Even though enrofloxacin is not approved for the treatment
of bovine anaplasmosis in North America, an in
vitro study showed that enrofloxacin inhibited A. marginale
in a dose-dependent manner in erythrocyte culture
(Coetzee et al., 2006b). This was followed by in vivo
experiments where the efficacy of enrofloxacin against
severe experimental A. marginale infections in splenectomized
calves and for clearing persistent A. marginale
infections was evaluated. The results of the in vivo studies
demonstrated the poor efficacy of enrofloxacin for the
treatment of bovine anaplasmosis. Two doses of enrofloxacin
(12.5 mg/kg SC) administered 48 h apart suppressed
but did not eliminate severe A. marginale infections in
splenectomized calves (Coetzee and Apley, 2006). All of
four persistently infected calves treated with enrofloxacin
(5 mg/kg IV q24h for 5 days) before being splenectomized
were designated as treatment failures and had to be
euthanized (Coetzee et al., 2006a).
In addition to the poor efficacy of enrofloxacin for the
treatment of bovine anaplasmosis, Health Canada is recommending
against its use in an extra-label drug use
(ELDU) manner (Health Canada, 2008), and federal USA
law prohibits the ELDU of this drug in food-producing
animals (FDA, 2009).