Luis Alvarez

Background/Objectives: Combination of antiparasitic drugs with different mechanisms of action has been suggested as an effective strategy to delay the development of parasite resistance. Considering the need to understand the pharmacological basis of drug combinations, the current study evaluated the potential pharmacokinetic (PK) interactions and the clinical efficacy (pharmacodynamic response) occurring after the subcutaneous administration of ivermectin (IVM) and levamisole (LEV), administered either as single treatments or concurrently to different groups of parasitized calves on three commercial farms (A, B and C). Methods: Forty-five (45) male calves naturally infected with gastrointestinal nematodes were randomly allocated into three groups (n = 15): IVM, treated with IVM by subcutaneous injection (0.2 mg/kg); LEV, treated subcutaneously with LEV (8 mg/kg); IVM + LEV, simultaneously treated with IVM and LEV (two subcutaneous injections at the same dose rates). Seven animals from each treated group (farm C) were randomly selected to perform the PK study. Drug concentrations were measured by HPLC. The therapeutic response (efficacy) was determined at 14 days after treatment by the fecal egg reduction test. Results: The mean area under the concentration vs time curve (AUC) for IVM obtained after administration of IVM alone (274 ± 65.1 ng.d/mL) was similar to that obtained when IVM was co-administered with LEV (295 ± 111 ng.d/mL). Likewise, mean LEV AUC values were similar after LEV administration alone (8.90 ± 2.69 µg.h/mL) or combined with IVM (9.11 ± 1.82 µg.h/mL). No adverse PK interactions were observed after the combined treatment, with similar PK parameters (p > 0.05) obtained between the single-drug and the combination-based strategies. On farm A, the overall fecal egg reductions were 38% (IVM), 99% (LEV) and 100% (IVM + LEV). While Cooperia spp. and Haemonchus spp. showed reduced susceptibility to IVM treatment, LEV demonstrated high efficacy against both genera, with only a minimal proportion of Haemonchus spp. remaining after treatment. Similarly, total fecal egg reductions were 42% (IVM), 99% (LEV) and 100% (IVM + LEV) on farm B, and 54% (IVM), 99% (LEV) and 100% (IVM + LEV) on farm C. On those farms, IVM was ineffective against Cooperia spp. and/or Haemonchus spp., while LEV failed to control Ostertagia spp. Remarkably, the combination of both molecules was the only treatment that achieved 100% efficacy against all nematode genera (Cooperia, Ostertagia, Haemonchus and Oesophagostomum spp.). Conclusions: Based on the described PK and pharmacodynamic (PD) assessments, the IVM + LEV combination appears to be a promising pharmacological option for controlling resistant gastrointestinal nematodes in cattle, with the additional potential to delay the progression of nematode anthelmintic resistance. Overall, the study provides original and robust pharmacokinetic and efficacy data that contribute to the optimization of parasite control strategies in cattle. This drug combination strategy may enhance treatment efficacy and contribute to improved parasite control in cattle production systems.

Combination of antiparasitic drugs with different mechanisms of action has been suggested as an effective strategy to delay the development of parasite resistance. Upon the need to understand the pharmacological basis of drug combinations, the current study evaluated the potential pharmacokinetic (PK) interactions and the clinical efficacy (pharmacodynamic response) occurring after the subcutaneous administration of ivermectin (IVM) and levamisole (LEV) given both separately and co-administered to parasitized calves on three commercial farms (A, B and C). Sixty (60) male calves naturally infected with gastrointestinal nematodes were randomly allocated into three groups (n= 15): IVM: treated with IVM by subcutaneous injection (0.2 mg/kg); LEV: treated subcutaneously with LEV (8 mg/kg); IVM+LEV: simultaneously treated with IVM and LEV (2 subcutaneous injections at the same dose rates). Seven (7) animals from each treated group (farm C) were randomly selected to perform the PK study. Drug concentrations were measured by HPLC. The therapeutic response (efficacy) was determined at 14 days after treatment by the fecal eggs reduction test (FECRT). The mean IVM area under the concentration vs time curve (AUC) obtained after administration of IVM alone (274 ng.d/mL) was similar to that obtained when IVM was co-administered with LEV (295 ng.d/mL). Likewise, mean LEV AUC values were similar after LEV administration alone (8.90 µg.h/mL) or combined with IVM (9.11 µg.h/mL). No adverse PK interactions were observed after the combined treatment, with similar PK parameters (P>0.05) obtained between the single-drug and the combination-based strategies. On farm A, the overall therapeutic responses (clinical efficacy) were 38% (IVM), 99% (LEV) and 100% (IVM+LEV). While the gastrointestinal nematode species Cooperia spp. and Haemonchus spp. survived the IVM treatment, Haemonchus spp. survived the LEV treatment. Similarly, total efficacies were 42% (IVM), 99% (LEV) and 100% (IVM+LEV) on farm B, and 54% (IVM), 99% (LEV) and 100% (IVM+LEV) on farm C. On those farms, IVM was ineffective against Cooperia spp. and/or Haemonchus spp., while LEV failed to control Ostertagia spp. Remarkably, the combination of both molecules was the only treatment that achieved 100% efficacy against all nematode genera (Cooperia, Ostertagia, Haemonchus and Oesophagostomum spp.). Based on the described PK-pharmacodynamic (PK-PD) assessment, the IVM+LEV combination appears to be a promising pharmacological option for controlling resistant gastrointestinal nematodes in cattle, with the additional potential to delay the progression of nematode anthelmintic resistance. Overall, the work described here contributes with sound and original pharmacology data useful to optimize parasite control in livestock. This drug combination strategy may enhance treatment efficacy while promoting more sustainable parasite management practices in cattle production systems.

Albendazole (ABZ) is a methylcarbamate benzimidazole anthelmintic used to control gastrointestinal parasites in several animal species and humans. The type of diet has been identified as a major determinant for ABZ pharmacokinetics in different animal species and humans. The work described here assesses the pattern of the absorption and the systemic availability of ABZ and its metabolites after its oral administration to pigs under different feed management plans. Eighteen pigs (5 months old, local ecotype breeds) were distributed into three experimental groups. In the fasting group, the animals fasted for 8 h prior to treatment. In the pellet + oil and pellet groups, the animals were fed ad libitum with a commercial pelleted-based diet with or without the addition of soya oil. An ABZ suspension was orally administered at 10 mg/kg. Blood samples were taken over the 48 h post-treatment. The plasma samples were analyzed by HPLC. Under the described experimental conditions, the ingestion of the pellet-based diet with or without the soya oil before ABZ treatment did not significantly (p < 0.05) modify the plasma disposition kinetics of the ABZ sulfoxide (ABZSO, the main ABZ metabolite) compared to that observed in the fasting pigs. Both ABZ metabolites (ABZSO and ABZ sulphone) reached similar peak concentrations and systemic exposures in all the experimental groups regardless of the feeding management. However, the addition of oil to the pelleted food enhanced the pattern of ABZ absorption, which was reflected in the higher (p < 0.05) concentration profiles of the active ABZSO metabolite measured between 12 and 48 h post-treatment compared to the pigs fed with the pelleted food alone. Although this effect may not be therapeutically relevant after ABZ administration as a single oral dose, the overall impact of the type and feeding conditions when ABZ is supplemented with food for several days should be cautiously evaluated.

The egg development test is a useful in vitro tool to detect albendazole (ABZ) resistance in Fasciola hepatica. ABZ is the only flukicidal compound with ovicidal activity. The described test is based on the ABZ capacity to affect parasite egg development and hatching in susceptible parasites, while this effect is lost in ABZ-resistant liver fluke isolates. Among many advantages, it is noted that the diagnostic test can be performed on eggs isolated from fecal samples (sheep and cattle), avoiding the sacrifice of animals necessary in controlled efficacy trials. The egg development test described here is a simple, inexpensive, and accessible method, previously employed for diagnosis of ABZ resistance in F. hepatica.

AIMS: To assess the comparative drug systemic exposure of a reference (RF) and four test (Test I, Test II, Test III and Test IV) formulations of triclabendazole (TCBZ) in heifers. METHODS: Thirty Holstein heifers were randomly distributed into five groups (n=6 per group). Animals in the RF group received the reference formulation (Fasinex), and those in the other groups received different commercially available TCBZ formulations (Test I, Test II, Test III and Test IV). All treatments were orally administered at 12 mg/kg bodyweight. The concentrations of TCBZ metabolites in plasma between 0 and 168 hours after treatment were quantified by high-performance liquid chromatography (HPLC). RESULTS: Triclabendazole sulphoxide (TCBZ. SO) and TCBZ-sulphone (TCBZ.SO2) were the only analytes recovered in plasma. Only the Test I formulation did not differ from the RF for all pharmacokinetic parameters measured for either metabolite (p>0.8). The TCBZ. SO area under the concentration vs. time curve for Test II formulation (268.9 mu g.h/mL) was lower, and for Test III (619.9 mu g.h/mL) and Test IV (683.4 mu g.h/mL) was higher, than the RF (418.1 mu g.h/mL) (p<0.005). CONCLUSION: Based on the currently available bioequivalence criteria, the only test formulation under evaluation that could be considered equivalent to the RF was the Test I formulation, which demonstrated an equivalent systemic exposure for the active TCBZ. SO metabolite. This comparison of TCBZ pioneer and test formulations in cattle raises awareness of the need for further quality control for drug approval in the veterinary pharmaceutical field in many regions of the world.