Therapeutic equivalence of ivermectin 1% and two novel formulations combined of ivermectin 1% + fluazuron 12.5% for the control of in beef cattle from Uruguay.

Background: Novel combinations of ivermectin (IVM) and fluazuron (FLU) are presented as an alternative for the control of ticks in cattle. Applying a combination of drugs with the aim to affect different stages of the parasite's life cycle is established as a potential measure to achieve the control of ticks in cattle.

Aim: To determine the therapeutic equivalence between two novel formulations of IVM 1% combined with FLU 12.5% tested on bovines naturally infested with () .

Methods: Forty adult beef cattle were randomized into four groups ( = 10): IVM [1% (0.2 mg/kg)], combinations groups A and B [IVM 1% (0.2 mg/kg) + FLU 12.5% (2.5 mg/kg), each], and control [untreated]). On days 14, 27, and 49 after administration, 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 the presence of ticks until day 27, on day 14 IVM [odds ratios (OR) 0.013, CI95%: 0.001-0.014, < 0.01], A (OR 0.01, CI95%: 0.00-0.07, < 0.01) and B (OR 0.01, CI95%: 0.00-0.148, < 0.01) groups were different when compared to the control group, unlike on day 27 where only groups A (OR 0.02, CI95%: 0.00-0.17, < 0.01) and B (OR 0.06, CI95%: 0.00-0.46, < 0.01) remained different from the control group. On day 49 post-administration, IVM and B did not differ from the 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%: 0.00-0.13, < 0.01).

Conclusions: Pharmacotechnical differences in combined formulations should be considered in therapeutic equivalence studies.