Unidad de Farmacología y Terapéutica, Departamento Hospital y Clínicas Veterinarias, Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay.
Grupo de Análisis de Compuestos Traza, Departamento de Química del Litoral, Cenur Litoral Norte, Universidad de la República, EEMAC, Ruta 3 Km 363, 60000, Paysandú, Uruguay.
BMC Vet Res. 2021 Dec 6;17(1):375. doi: 10.1186/s12917-021-03090-7.
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.
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%.
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.
氟虫脲是一种几丁质合成抑制剂，以滴剂形式施用于牛以控制蜱虫。本研究分析了在地方性蜱虫感染下，哺乳期奶牛在滴剂应用模式下氟虫脲在犊牛和奶牛血浆中的水平。在接近分娩时，292 头肉牛按 2.5mg/kg 体重的剂量用商业滴剂氟虫脲处理。共进行了 4 次处理，时间分别为 0 天、32 天、77 天和 117 天。每次给药时，根据滴剂给药模式将奶牛分为长（60cm 滴剂给药表面）和短（30cm 滴剂给药表面）两类。在每个亚组的第三次和第四次给药前（n=10），通过 HPLC-MS/MS 测定奶牛和犊牛血浆中的氟虫脲水平。在整个研究过程中，牛犊对在每个处理日的蜱虫感染情况进行定性检查。两种处理（长和短）方案旨在防止每年蜱虫的持续存在。
在研究的前 117 天内，除了第三次给药（第 77 天）时的三头奶牛和一头小牛外，没有发现有蜱虫存在的动物。在第二次给药后 40 天（第 77 天）（30±5ppb 与 28.5±12ppb，p>0.05）和第三次给药后 45 天（第 117 天）（147±55ppb 与 140±46ppb，p>0.05）之间，两组接受长或短滴剂给药的奶牛之间无差异。与奶牛相比，自由哺乳的犊牛在第二次和第三次给药时的氟虫脲血浆浓度分别增加了（3.3 和 2.9 倍）。然而，两组奶牛和犊牛的血浆氟虫脲浓度在时间上均有显著增加（4.9 倍，p<0.0001 和 2.8 倍，p<0.0001）。在整个试验过程中，两组的蜱虫患病率均为 0%，除了第 77 天为 1%。
本研究的主要结论如下：1）不同的给药模式（长 vs. 短）在氟虫脲的血浆水平上没有差异；2）由于仅对奶牛进行了处理，而哺乳期的犊牛的氟虫脲血浆水平高于奶牛，因此推测药物可能通过乳汁传递，这可能是由于累积效应和持续药物摄入所致。
