Evaluation of the therapeutic and preventive efficacy of 2.5 % moxidectin / 10 % imidacloprid (Advocate(®), Bayer animal health) in dogs naturally infected or at risk of natural infection by Dirofilaria repens.

The objective of this GCP-compliant clinical field study was to evaluate the efficacy of the combination of moxidectin (minimum dose of 2.5 mg/kg body weight) and imidacloprid (minimum dose of 10.0 mg/kg body weight) spot-on (Advocate(®)) as a preventive and therapeutic treatment of natural infection by Dirofilaria repens in dogs in the Czech Republic.There were two arms of the study, both negatively controlled. 34 animals were randomly allocated to two groups of the treatment arm; 90 negative animals were randomly allocated to the prevention arm groups. All enrolled dogs were observed physically and blood was sampled monthly for Dirofilaria repens microfilaria counts for 18 months by modified Knott test and PCR. 34 dogs were positive for microfilaria and enrolled in the treatment arm of this study (treated: 18, untreated: 16). The reduction of the log-transformed microfilaria counts was significantly higher in the treatment group on day 28 (p = 0.007), 56, 84 and 112 (p < 0.001). All animals treated were negative after a single treatment. In the untreated control group 93.75 % remained positive (p < 0.001). 87 dogs were negative for microfilaria prior to allocation to the "preventive" arm (treated: 49; untreated: 38; 3 excluded). One dog in the untreated control group became positive for Dirofliaria repens microfilaria, while none of the treated dogs became positive. Advocate(®) was effective in the treatment of dogs infected with microfilaria of Dirofilaria repens. Due to the low rate of natural infections the preventive efficacy could not be proven, but no dog treated became positive.