Abstract
Background: Novel combinations of ivermectin and fluazuron are presented as an alternative for cattle tick control. Applying combination of drugs with the aim to affect different stages of the parasite´s life cycle is stablished as a potential measure to achieve control of cattle tick.
Aim: To determine therapeutic equivalence between two novel formulations of ivermectin 1% combined with fluazuron 12.5 % tested on bovines naturally infested with Rhipicephalus (Boophilus) microplus.
Methods: Forty adult beef cattle were randomized into four groups (n = 10): IVM [ivermectin 1% (0.2 mg/kg)] and combinations groups A and B [ivermectin 1% (0.2 mg/kg) + fluazuron 12.5% (2.5 mg/kg), each] and Control [untreated]). During 49 days the presence of ticks was ranked as null, low, medium and high; a cumulative link model was adjusted to evaluate treatment response. Results: Although all groups had some animals with presence of ticks until day 27, on day 14 IVM (OR 0.013, CI95%: 0.001 to 0.014, p<0.01), A (OR 0.01, CI95%: 0.00 to 0.07, p < 0.01) and B (OR 0.01, CI95%: 0.00 to 0.148, p < 0.01) groups were different when compared to the Control group, unlike on day 27 where only groups A (OR 0.02, CI95%: 0.00 to 0.17, p<0.01) and B (OR 0.06, CI95%: 0.00 to 0.46, p<0.01) remained different from the Control group. On day 49 post-administration IVM and B did not differ from Control group, with 0.95 probability (CI95% 0.92-1.02) of high parasite burden. At day 49 post-administration, Group A was the only group free of ticks (OR 0.01, CI95%: 0.00 to 0.13, p<0.01).
Conclusions: Pharmacotechnical differences in combined formulations should be considered in therapeutic equivalence studies.

Key words: Bovine, Drug combination, Ectoparasites, Tick