Comparative drug systemic exposure and clinical efficacy against resistant nematodes in lambs treated with different albendazole formulations

Therapeutic advantages of the combined use of closantel and moxidectin in lambs parasitized with resistant gastrointestinal nematodes

The serious widespread development of nematode resistance has motivated the use of combined anthelmintic formulations. However, the advantages/disadvantages of the combined use of anthelmintics require further scientific characterization. The goals of the current trial were a) to characterize the pharmacokinetics of closantel (CLO) and moxidectin (MXD) administered both subcutaneously (sc) and orally either separately or co-administered (CLO + MXD) to lambs; b) to compare the nematodicidal activity of both molecules given individually or co-administered to lambs infected with resistant nematodes. Seventy (70) Corriedale lambs naturally infected with multiple resistant gastrointestinal nematodes were involved in the pharmacokinetic and efficacy trials. The animals were allocated into six groups (n = 10) and treated with either CLO, MXD, or with the CLO + MXD combined formulation by both the oral and sc routes. Additionally, an untreated control group (n = 10) was included for the efficacy trial. The efficacy was estimated by the faecal egg count reduction test (FECRT). Higher systemic exposure of both CLO and MXD was observed after the sc compared to the oral administration in lambs. The combined administration of CLO + MXD did not markedly alter their disposition kinetics. At 13 days post-treatment, the administration of both molecules as a single active principle reached efficacy levels ranging between 80% (MXDoral), 84% (CLOoral), 85% (CLOsc), and 92% (MXDsc). The combined oral and sc treatments reached 99% efficacy. No adverse effects were observed after the combined treatment of CLO + MXD, and their co-administration did not show any adverse pharmacokinetic interaction. The combined effect of CLO + MXD successfully restored the maximum efficacy levels, which were not reached by the individual active ingredients.

Confounding factors affecting faecal egg count reduction as a measure of anthelmintic efficacy

Increasing anthelmintic resistance (AR) in livestock has stimulated growing efforts to monitor anthelmintic effectiveness (AE) on livestock farms. On-farm assessment of AE relies on measuring the reduction in faecal egg count (FEC) following treatment; and if conducted rigorously, qualifies as a formal FEC reduction test (FECRT) for AR. Substantial research effort has been devoted to designing robust protocols for the FECRT and its statistical interpretation; however, a wide range of factors other than AR can affect FEC reduction on farms. These are not always possible to control, and can affect the outcome and repeatability of AE measurements and confound the on-farm classification of AR using FECRT. This review considers confounders of FEC reduction, focusing on gastrointestinal nematodes of ruminants, including host and parasite physiology and demography; pharmacokinetic variation between drugs, parasites and hosts; and technical performance. Drug formulation and delivery, host condition and diet, and seasonal variation in parasite species composition, can all affect AE and hence observed FEC reduction. Causes of variation in FEC reduction should be attenuated, but this is not always possible. Regular monitoring of AE can indicate a need to improve anthelmintic administration practices, and detect AR early in its progression. Careful interpretation of FEC reduction, however, taking into account possible confounders, is essential before attributing reduced FEC reduction to AR. Understanding of confounders of FEC reduction will complement advances in FECRT design and interpretation to provide measures of anthelmintic efficacy that are both rigorous and accessible.

Current Challenges for Fasciolicide Treatment in Ruminant Livestock

Pharmacological treatment remains essential to control fasciolosis in areas where infection is endemic. However, there are major constraints to treating food-producing animals. Of particular concern is the lack of flukicides for treating early Fasciola infections in ruminant livestock in some countries. In addition, the information provided in package leaflets, particularly regarding withdrawal periods, is often incomplete, confusing, and/or contradictory. International regulatory bodies should harmonize the use of flukicides in livestock in favor of fairer, safer international trade. In addition, monitoring the efficacy of fasciolicides on farms is also essential to minimize the spread of drug-resistant populations of Fasciola. The current situation regarding flukicide formulations in the European Union and other, non-European countries is analyzed in this review paper.

Pharmacokinetic comparison of different flubendazole formulations in pigs: A further contribution to its development as a macrofilaricide molecule

Despite the well established ivermectin activity against microfilaria, the success of human filariasis control programmes requires the use of a macrofilaricide compound. Different in vivo trials suggest that flubendazole (FLBZ), an anthelmintic benzimidazole compound, is a highly efficacious and potent macrofilaricide. However, since serious injection site reactions were reported in humans after the subcutaneous FLBZ administration, the search for alternative pharmaceutical strategies to improve the systemic availability of FLBZ has acquired special relevance both in human and veterinary medicine. The goal of the current experimental work was to compare the pharmacokinetic plasma behavior of FLBZ, and its metabolites, formulated as either an aqueous hydroxypropyl- β -cyclodextrin-solution (HPBCD), an aqueous carboxymethyl cellulose-suspension (CMC) or a Tween 80-based formulation, in pigs. Animals were allocated into three groups and treated (2 mg/kg) with FLBZ formulated as either a HPBCD-solution (oral), CMC-suspension (oral) or Tween 80-based formulation (subcutaneous). Only trace amounts of FLBZ parent drug and its reduced metabolite were measured after administration of the different FLBZ formulations in pigs. The hydrolyzed FLBZ (H-FLBZ) metabolite was the main analyte recovered in the bloodstream in pigs treated with the three experimental FLBZ formulations. The oral administration of the HPBCD-solution accounted for significantly higher (P < 0.05) Cmax and AUC (23.1 ± 4.4 μg h/mL) values for the main metabolite (H-FLBZ), compared with those observed for the oral CMC-suspension (AUC = 3.5 ± 1.0 μg h/mL) and injectable Tween 80-based formulation (AUC: 7.5 ± 1.7 μg h/mL). The oral administration of the HPBCD-solution significantly improved the poor absorption pattern (indirectly assessed as the H-FLBZ plasma concentrations) observed after the oral administration of the FLBZ-CMC suspension or the subcutaneous injection of the Tween 80 FLBZ formulation to pigs. Overall, the work reported here indicates that FLBZ pharmacokinetic behavior can be markedly changed by the pharmaceutical formulation.

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The pharmacokinetics of three different FLBZ formulations was assessed in pigs.

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Hydrolyzed-FLBZ was the main metabolite detected in pigs given the formulations.

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Traces of FLBZ and reduced-FLBZ were measured after administration of FLBZ.

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Oral administration of FLBZ-HPBCD solution resulted in a high systemic H-FLBZ exposure.

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Similar FLBZ plasma exposure was observed after parenteral FLBZ-Tween 80 and HPBCD administration.

Pharmacokinetic evaluation of different generic triclabendazole formulations in heifers

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 µg.h/mL) was lower, and for Test III (619.9 µg.h/mL) and Test IV (683.4 µg.h/mL) was higher, than the RF (418.1 µg.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.

Relative bioavailability and comparative clinical efficacy of different ivermectin oral formulations in lambs

Background

Several oral ivermectin (IVM) formulations for use in sheep are available in the pharmaceutical veterinary market in different countries. All of them are indicated at the same dose rate to treat the gastrointestinal nematodes. However, there is a lack of information on the relative systemic exposure (plasma bioavailability) and clinical efficacy among oral formulations routinely used in sheep. The main goal of the work reported here was to perform a pharmaco-parasitological assessment of three different IVM oral formulations in lambs infected with multiple resistant gastrointestinal nematodes. The comparative drug systemic exposure (IVM plasma concentrations) and nematodicidal efficacies (clinical efficacy) in lambs were determined for a reference (RF) and two different test (T1, T2) IVM oral formulations. One hundred and fifty six (n= 156) healthy Corriedale lambs, naturally infected with multiple resistant gastrointestinal nematodes were allocated into four experimental groups (n=39). Animals in each group received treatment (200 μg/kg) with either the RF, one of the test IVM formulations or were kept as untreated control. Blood samples were collected over 15 days post-treatment (n=8). The IVM plasma concentrations were measured by high performance liquid chromatography with fluorescence detection. The faecal nematode egg count reduction test (FECRT) (n=39) and evaluation of the clinical efficacy were performed at day 14 post-treatment (n=6), where a predominance of IVM highly resistant nematodes was observed.

Results and conclusions

Neither the overall kinetic behaviour nor the IVM systemic exposure differed among all the tested oral formulations. Equivalent efficacy results were obtained for the different preparations, with an evident therapeutic failure to control Haemonchus spp. and Teladorsagia circumcincta, which correlates with a high degree of nematode resistance to IVM.

Identification of a field isolate of Fasciola hepatica resistant to albendazole and susceptible to triclabendazole

The experiments described here were designed to characterize the status of susceptibility/resistance to albendazole (ABZ) and triclabendazole (TCBZ) of a Fasciola hepatica isolate (named CEDIVE isolate) recovered from infected sheep (Gualeguay, Argentina) and maintained under laboratory conditions. Two separate clinical efficacy experiments were performed on sheep artificially infected with the CEDIVE isolate. Experiment 1: sheep were randomly distributed either in an untreated control group or in an ABZ (7.5 mg/kg) treated group (n=4 each). Additionally, the systemic exposure of ABZ metabolites was assessed in those ABZ-treated infected animals. In Experiment 2, an untreated control group and a TCBZ (10 mg/kg) treated group was included (n=4 each). The fluckicidal efficacy of ABZ and TCBZ was assessed by the comparison of the number of flukes recovered from untreated and treated sheep at 15 days post-treatment. The efficacy against the CEDIVE isolate of F. hepatica was 29% (ABZ) and 100% (TCBZ). The plasma drug exposure (expressed as AUC and C(max)) observed in the ABZ treated animals (Experiment 1) was in agreement with data obtained in the previous studies, which indicate that the low ABZ efficacy was not related to the quality of the pharmaceutical product and/or to a low systemic availability of the active drug/metabolite. The results reported here clearly show that the CEDIVE isolate of F. hepatica behaves as resistant to ABZ and susceptible to TCBZ.