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Abbreviations: DDAVP, desmopressin; EACA, amicar; factor VIII: vWF concentrates; see Table 11-14.

Abbreviations: DDAVP, desmopressin; EACA, amicar; factor VIII: vWF concentrates; see Table 11-14.

of patients with type 3 disease who have received multiple transfusions. Administration of FVIII concentrates containing vWF to these patients is contraindi-cated because life-threatening anaphylactic reactions may result. In this setting, administration of recombinant FVIII, which is devoid of vWF, can raise FVIII levels to hemostatic levels. In the absence of vWF the half-life of the infused FVIII will be short (1-2 hours) and administration of high doses, at short intervals or by continuous infusion, will be required. Administration of rFVIIa at a dose of 90 ^g/kg every 2 hours has produced hemostasis for some of these patients.

Platelet-Type Pseudo-von Willebrand Disease

Platelet-type pseudo-vWD is due to a gain of function mutation defect in the platelet GP Ib receptor. This platelet disorder has a phenotype similar to type 2B vWD. Excessive binding of vWF to platelet GP Ib receptor causes platelet activation and vWF removal from the circulation, plasma concentrations of vWF are reduced, and platelet aggregation is increased. Bleeding in this disorder should be treated with platelet transfusions.

Acquired von Willebrand Disease

Acquired vWD may present as a marked reduction in levels of von Willebrand antigen in a person who does not have a lifelong bleeding disorder. The onset has been associated with a variety of conditions including Wilms' tumor, other neoplasms, autoimmune diseases (e.g., SLE), myeloproliferative disease, lymphoproliferative disorders, use of various drugs, as well as in individuals with angiodysplastic lesions. Proposed mechanisms include specific autoantibodies, adsorption onto malignant cell clones, and depletion in conditions of high vascular shear force. Therapeutic interventions are directed at controlling acute bleeding episodes, treating the underlying disorder in the hope of correcting the abnormalities of vWF, and effecting antibody elimination. DDAVP infusion is the initial treatment of choice for achieving hemostasis; plasma-derived FVIII/vWF concentrates are the second choice. In either case clearance of the von Willebrand factor will be accelerated and levels must be monitored. IVIG, plasmapheresis, and/or immunosuppressive drugs may be useful for eliminating antibody.

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