Failure of imidocarb dipropionate to clear experimentally induced Ehrlichia canis infection in dogs

The recommended treatment for canine ehrlichiosis is tetracycline or its analog doxycycline, although recent reports have documented ineffective clearing of Erchlichia canis after doxycycline administration. Imidocarb dipropionate is used as an alternative treatment to tetracycline or is used in conjunction with doxycycline. The effectiveness of imidocarb dipropionate in clearing Ehrlichia species from the blood and tissues of dogs with E canis infection has not been thoroughly evaluated. Fifteen dogs were experimentally infected with E canis. Ten dogs were treated with imidocarb dipropionate (6.6 mg/kg, IM, 2 injections given 2 weeks apart). Five infected control dogs were not treated. Blood samples from all 15 dogs were E canis DNA positive by PCR assay by 3 weeks after inoculation (PI), and E canis antibodies were detected by IFA assay by 1 week PI. Blood platelet counts in all dogs were below the reference interval by 4 weeks PI. E canis DNA was detected in bone marrow and splenic aspirates by PCR assay 4 weeks PI but not before infection. Bone marrow aspirates were E canis DNA positive by PCR assay in 14/15 dogs, and splenic aspirates were E canis DNA positive by PCR assay in 13/15 dogs. Blood samples from all treated and control dogs remained positive for E canis DNA by PCR assay, and platelet counts remained below preinoculation values 13 weeks PI (6 weeks after 2nd treatment). As administered in this study, imidocarb dipropionate did not clear experimental E canis infection in dogs.