Evaluation of the adulticidal efficacy of imidacloprid 10%/ moxidectin 2.5% spot-on
(Advocate®, Advantage® Multi, Bayer) against Dirofilaria repens in experimentally
infected dogs
This study aimed to evaluate the efficacy of imidacloprid 10%/moxidectin 2.5% spot-on
(Advocate®/Advantage® Multi, Bayer) against adult Dirofilaria (D.) repens in a blinded, placebo
controlled randomised laboratory study. 24 Beagle dogs were experimentally infected with
approximately 75 infective D. repens larvae on study day (SD) 0. A modified Knott test was
used in monthly intervals to monitor the onset of patency and to follow the course of
microfilariaemia after treatment. Treatment was initiated on SD 228 after patency had been
confirmed in 21 dogs. 11 dogs received monthly treatments with imidacloprid/moxidectin at the
minimum therapeutic dose for six consecutive months and 12 control dogs were treated with a
placebo formulation. Approximately one month after the last treatment, all dogs were
euthanized and necropsied for the detection of D. repens worms. 11 control dogs harbored live
adult D. repens (range 2-11, geometric mean 5.44). 8 of 11 imidacloprid/moxidectin treated
dogs were free of live worms. The live worm count was reduced by 96.2% (range 0-1, geometric
mean 0.21). The majority of dead worms was encapsulated and degenerated. After the first
treatment, Knott Tests were negative in all imidacloprid/moxidectin treated dogs and this status
was maintained in 10 dogs until study end. One dog showed a low microfilariae count (1 and
4/ml) on four occasions but was also negative before necropsy. The treatment was well
tolerated in all study animals. It is concluded that six consecutive monthly treatments with
imidacloprid/moxidectin topical solution are effective and safe against adult D. repens and
provide an option for the prevention of further spreading of this zoonotic parasite