Veterinary Medicine - August 2007 - (Page 534)

Immune-mediated thrombocytopenia O P E E R - R E V I E W E D ciously, and plasma should be considered as an alternative.18 GI protectants may be administered to patients with signs of GI hemorrhage, although the benefit is not proven.19 Drugs that decrease platelet function (e.g. nonsteroidal anti-inflammatory drugs) should be discontinued or avoided.18 Doxycycline (5 to 10 mg/kg orally or intravenously every 12 hours) may be given to treat tick-borne disease, pending the serum antibody titer results.20 If hyphema is present, administer topical 1% prednisolone acetate or 0.1% dexamethasone sodium phosphate three to four times a day with topical 1% atropine two to four times a day.18 Transfusions In some cases, transfusions are needed to address anemia due to hemorrhage. In other instances, transfusions are given in an attempt to increase platelet numbers. Whole blood, platelet-rich plasma, or platelet concentrates are sources of platelets for transfusion. Transfusions with these products transiently boost platelet numbers, but thrombocytopenia rapidly recurs as the circulating life span of donor platelets is markedly reduced in patients with immune-mediated thrombocytopenia, often lasting only a few hours.6,8 the platelet count by about 10,000/µl.8,18 If platelet numbers do not increase or if the increase is not sustained for at least two hours, additional transfusions are not indicated.8 Preparation of platelet-rich plasma and platelet concentrate requires special centrifugation, but these products may be purchased through commercial blood banks.18,21 Although whole blood increases the risk of volume overload and transfusion reaction, it may be given.8 Whole blood transfusion is indicated for patients with severe thrombocytopenic hemorrhage.21 Refrigeration has deleterious effects on platelet viability, so store whole blood at room temperature and use it within four hours of collection.18,21 Immunosuppressive therapy Immunosuppressive therapy is needed to achieve the primary goal in treating immune-mediated thrombocytopenia, which is to restore normal hemostasis. Initially, it is usually adequate to achieve a platelet count > 50,000/µl, as bleeding would no longer be expected. Normalization of platelet numbers may take considerably longer.8 Glucocorticoids. Glucocorticoids are the mainstay of immunosuppres- If the platelet count is adequate to prevent bleeding, you can begin tapering the prednisone dose. Transfusions are also used to stop immediate bleeding in critically ill patients and may be administered before surgery (e.g. splenectomy) or other potentially invasive procedures. Fresh platelet-rich plasma is given at a dose of 10 ml/kg, which is expected to raise sive therapy and have the most immediate effects. They suppress the mononuclear phagocytic system, decrease the affinity of antibody binding to platelets, and are the initial treatment of choice.2,6,8,19 Give prednisone or prednisolone at a dosage of 2 to 4 mg/kg/day orally. Alternatively, dexamethasone may be given at a dose of 0.2 mg/kg intravenously every 24 hours. Platelet numbers usually increase within one week of initial therapy.8 Administer the prednisone until the platelet count normalizes, and then gradually taper it. Evaluate the platelet count before any reduction in the prednisone dose, and do not taper the drug if the platelet count has decreased or has failed to increase. In some cases, normal platelet counts cannot be achieved; however, if the platelet count is adequate to prevent bleeding, tapering can be initiated. Tapering too gradually is associated with increased side effects, and tapering too rapidly may result in relapse of the immune-mediated thrombocytopenia.2 Generally, prednisone is continued at the initial immunosuppressive dose for two to four weeks. If the platelet count is adequate, the dose is reduced by 50% and continued for another two to four weeks. The dose is adjusted in this manner until the lowest effective dose that maintains an adequate platelet count is achieved. A maintenance dose of 0.5 to 1 mg/kg every 48 hours is usually welltolerated if needed. Side effects of prednisone, particularly at high doses, include polyuria, polydipsia, hyperventilation, and other signs of hyperadrenocorticism such as hair loss, muscle wasting, weakness, and predisposition to infection. If the platelet count decreases during the tapering of the prednisone, increase the prednisone to the last dose that effectively maintained normal platelet numbers. If the required dose of prednisone is not acceptable for long-term administration, additional immunosuppressive medications should be added. Vincristine. Vincristine is a vinca alkaloid that transiently increases platelet numbers by stimulating transient megakaryocyte platelet release.8 It may be used to facilitate increasing the 534 August 2007 VETERINARY MEDICINE

Table of Contents Feed for the Digital Edition of Veterinary Medicine - August 2007

Contents A Veterinary Medicine Interview Veterinary Voices Idea Exchange Diagnosis and Treatment of Solar Dermatitis in Dogs Diagnostic Imaging for Linear Foreign Bodies in Cats Overcoming the Diagnostic and Therapeutic Challenges of Canine Immune-Mediated Thrombocytopenia Ophthalmic drugs: What’s new? CE Form Product Preview Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - August 2007

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.