Background: Fluazuron is a chitin synthesis inhibitor administered as a pour-on formulation in cattle for tick control. This study analyzes under endemic tick infestation, the incidence of the pour-on application pattern on the plasma levels of fluazuron in cows and calves in the lactation period of the beef cow. Three hundred and thirteen beef cows around parturition were treated with commercial pour-on formulation of fluazuron at a rate of 2.5 mg/kg of body weight. A total of 4 treatments were carried out with a dosing period set in a range of 32 to 45 days. At each administration time, the cows were grouped according to the pour-on administration pattern: long (~60 cm pour-on application surface) and short (~30 cm pour-on application surface). Fluazuron levels in cattle and calves plasma were determined before the third and fourth application for each subgroup (n=10) by HPLC-MS/MS. During the entire study cow–calf pairs were maintained under field conditions and qualitatively examined for tick infestation on the day of each treatment. Both treatment (long and short) schemes were designed to prevent the annual persistence of ticks.Results: None of the groups presented ticks during the first 117 days of the study. There were no differences after 40 days post-treatment of the second application (30±5 ppb vs 28.5±12 ppb, P>0.05) and 45 days after the third application (147±55 ppb vs 140±46 ppb, P >0.05) between groups of cows treated with the long or short pour-on application, respectively. Plasma concentration of fluazuron at second and third application was increased (3.3 and 2.9 times, respectively) in calves under free suckling compared to cows. Nevertheless, both groups of cows (4.9 times) and calves (2.8 times) showed a significant increase in plasma concentration of fluazuron between times (P<0.05). In both groups, tick prevalence was 0% throughout the trial, except for day 77, which reached 1%.Conclusions: The main conclusions of this study were the following: 1) Different administration patterns (long vs short) did not differ in plasma levels of fluazuron.; 2) Given that only the cattle were treated, and lactating calves presented higher plasma levels of fluazuron than cows, passage through milk appears to be relevant and possibly due to a cumulative effect and continuos drug intake.

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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 Rhipicephalus (Boophilus) microplus. Methods: Forty adult beef cattle were randomized into four groups (n = 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, p < 0.01], A (OR 0.01, CI95%: 0.00–0.07, p < 0.01) and B (OR 0.01, CI95%: 0.00–0.148, p < 0.01) groups were different when compared to the control group, unlike on day 27 where only groups A (OR 0.02, CI95%: 0.00–0.17, p < 0.01) and B (OR 0.06, CI95%: 0.00–0.46, p < 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, p < 0.01). Conclusions: Pharmacotechnical differences in combined formulations should be considered in therapeutic equivalence studies.

Background Fluazuron is a chitin synthesis inhibitor administered as a pour-on formulation in cattle for tick control. This study analyzes under endemic tick infestation, the incidence of the pour-on application pattern on the plasma levels of fluazuron in calves and cows in the lactation period of the beef cow. Two hundred and ninety-two beef cows around parturition were treated with a commercial pour-on formulation of fluazuron at a rate of 2.5 mg/kg of body weight. A total of 4 treatments were carried out on days 0, 32, 77, and 117. At each administration time, the cows were grouped according to the pour-on administration pattern: long (~ 60 cm pour-on application surface) and short (~ 30 cm pour-on application surface). Fluazuron levels in cows and calves plasma were determined before the third and fourth application for each subgroup (n = 10) by HPLC-MS/MS. During the entire study, cow-calf pairs were maintained under field conditions and qualitatively examined for tick infestation on the day of each treatment. Both treatments (long and short) schemes were designed to prevent the annual persistence of ticks. Results No animals with presence of ticks were identified during the first 117 days of the study, except for three cows and one calf at the time of the third application (day 77). There were no differences after 40 days (day 77) post-treatment of the second application (30 ± 5 ppb vs. 28.5 ± 12 ppb, p > 0.05) and 45 days (day 117) after the third application (147 ± 55 ppb vs 140 ± 46 ppb, p > 0.05) between groups of cows treated with the long or short pour-on application, respectively. Plasma concentration of fluazuron at second and third application was increased (3.3 and 2.9 times, respectively) in calves under free suckling compared to cows. Nevertheless, both groups of cows and calves showed a significant increase in plasma concentration of fluazuron between times (4.9 times, p < 0.0001 and 2.8 times, p < 0.0001, respectively). In both groups, tick prevalence was 0% throughout the trial, except for day 77, which reached 1%. Conclusions The main conclusions of this study were the following: 1) Different administration patterns (long vs. short) did not differ in plasma levels of fluazuron.; 2) Given that only the cows were treated and lactating calves presented higher plasma levels of fluazuron than cows, passage through milk appears to be relevant and possibly due to a cumulative effect and continuous drug intake.