissociate a greater number of platelets in a given time.2 Despite a longer plasma half-life, the competitively binding, smaller-molecular-weight inhibitors have a shorter receptor blockade and therefore require greater and longer infusions to maintain adequate blockage.3 As a result, emergent and elective surgery may be performed immediately or following a 2–4-hour duration for eptifibatide and 12-hour or 1–2-day delay for abciximab. The smaller-size compounds may allow superior penetration through fibrin-fibrinogen networks, potentially contributing to superior potency2 and both short-acting inhibitors are less expensive than abciximab.4

Thrombocytopenia occurs more frequently in patients with abciximab (1%–5%) than the other inhibitors.5 Furthermore, antibody production against abciximab is described as raising theoretical concerns for autoimmune response following exposure, though repeat administration appears to be safe6

In clinical practice (in the absence of renal failure), these differences do not seem to affect drug preference, and the GP IIb/IIIa inhibitors remain an effective treatment of intraprocedural thrombotic complications.