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Pathophysiological mechanisms of immune-mediated thrombocytopenia (ITP) in humans and dogs are similar. Romiplostim has thrombopoietic eﬀects due to the agonism at the thrombopoietin receptor (TPO-R). Romiplostim is utilized in humans for treatment of refractory ITP, however it has not been used in dogs thus far. Because of the similarity of ITP in humans and dogs it should be evaluated whether romiplostim can be used as a new therapeutic option in dogs with ITP that cannot be controlled by standard therapy. From 10/2014 until 12/2015 7 dogs with refractory or recurring ITP were treated with romiplostim. Inclusion criteria were a diagnosis of primary or secondary ITP based on complete medical records, platelet counts < 150,000/ll and a positive platelet-bound antibody test. Primary ITP was only diagnosed, if there was no evidence of any cause, which might have triggered platelets’
destruction. Discrimination of primary and secondary forms of ITP was based on a complete diagnostic work-up (complete blood count, blood smear evaluation, testing for erythrocyte agglutination, clinical chemistry, coagulation panel, diagnostic imaging, tests for infectious diseases, and immunological testing). Primary and secondary ITP was diagnosed in 5 (2 of them Evans’ syndrome) and 2 dogs (with Ehrlicha canis infection), respectively. All dogs were pretreated with prednisolone, mycophenolate mofetil, cyclosporine, and dexamethasone alone or in combination. Due to inadequate response or relapses, romiplostim was administered in addition (3–5 lg/kg, median (m) 4.7 lg/kg) subcutaneously. In 5 of 7 dogs, an increase in platelet counts was noted 3–6 days after the ﬁrst romiplostim injection. One dog with primary ITP had an increase after 10 days and the second administration (10 lg/kg). Another dog with secondary ITP did not respond to 5 but to 13 lg/kg. This dog was lost to follow-up. One dog with a platelet count in the reference range was euthanized
due to immune-mediated hemolytic anemia after 2.5 months. During the observation period (3–53 weeks, median 10.7) in 6 of 7 dogs the initially given dose could be reduced. None of the treated dogs developed any side eﬀects. Concomitant therapy with other drugs was gradually reduced and halted in 4 of the dogs when the platelet count was stable. Interestingly, none of the 6 dogs relapsed during the observation period. The results of this pilot study suggest that the human drug romiplostim may represent a novel therapeutic option in dogs with refractory ITP.