Evaluation of inhibitory effects of dipyridamole against bovine and equine piroplasmosis

Dipyridamole, an antiplatelet drug used for the secondary prevention and treatment of stroke, also has antiplasmodial activity and enhances the activity of chloroquine. We evaluated the inhibitory effects of dipyridamole on the growths of Babesia and Theileria parasites. The growth of B. bovis and T. equi was significantly inhibited at a 25 μM concentration of dipyridamole, while B. bigemina and B. caballi were significantly inhibited at 50 μM and 1 μM concentrations of dipyridamole, respectively, on day 3 of cultivation. The half maximal inhibitory concentration (IC50) of dipyridamole was calculated at 39.5±4.5, 26.3±10.9, 13.2±3.6, and 23.5±0.5 μM on the growth of B. bovis, B. bigemina, B. caballi, and T. equi, respectively. In a viability assay, B. bovis, B. bigemina, and T. equi failed to grow at the previous treatment concentration of 100 μM of dipyridamole, while B. caballi had not grown at the previous treatment concentration of 50 μM of dipyridamole. As for in vivo inhibitory assay, treatment with 100 mg/kg of body weight dose of dipyridamole could not inhibit the in vivo growth of B. microti. In conclusion, dipyridamole might be used as a chemotherapeutic agent against bovine and equine piroplasm parasites. However, dipyridamole could not orally treat against B. microti infection