Plasma disposition and faecal excretion of eprinomectin following topical and subcutaneous administration in non-lactating dairy cattle

Season-Long Simplification of Insect Communities in Dung From Cattle Treated With an Extended-Release Formulation of the Parasiticide Eprinomectin

Cattle treated with LongRange®, an injectable formulation of the parasiticide eprinomectin, fecally excrete insecticidal residues for an extended period post application. We examined the nontarget effect of these residues by comparing insect communities developing in dung of untreated cattle (week 0) with those developing in dung of cattle treated 1, 2, 4, 8, 12, 16, 20, and 24 or 25 weeks previously. Chemical analyses of dung showed that eprinomectin concentrations peaked at 1 week post application and were still detectable at 25 weeks. Results from two separate experiments showed that dung of untreated cattle supported more total insects (beetles, flies, parasitoid wasps) and insect species than did dung of cattle treated for ≤12 weeks (Experiment 1) and ≤25 weeks (Experiment 2) previously. For the two experiments, an effect of residue on individual taxa was either not detected (nine cases) or was determined to suppress insect development in dung of cattle treated for 8-12 weeks (two cases), 12-16 weeks (three cases), 16-20 weeks (two cases), or 24 or 25 weeks (six cases) previously. Flies and their parasitoid wasps were particularly sensitive to residues with suppression often at or near 100%. These results show that cattle treated with LongRange in spring will fecally excrete residues for the entire grazing season with an associated simplification of the dung insect community. The effect of this simplification on the long-term health on dung-breeding populations of insects on pastures and dung degradation was not examined in the present study, but merits future research. Environ Toxicol Chem 2023;42:684-697. © 2023 His Majesty the King in Right of Canada. Environmental Toxicology and Chemistry © 2023 SETAC. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Preparation of Eprinomectin Nanoemulsions and Determination of Their Pharmacokinetics and Pharmacodynamics in Dairy Cows

This study aimed to develop an anthelmintic that leaves no residues and is safe and efficient for use in cows. We constructed classical pseudoternary phase diagrams using experimental animal data to optimize and characterize the eprinomectin nanoemulsion formulas. The emulsion samples prepared with ethyl acetate, polysorbate 80, and 1-propanediol as the main components were transparent and uniform when observed under a Hitachi transmission electron microscope (TEM) system. A Mastersizer 3000 laser particle size analyzer was used to determine the particle sizes of the prepared nanoemulsions. The nanoemulsions were homogeneously dispersed, with an average particle size of 12.61 nm and a polydispersity index of (PDI) 0.297. High-performance liquid chromatography confirmed no statistically significant changes in the samples after 24 months at 4 °C, 25 °C, and 37 °C; the samples exhibited long-term stability. The PK/PD studies confirmed that the injection of eprinomectin nanoemulsions at a dose of 0.2 mg/kg body weight was effective, with a withdrawal period of 0 days for dairy cows. The total extermination rate of the nanoemulsions against adult nematodes was 98.40±1.52%. The AUC_milk/plasma ratio was 0.67±0.03. The optimal dose was found to be 0.2 mg/kg body weight.

Pharmacokinetics and milk excretion pattern of eprinomectin at different dose rates in dairy cattle

This study aimed at determining the plasma disposition kinetics of eprinomectin (EPM) and EPM excretion pattern through milk after topical administration to dairy cattle at the recommended dose of 0.5 mg/kg and at 1 and 1.5 mg/kg. A high variability in the plasma concentration profiles was observed among animals, particularly in the Cmax values, with a coefficient of variation between 39 and 53%. The Cmax and AUC values were significantly affected by the dose administered at 1.5 mg/kg. However, such differences did not seem to follow a linear pattern among treatments. These parameters did not differ among dose rates after dose normalization; nevertheless, the simulation of a linear kinetic disposition showed a mean plasma AUC value of 254 ng.d/ml instead of the observed value of 165 ng.d/ml. EPM concentration profiles in milk were significantly lower than those measured in plasma. The Cmax and AUC milk-to-plasma ratios ranged from 0.14 to 0.26 and 0.16 to 0.21, respectively (p>0.05). The low milk-to-plasma ratio of EPM accounted for a low percentage of the fraction of the administered dose excreted through milk, being significantly higher at a dose rate of 0.5 mg/kg (0.07%) of EPM than at 1.5 mg/kg (0.04%) (p<0.05). The topical administration of EPM to lactating dairy cows at higher doses than that recommended for gastrointestinal nematodes showed a milk excretion pattern with a zero milk withdrawal period. In conclusion, the administration of topical EPM formulation at 1 or 1.5 mg/kg may be a valuable tool to be used in regional strategic deworming programs aimed to control ectoparasite infections in dairy production systems.

Injectable eprinomectin for cattle: Tick efficacy and pharmacokinetics

The aims of the present study were to evaluate the pharmacokinetic profile and efficacy of eprinomectin (EPM) against Rhipicephalus microplus in cattle of a new injectable form of EPM (Voss Performa®). The product was administered subcutaneously at a dose of 200 μg EPM/kg, in a single dose. The efficacy of EPM against R. microplus in cattle was evaluated through field and stall tests. Studies were performed to estimate the pharmacokinetic parameters of EPM with the purpose of better understanding the kinetics of the formulation. The formulation was effective in controlling R. microplus in both naturally and artificially infested cattle, providing efficacy greater than 95%. The results of pharmacokinetic study were C_max of 47.15 ± 22.20 ng/ml, T_max of 1.33 ± 0.492 days, T_1/2 of 2.96 ± 1.212 days, AUC_0-t of 228.08 ± 57.30 ng day ml^-1 , and AUC_0-∞ of 240.50 ± 58.44 ng day ml^-1 . Therefore, the new injectable EPM formulation becomes an important alternative for the control of cattle tick in Brazil.

Review of the Eprinomectin effective doses required for dairy goats: Where do we go from here?

Eprinomectin (EPM) has been recently granted a marketing authorisation in the European Union for use in goats, with a zero-day milk withdrawal period. Considering the high prevalence of benzimidazole resistance worldwide and the economic implications of managing milk residues, EPM may today be considered the main (or even the only) affordable treatment option, at least in dairy goats in the EU. However, the chosen dose (1 mg/kg) seems to be suboptimal, especially for lactating goats, and the chosen route of administration (Pour-on) highly subject to inter-individual variability. Considering the scarcity of anthelmintic resources, such a dosage regimen might threat the sustainability of this crucial drug in goat milk production and needs to be urgently discussed and reassessed.

Eprinomectin antiparasitic affects survival, reproduction and behavior of Folsomia candida biomarker, and its toxicity depends on the type of soil

The objective of this study was to evaluate the toxicity of the antiparasitic agent eprinomectin in two subtropical soils, using ecotoxicological lethality, reproduction and avoidance behavior tests with springtails (Folsomia candida). Eprinomectin concentrations were 0 (control), 0.5, 1, 2, 4, 8, 12, 16 and 20 mg kg^-1 of dry soil combined with either Entisol or Oxisol soils. Statistically significant toxic effects of eprinomectin on springtails were observed in both soils. Eprinomectin was lethal starting at 8 mg kg^-1 of dry soil in Entisol, and 20 mg kg^-1 of dry soil in Oxisol, with effects less than 50% at lethal concentrations. Reductions in the reproduction rate of the springtails were also observed starting at 8 mg kg^-1 of dry soil in Entisol, and 0.5 mg kg^-1 of dry soil in Oxisol. EC_repr50 value calculated for Entisol was 4.38 ± 0.62 mg kg^-1 of dry soil; for Oxisol the EC_repr50 was above the highest tested concentration. For avoidance behavior, the effect occurred from 0.5 mg kg^-1 of dry soil for both soils. In Entisol, all concentrations caused avoidance of more than 95%, and in Oxisol the EC_avoi50 value was 1.33 ± 0.83 mg kg^-1 of dry soil. We conclude that eprinomectin affected survival, reproduction and caused avoidance behavior of F. candida in both soils. The toxic effects were greater as the concentration in the soils increased. The effects in Oxisol were less intense than those in Entisol with respect to the affected springtails. This discrepancy may be attributed to the different physicochemical characteristics of the soils that determine the retention capacity for eprinomectin; in particular, there are greater contents of clay, organic matter and cation exchange capacity in Oxisol.

Eprinomectin from a sustained release formulation adversely affected dung breeding insects

The insecticidal activity of parasiticide residues in dung of cattle treated with a sustained release eprinomectin formulation was examined, and an improved eprinomectin dung residue extraction method is presented. Emergent insect abundance and richness were significantly reduced in all post-treatment intervals (7, 14, 28, 56, 84, 112, and 140 d), relative to pre-treatment. Emergent insect diversity was reduced for between 84 and 112 d post-treatment. Collembola were not affected by residues. Chemical analyses subsequently documented residues of eprinomectin in dung of each collection period post-treatment at levels expected based on previously reported excretion profiles for this product. Cattle subcutaneously injected with this product excreted residues that reduced dung-breeding insect emergence for 5 mo post-treatment. The consequences of these long-term non-target effects to pasture ecosystems are not known.