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The economic impact of gastrointestinal (GI) nematode infections on livestock production is well documented worldwide. Increasing evidence supports the hypothesis that parasite colonization induces significant changes in the GI tract environment and, therefore, in the landscape where the microbiota and parasites occur. Understanding the interactions between bacterial and parasite populations in the digestive tract of livestock may be useful to design parasite control strategies based on microbiota modification. The aims of this work were to investigate the impact of the oxytetracycline-mediated manipulation of the gut microbial community on the composition of GI nematode populations in naturally infected sheep and to explore changes in the GI microbial communities after nematode population treatment with the anthelmintic compound monepantel. Extensive manipulation of the GI microbiota with a therapeutic dose of the long-acting oxytetracycline formulation did not induce significant changes in the GI nematode burden. The gut microbiota of treated animals returned to control levels 17 days after treatment, suggesting strong resilience of the sheep microbial community to antibiotic-mediated microbiota perturbation. A significant decrease of the bacterial Mycoplasmataceae family (Log2FC = -4, Padj = 0.001) and a marked increase of the Methanobacteriaceae family (Log2FC = 2.9, Padj = 0.018) were observed in the abomasum of sheep receiving the monepantel treatment. While a comprehensive evaluation of the interactions among GI mycoplasma, methanobacteria and nematode populations deserves further assessment, the bacteria-nematode population interactions should be included in future control programs in livestock production. Understanding how bacteria and parasites may influence each other in the GI tract environment may substantially contribute to the knowledge of the role of microbiota composition in nematode parasite establishment and the role of the parasites in the microbiota composition., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Mate et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

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.

The combination of the organophosphate (OP) chlorpyrifos (CPF) and the pyrethroid cypermethrin (CPM) is commonly marketed as pour-on formulations for the control of sheep lice, ked, and blowflies. CPF irreversibly inhibits acetylcholinesterases (AChE), while pyrethroids are not AChE inhibitors. However, combinations of pyrethroids with OPs showed a highly synergistic effect on AChE inhibition. Thus, the aim of the current work was to evaluate in vitro and in vivo the inhibitory potency of both pesticides, alone and in combination with AChE and butyrylcholinesterase (BChE) activities in sheep blood. In vitro, IC50 values were similar after CPF or CPF plus CPM incubations. The pour-on coadministration of recommended doses of CPF and CPM did not cause a significant inhibition of AChE and BChE in sheep blood. Only slight percentages of inhibition of their catalytic activities were observed when both drugs were given at 4-fold higher dose rates. The lower systemic availability of topical administration of OPs in sheep may help to explain the lower degree of inhibition of blood AChE and BChE in vivo. The results emerged from this research are a further contribution to the knowledge of the risks of implementing higher dosage regimens of OPs-containing antiparasitic formulations., (© 2019 John Wiley & Sons Ltd.)

The aim of the current work was to evaluate a potential pharmacokinetic interaction between the flukicide triclabendazole (TCBZ) and the broad-spectrum benzimidazole (BZD) anthelmintic oxfendazole (OFZ) in sheep. To this end, both an in vitro assay in microsomal fractions and an in vivo trial in lambs parasitized with Haemonchus contortus resistant to OFZ and its reduced derivative fenbendazole (FBZ) were carried out. Sheep microsomal fractions were incubated together with OFZ, FBZ, TCBZ, or a combination of either FBZ and TCBZ or OFZ and TCBZ. OFZ production was significantly diminished upon coincubation of FBZ and TCBZ, whereas neither FBZ nor OFZ affected the S-oxidation of TCBZ towards its sulfoxide and sulfone metabolites. For the in vivo trial, lambs were treated with OFZ (Vermox ® oral drench at a single dose of 5 mg/kg PO), TCBZ (Fasinex ® oral drench at a single dose of 12 mg/kg PO) or both compounds at a single dose of 5 (Vermox ® ) and 12 mg/kg (Fasinex ® ) PO. Blood samples were taken to quantify drug and metabolite concentrations, and pharmacokinetic parameters were calculated by means of non-compartmental analysis. Results showed that the pharmacokinetic parameters of active molecules and metabolites were not significantly altered upon coadministration. The sole exception was the increase in the mean residence time (MRT) of OFZ and FBZ sulfone upon coadministration, with no significant changes in the remaining pharmacokinetic parameters. This research is a further contribution to the study of metabolic drug-drug interactions that may affect anthelmintic efficacies in ruminants., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Parasitic diseases have a significant impact on livestock production. Nematodicidal drugs, such as fenbendazole (FBZ) or its oxidized metabolite oxfendazole (OFZ), can be used along with the trematodicidal triclabendazole (TCBZ), to broaden the spectrum of anthelmintic activity. However, co-exposure to these compounds could lead to drug-drug (D-D) interactions and eventually alter the clinical profile of each active principle. The aim of this study was to assess the presence of such interactions by means of two in vitro models, namely bovine liver microsomal fractions and bovine precision-cut liver slices (PCLSs). To this end, an in vitro assessment involving incubation of FBZ and TCBZ or a combination of FBZ and TCBZ was carried out. Results with microsomal fractions showed a 78.4% reduction (p = .002) in the rate of OFZ production upon co-incubation, whereas the sulfoxide metabolite of TCBZ (TCBZSO) exhibited a decreasing tendency. With PCLS, OFZ accumulation in the incubation medium increased 1.8-fold upon co-incubation, whereas TCBZSO accumulation decreased by 28%. The accumulation of FBZ and OFZ in the liver tissue increased upon 2-hr co-incubation, from 2.1 ± 1.5 to 18.2 ± 6.1 (p = .0009) and from 0.4 ± 0.1 to 1.3 ± 0.3 nmol (p = .0005), respectively. These results confirm the presence of D-D interactions between FBZ and TCBZ. Further studies are needed to determine the extent of involvement of drug-metabolizing enzymes and membrane transporters in interactions between compounds largely used in livestock production systems., (© 2018 John Wiley & Sons Ltd.)

Background: Soil Transmitted Helminth (STH) infections negatively impact physical and mental development in human populations. Current WHO guidelines recommend morbidity control of these infections through mass drug administration (MDA) using albendazole (ABZ) or mebendazole. Despite major reductions in STH associated morbidity globally, not all programs have demonstrated the expected impact on prevalence of parasite infections. These therapeutic failures may be related to poor programmatic coverage, suboptimal adherence or the exposure of parasites to sub-therapeutic drug concentrations. As part of the DeWorm3 project, we sought to characterize the serum disposition kinetics and pattern of urinary excretion of ABZ and its main metabolites ABZ sulphoxide (ABZSO) and ABZ sulphone (ABZSO2) in humans, and the assessment of the duration and optimal time point where ABZ and/or its metabolites can be measured in urine as an indirect assessment of an individual's adherence to treatment., Methodology/principal Findings: Consecutive venous blood and urine samples were collected from eight (8) human volunteers up to 72 h post-ABZ oral administration. ABZ/metabolites were quantified by HPLC. The ABZSO metabolite was the main analyte recovered both in serum and urine. ABZSO Cmax in serum was 1.20 ± 0.44 μg/mL, reached at 4.75 h post-treatment. In urine, ABZSO Cmax was 3.24 ± 1.51 μg/mL reached at 6.50 h post-ABZ administration., Conclusion/significance: Pharmacokinetic data obtained for ABZ metabolites in serum and urine, including the recovery of the ABZ sulphoxide derivative up to 72 h in both matrixes and the recovery of the amino-ABZ sulphone metabolite in urine samples, are suggesting the possibility of developing a urine based method to assess compliance to ABZ treatment. Such an assay may be useful to optimize ABZ use in human patients., Trial Registration: ClinicalTrials.gov NCT03192449.

1. Precision-cut liver slices (PCLS) from food-producing animals have not been extensively used to study xenobiotic metabolism, and thus information on this field of research is sparse. 2. The aims of the present work were to further validate the technique of production and culture of bovine PCLS and to characterize the metabolic interaction between the anthelmintic albendazole (ABZ) and the flavin-monooxygenase (FMO) inhibitor methimazole (MTZ). 3. Nine steers were used as donors. PCLS were produced and incubated under two methods: a dynamic organ culture (DOC) incubator and a well-plate (WP) system. 4. Tissue viability, assessed through both structural and functional markers, was preserved throughout 12 h of incubation. ABZ was metabolized to its (+) and (-) albendazole sulfoxide stereoisomers (ABZSO) in bovine PCLS. The interaction between ABZ and MTZ resulted in a reduction (p < 0.001) in the rates of appearance of (+) ABZSO. Conversely, in presence of MTZ, the rates of appearance of (-) ABZSO increased under both systems (p < 0.05). 5. Both culture systems were suitable for assessing the interaction between ABZ and MTZ. 6. Overall, the results presented herein show that PCLS are a useful and reliable tool for short-term studies on metabolic drug-drug interactions in the bovine species.

The current work evaluated the inhibitory potency of the herbicide glyphosate (GLP) on acetylcholinesterase (AChE) activity in male and female rat tissues. The AChE activity in brain was higher (p<0.05) than those observed in kidney (females: 2.2-fold; males: 1.9-fold), liver (females: 6-fold; males: 6.9-fold) and plasma (females: 14.7-fold; males: 25.3-fold). Enzyme activities were higher in presence of 10mM GLP compared to those measured at an equimolar concentration of the potent AChE inhibitor dichlorvos (DDVP). Moreover, IC50s for GLP resulted between 6×10(4)- and 6.8×10(5)-fold higher than those observed for DDVP. In conclusion, GLP is a weak inhibitor of AChE in rats., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Progress made in understanding pharmacokinetic behaviour and pharmacodynamic mechanisms of drug action/resistance has allowed deep insights into the pharmacology of the main chemical classes, including some of the few recently discovered anthelmintics. The integration of pharmaco-parasitological research approaches has contributed considerably to the optimization of drug activity, which is relevant to preserve existing and novel active compounds for parasite control in livestock. A remarkable amount of pharmacology-based knowledge has been generated using the sheep abomasal nematode Haemonchus contortus as a model. Relevant fundamental information on the relationship among drug influx/efflux balance (accumulation), biotransformation/detoxification and pharmacological effects in parasitic nematodes for the most traditional anthelmintic chemical families has been obtained by exploiting the advantages of working with H. contortus under in vitro, ex vivo and in vivo experimental conditions. The scientific contributions to the pharmacology of anthelmintic drugs based on the use of H. contortus as a model nematode are summarized in the present chapter., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Solid dispersions (SDs) containing the anthelmintic compound albendazole (ABZ) and either Pluronic 188 (P 188) or polyethylene glycol 6000 (PEG 6000) as hydrophilic carriers were formulated. Drug-polymers interactions in solid state were investigated using different techniques. Only a 4% of total ABZ was dissolved at 5 min post-incubation, reaching dissolution rates of 32.8% (PEG 6000) and 69.4% (P 188) in SDs. In this way, P 188 was substantially more efficient as ABZ dissolution promoter in comparison to PEG 6000, especially at the initial stages of the dissolution processes (<30 min). An increased systemic availability (p < 0.001) was obtained when ABZ was administered as ABZ-P 188 SDs, with a 50% enhancement in systemic exposure (AUC values) compared to treatment with an ABZ suspension. Consistently, the Cmax increased 130% (p < 0.001) following treatment with P 188 based SD ABZ formulation. For the ABZ-PEG 6000 SD formulation, the favorable effect on ABZ systemic availability did not reached statistical significance compared to the control group. The study reported here showed the utility of pharmacokinetic assays performed on mice as a model for preliminary drug formulation screening studies.

Objective: To evaluate the plasma and aqueous humor disposition of prednisolone after oral administration in cats., Methods: Six cats were administered with a single oral dose of prednisolone (10 mg). Blood and aqueous humor samples were serially collected after drug administration. Prednisolone concentrations in plasma and aqueous humor were measured at 0.25, 0.5, 1.0, 1.5, 2.0, 3.0, 4.0, and 5.0 h after administration by a high-performance liquid chromatographic analytical method developed and validated for this purpose., Results: Mean ± standard error (SE) of maximum plasma prednisolone concentration (300.8 ± 67.3 ng/mL) was reached at 1 h after administration. Prednisolone was distributed to the aqueous humor reaching a mean peak concentration of 100.9 ± 25.5 ng/mL at 1.25 h after administration. The mean ± SE systemic and aqueous humor exposure (AUC) was 553.3 ± 120.0 ng h/mL and 378.8 ± 64.9 ng h/mL, respectively. A high AUC(aqueous humor)/AUC(plasma) ratio was observed (0.68 ± 0.13). The mean half-life time of elimination in plasma and aqueous humor was 0.87 ± 0.16 h and 2.25 ± 0.44 h, respectively., Clinical Significance: The observed high ratio between aqueous humor and plasma prednisolone concentrations indicates that extensive penetration of prednisolone to the anterior segment of the eye may occur. This is the first step that contributes to the optimization of the pharmacological therapeutics for the clinical treatment of uveitis.

Topical formulations have achieved worldwide acceptance in veterinary medicine because their administration is an easy, less labor-intensive and nonstressing form. Any chemical compound that comes in contact with the skin has the potential to be locally and/or systemically absorbed. However, many factors related to the features of animal skin, composition of the topical formulation and to the drug itself can determine marked differences in the percutaneous absorption process. The aim of the current work was to characterize the pattern of in vitro percutaneous absorption for moxidectin (MXD) and doramectin (DRM), two of the most worldwide used topical macrocyclic lactone antiparasitic compounds in cattle. The work included the development of a simple and inexpensive in vitro assay useful to predict in vivo drug percutaneous absorption in cattle. Both drugs were administered as the commercial formulations intended for their topical administration to cattle. The in vitro studies were carried out using modified Franz-type vertical diffusion cells. Cattle skin slices of 500 μm thickness were prepared using a dermatome to separate the stratum corneum and upper epidermis from dermis and subcutaneous tissue. The receptor medium was sampled up to 72 h postadministration and drug concentrations were measured by HPLC. The parameters used to estimate the comparative in vitro skin permeation showed marked differences between DRM and MXD. A 5.29-fold longer lag time (T(lag)) was observed for DRM. Similarly, the flux (J) (2.93-fold) and the permeation coefficients (K(p) ) (2.95-fold) in cattle skin were significantly higher (P < 0.05) for DRM compared to those obtained for MXD. Additionally, the data obtained from the in vitro permeation studies was correlated with the plasma concentrations of both compounds achieved in vivo in cattle treated with the same topical formulations. Correlation coefficients between percentage of drug permeated in vitro vs. percentage of drug absorbed in vivo (up to 48 h post-treatment) were 0.856-0.887 (MXD) and 0.976-0.990 (DRM). However, the highest in vitro-in vivo correlations for both molecules were observed up to 24 h post-treatment A rapid screening method for testing different topical formulations can be achieved with the simple in vitro cattle skin permeation technique described here, which has been successfully adapted to test the comparative percutaneous absorption of MXD and DRM., (© 2011 Blackwell Publishing Ltd.)

An in vivo study in the laboratory rat model has been carried out to monitor morphological changes in adult Fasciola hepatica over a 4-day period resulting from co-treatment with triclabendazole (TCBZ) and ketoconazole (KTZ), a cytochrome P450 inhibitor. Rats were infected with the triclabendazole-resistant Oberon isolate of F. hepatica, dosed orally with triclabendazole at a dosage of 10mg/kg live weight and ketoconazole at a dosage of 10mg/kg live weight. Flukes were recovered at 24, 48, 72 and 96 h post-treatment (p.t.) and changes to fluke ultrastructure were assessed using transmission electron microscopy (TEM). Results showed an increase in the severity of changes to the fluke ultrastructure with time p.t. Swelling of the basal infolds and the associated mucopolysaccharide masses became more severe with time. Golgi complexes, if present, were greatly reduced in size and number by 96 h p.t., and sub-tegumental flooding was seen from the 72 h time-period onwards. Some sloughing of the tegumental covering over the spines was observed at 96 h p.t. The results demonstrated that the Oberon isolate is more sensitive to TCBZ action in the presence of KTZ than to TCBZ alone, reinforcing the idea that altered drug metabolism is involved in the resistance mechanism. Moreover, they support the concept that TCBZ+inhibitor combinations (aimed at altering drug pharmacokinetics and potentiating the action of TCBZ) could be used in the treatment of TCBZ-R populations of F. hepatica., (© 2011 Elsevier B.V. All rights reserved.)

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The cytochrome P450 (CYP 450) enzyme pathway was inhibited using ketoconazole (KTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP 450 system was inhibited by a 2-h pre-incubation in ketoconazole (40 μM), then incubated for a further 22 h in NCTC medium containing either KTZ, KTZ + nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM), KTZ + NADPH + TCBZ (15 μg/ml), or KTZ + NADPH + triclabendazole sulphoxide (TCBZ.SO; 15 μg/ml). Changes to fluke ultrastructure following drug treatment and metabolic inhibition were assessed using transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than TCBZ-resistant isolate. However, co-incubation with KTZ + TCBZ, but more particularly KTZ + TCBZ.SO, led to more severe changes to the TCBZ-resistant isolate than with each drug on its own: for example, there was severe swelling of the basal infolds and their associated mucopolysaccharide masses, accompanied by an accumulation of secretory bodies just below the apex. Golgi complexes were greatly reduced or absent in the tegumental cells and the synthesis, production, and transport of secretory bodies were badly disrupted. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action. The results support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The cytochrome P450 (CYP 450) enzyme pathway was inhibited using ketoconazole (KTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP 450 system was inhibited by a 2-h pre-incubation in ketoconazole (40 μM), then incubated for a further 22 h in NCTC medium containing either KTZ, KTZ + nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM), KTZ + NADPH + TCBZ (15 μg/ml), or KTZ + NADPH + triclabendazole sulphoxide (TCBZ.SO; 15 μg/ml). Changes to fluke ultrastructure following drug treatment and metabolic inhibition were assessed using transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than TCBZ-resistant isolate. However, co-incubation with KTZ + TCBZ, but more particularly KTZ + TCBZ.SO, led to more severe changes to the TCBZ-resistant isolate than with each drug on its own: in the syncytium, for example, there was severe swelling of the basal infolds and their associated mucopolysaccharide masses, accompanied by an accumulation of secretory bodies just below the apex. Golgi complexes were greatly reduced or absent in the tegumental cells and the synthesis, production, and transport of secretory bodies were badly disrupted. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action. The results support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

An in vivo study in the laboratory rat model was carried out to monitor morphological changes in adult Fasciola hepatica over a 4-day period resulting from combination treatment of triclabendazole (TCBZ) and the metabolic inhibitor, ketoconazole (KTZ). Rats were infected with the TCBZ-resistant Oberon isolate of F. hepatica and divided into 3 groups at 12 weeks post-infection. The first group was dosed orally with TCBZ at a dosage of 10mg/kg and KTZ at a dosage of 10mg/kg. Flukes were recovered at 24, 48, 72 and 96 h post-treatment (p.t.). A second group of rats was treated with TCBZ alone (10mg/kg) and sacrificed at 96 h p.t. The third group acted as untreated controls. Surface changes were monitored by scanning electron microscopy (SEM). In flukes from the TCBZ+KTZ-treated group, the results showed a progressive and time-dependent increase in the level of disruption to the tegumental syncytium. Swelling, furrowing, blebbing and sloughing of the syncytium increased with time p.t. Another feature seen was a thick layer of tegumental shedding in some fluke samples at different times p.t. By comparison, flukes treated with TCBZ alone remained unaffected. The results demonstrated that the Oberon isolate is only sensitive to drug action in the presence of ketoconazole, indicating that combining triclabendazole with a metabolic inhibitor could be used to preserve the effectiveness of the drug against TCBZ-resistant populations of F. hepatica., (Copyright © 2010 Elsevier B.V. All rights reserved.)

A study has been carried out to determine whether the action of triclabendazole (TCBZ) against the liver fluke, Fasciola hepatica is altered by inhibition of the cytochrome P450 (CYP 450)-mediated drug metabolism pathway. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible fluke isolates were used for these experiments, the basic design of which is given in the paper by Devine et al. (2010a). Piperonyl butoxide (PB) was the CYP P450 inhibitor used. Morphological changes resulting from drug treatment and following metabolic inhibition were assessed by means of transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than TCBZ-resistant isolate. However, co-incubation with PB+TCBZ, but more particularly PB+TCBZ.SO, led to greater changes to the TCBZ-resistant isolate than with each drug on its own, with blebbing of the apical plasma membrane, severe swelling of the basal infolds and their associated mucopolysaccharide masses in the syncytium and flooding in the internal tissues. Golgi complexes were greatly reduced or absent in the tegumental cells and the synthesis and production of secretory bodies were badly disrupted. The mitochondria were swollen throughout the tegumental system and the somatic muscle blocks were disrupted. With the TCBZ-susceptible Cullompton isolate, there was a limited increase in drug action following co-incubation with PB. The results provide evidence that the condition of a TCBZ-resistant fluke can be altered by inhibition of drug metabolism. Moreover, they support the concept that altered drug metabolism contributes to the mechanism of resistance to TCBZ.

Solids dispersions (SDs) have been proposed as an alternative to improve the dissolution rate of low solubility drugs. SDs containing albendazole (ABZ; 5, 10, 25, and 50% w/w) and Pluronic 188 (P 188) as hydrophilic carrier were formulated. The obtained SDs were assessed in comparison to physical mixtures (PMs). Drug-polymer interactions in solid state were investigated using Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. No chemical interaction was found between ABZ and poloxamer. The dissolution profiles indicated that ABZ incorporated in SDs and PMs was rapidly released, reaching rapidly the steady state. Increased dissolution rates are usually observed at the highest polymer proportions. However, an opposite effect for SDs as well as for PMs was observed in the assays described here. The systems with the lowest P 188 percentages (SD4, SD3; PM4, PM3) tended to be more effective in increasing the ABZ dissolution rate. Such a result can be attributed to the fact that concentrated aqueous solutions of Poloxamer may form thermo-reversible gels. The physical-mechanical properties indicated that SDs possess improved flow and compacting properties compared to PMs. Thus, ABZ SDs would be more convenient for solid dosage form design and manufacture.

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) is altered by using the metabolic inhibitor, ketoconazole (KTZ) to inhibit the cytochrome P450 (CYP 450) system within Fasciola hepatica. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP 450 enzyme system was inhibited by a 2 h pre-incubation in KTZ (40 microM). Flukes were then incubated for a further 22 h in NCTC medium containing either KTZ; KTZ + nicotinamide adenine dinucleotide phosphate (NADPH; 1 nM); KTZ + NADPH + TCBZ (15 microg/ml); or KTZ + NADPH + triclabendazole sulphoxide (TCBZ.SO;15 microg/ml). Morphological changes resulting from drug treatment and following metabolic inhibition were assessed using scanning electron microscopy. After treatment with either TCBZ or TCBZ.SO alone, there was greater disruption to the TCBZ-susceptible isolate than the TCBZ-resistant isolate. However, co-incubation with KTZ and TCBZ/TCBZ.SO led to more severe surface changes to the TCBZ-resistant isolate than with each drug on its own, with greater swelling and blebbing of the tegument and even the loss of the apical plasma membrane in places. With the Cullompton isolate, there was limited potentiation of drug action in combination with KTZ, and only with TCBZ.SO. The results support the concept of altered drug metabolism within TCBZ-resistant isolates and indicate that this process may play a role in the development of drug resistance.

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The flavin monooxygenase system (FMO) was inhibited using methimazole (MTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The FMO system was inhibited by a 2-h pre-incubation in methimazole (100 microM), then incubated for a further 22 h in NCTC medium containing either MTZ; MTZ+nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM); MTZ+NADPH+TCBZ (15 microg/ml); or MTZ+NADPH+triclabendazole sulphoxide (TCBZ.SO) (15 microg/ml). Changes to fluke ultrastructure following drug treatment and metabolic inhibition were assessed using transmission electron microscopy. After treatment with either TCBZ or TCBZ.SO on their own, there was greater disruption to the TCBZ-susceptible than triclabedazole-resistant isolate. However, co-incubation with MTZ+TCBZ, but more particularly MTZ+TCBZ.SO, led to more severe changes to the TCBZ-resistant isolate than with each drug on its own, with severe swelling of the basal infolds and mucopolysaccharide masses in the syncytium, accompanied by a reduction in numbers of secretory bodies. The synthesis and production of secretory bodies in the tegumental cells was severely affected as well. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action. The results support the concept of altered drug metabolism in TCBZ-resistant flukes, and this process may play a role in the development of drug resistance.

A study has been carried out to investigate whether the action of triclabendazole (TCBZ) against Fasciola hepatica is altered by inhibition of drug metabolism. The cytochrome P450 (CYP P450) system was inhibited using piperonyl butoxide (PB). The Oberon TCBZ-resistant and Cullompton TCBZ-susceptible isolates were used for these experiments. The CYP P450 system was inhibited by a 2 h pre-incubation in PB (100 mum). Flukes were then incubated for a further 22 h in NCTC medium containing either PB; PB+nicotinamide adenine dinucleotide phosphate (NADPH) (1 nm); PB+NADPH+TCBZ (15 microg/ml); or PB+NADPH+TCBZ.SO (15 microg/ml). Morphological changes resulting from drug treatment and following metabolic inhibition were assessed using scanning electron microscopy. After treatment with either TCBZ or TCBZ.SO alone, there was greater disruption to the TCBZ-susceptible than the resistant isolate. However, co-incubation with PB and TCBZ/TCBZ.SO lead to more severe surface changes to the TCBZ-resistant Oberon isolate than with each drug on its own. With the TCBZ-susceptible Cullompton isolate, there was limited potentiation of drug action, and only with TCBZ.SO. The results support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

Albendazole and fenbendazole are methylcarbamate benzimidazole anthelmintics extensively used to control gastrointestinal parasites in domestic animals. These parent compounds are metabolised to albendazole sulfoxide and fenbendazole sulfoxide (oxfendazole), respectively. Both sulfoxide derivatives are anthelmintically active and are manufactured for use in animals. They metabolites have an asymmetric centre on their chemical structures and two enantiomeric forms of each sulfoxide have been identified in plasma, tissues of parasite location and within target helminths. Both the flavin-monooxygenase and cytochrome P450 systems are involved in the enantioselective biotransformation of these anthelmintic compounds in ruminant species. A relevant progress on the understanding of the relationship among enantioselective metabolism and systemic availability of each enantiomeric form has been achieved. This article reviews the current knowledge on the pharmacological implications of the enantiomeric behaviour of albendazole sulfoxide and oxfendazole in domestic animals.

Dung invertebrate colonization and degradation levels of faeces from cattle treated with endectocides were studied. Faeces of control and doramectin (DRM) (subcutaneous) and moxidectin (MXD) (subcutaneous and topical) treated animals were deposited on the field from 3 to 21 days post-treatment (pt). Pats were recovered after 6 to 42 days post-deposition (pd). Faecal weight, dry matter, arthropods number, and drugs concentrations were determined. Total arthropods number was higher in control (P<0.0001) than in the other groups from days 3 to 21 pt. Total number of insects recovered on days 3, 11, and 21 pt from control pats was significantly (P<0.001) higher than in treated-animal pats during all the trial. At day 21 pt, the insects' number in dung voided by DRM-treated cattle was (P<0.05) lower than in the other groups. Comparisons of dung degradation among treatments were inconclusive. A lower adverse effect was observed for MXD compared with DRM. No significant degradation of MXD or DRM was observed during the present trial.

Summary: A study has been carried out to investigate whether the action of triclabendazole (TCBZ) is altered in the presence of a metabolic inhibitor. The flavin monooxygenase system (FMO) was inhibited using methimazole (MTZ) to see whether a TCBZ-resistant isolate could be made more sensitive to TCBZ action. The Oberon TCBZ-resistant and Cullompton TCBZ-sensitive isolates were used for these experiments. The FMO system was inhibited by a 2-h pre-incubation in methimazole (100 microM). Flukes were then incubated for a further 22 h in NCTC medium containing either MTZ; MTZ+nicotinamide adenine dinucleotide phosphate (NADPH) (1 nM); MTZ+NADPH+TCBZ (15 microg/ml); or MTZ+NADPH+triclabendazole sulphoxide (TCBZ.SO) (15 microg/ml). Morphological changes resulting from drug treatment and following metabolic inhibition were assessed using scanning electron microscopy. After treatment with either TCBZ or TCBZ.SO alone, there was greater surface disruption to the triclabendazole-susceptible than -resistant isolate. However, co-incubation with MTZ and TCBZ/TCBZ.SO lead to more severe surface changes to the TCBZ-resistant isolate than with each drug on its own; this was not seen for the TCBZ-susceptible Cullompton isolate. Results of this study support the concept of altered drug metabolism in TCBZ-resistant flukes and this process may play a role in the development of drug resistance.

The pharmacokinetics of an anthelmintic drug includes the time course of drug absorption, distribution, metabolism and elimination from the host and determines the concentration of the active drug that reaches the location of the parasite. However, the action of the anthelmintic also depends on the ability of the active drug to reach its specific receptor within the target parasite. Thus, drug entry and accumulation in target helminths are important issues when considering how best to achieve optimal efficacy. Passive drug transfer through the external helminth surface is the predominant entry mechanism for most widely used anthelmintics and is discussed in this article. Despite the structural differences between the external surface of nematodes (the cuticle) and the external surface of cestodes and trematodes (the tegument), the mechanism of drug entrance into both types of helminth depends on the lipophilicity of the anthelmintic and this is the major physicochemical determinant for the drug to reach a therapeutic concentration in the target parasite. Understanding the processes that regulate drug transfer into helminth parasites is an important aspect in improving the control of parasites in human and veterinary medicine.

Triclabendazole (TCBZ) is a halogenated benzimidazole compound that possesses high activity against immature and adult stages of the liver fluke, Fasciola hepatica. The intensive use of TCBZ in endemic areas of fascioliasis has resulted in the development of liver flukes resistant to this compound. TCBZ sulphoxide (TCBZSO) and TCBZ sulphone (TCBZSO2) are the main molecules recovered in the bloodstream of TCBZ-treated animals. In order to gain some insight into the possible mechanisms of resistance to TCBZ, the goals of the work described here were: to compare the ex vivo transtegumental diffusion of TCBZ parent drug and its sulpho-metabolites (TCBZSO and TCBZSO2) into TCBZ-susceptible and -resistant liver flukes; and to assess the comparative pattern of TCBZ biotransformation by TCBZ-susceptible and -resistant F. hepatica. For the tegumental diffusion studies, TCBZ-susceptible (Cullompton) and -resistant (Sligo) adult flukes collected from untreated infected sheep were incubated (15-180 min) in KRT buffer containing either TCBZ, TCBZSO or TCBZSO2 (5 nmol.ml-1). For the metabolism studies, microsomal fractions obtained from TCBZ-susceptible and -resistant flukes were incubated for 60 min with TCBZ (40 microM), and the amount of the formed metabolic product (TCBZSO) was measured. Drug/metabolite concentrations were quantified by HPLC. All the assayed TCBZ-related molecules penetrated through the tegument of both TCBZ-susceptible and -resistant flukes. However, significantly lower (approximately 50%) concentrations of TCBZ and TCBZSO were recovered within the TCBZ-resistant flukes compared to the TCBZ-susceptible ones over the 180 min incubation period. The rate of TCBZ sulphoxidative metabolism into TCBZSO was significantly higher (39%) in TCBZ-resistant flukes. The flavin-monooxigenase (FMO) enzyme system appears to be the main metabolic pathway involved in the formation of TCBZSO in both TCBZ-susceptible and -resistant flukes. The altered drug influx/efflux and enhanced metabolic capacity identified in TCBZ-resistant liver flukes may account for the development of resistance to TCBZ.

Reasons for Performing the Study: The study of novel pharmacological strategies to control parasitism in horses is required since many parasite species have developed resistance to anthelmintic drugs., Objectives: To evaluate the effects of piperonyl butoxide (PB) (a metabolic inhibitor) on the plasma availability and enantiomeric behaviour of oxfendazole (OFZ) given orally to horses, and to compare the clinical efficacy of OFZ given either alone or co-administered with PB in naturally parasitised horses., Methods: Fifteen naturally parasitised crossbred male ponies were allocated into 3 groups (n = 5) and treated orally as follows: Group I (control) received distilled water as placebo; Group II was dosed with OFZ (10 mg/kg bwt); and Group III was treated with OFZ (10 mg/kg bwt) co-administered with PB (63 mg/kg bwt). Jugular blood samples were obtained over 120 h post treatment. Three weeks after treatments, all experimental horses were subjected to euthanasia., Results: The observed maximum plasma concentration (Cmax) and area under the concentration vs. time curve (AUC) values for OFZ increased 3- and 5-fold, respectively, in the presence of PB. The plasma concentration profiles of fenbendazole (FBZ), a metabolite generated from OFZ, were significantly lower after the treatment with OFZ alone (AUC = 0.8 microg x h/ml) compared to those obtained after the OFZ + PB treatment (AUC = 2.7 microg x h/ml). The enhanced pharmacokinetic profiles correlated with increased anthelmintic efficacy. The combination OFZ + PB showed 100% efficacy against mature nematode parasites. The efficacy against cyathostome L3 larvae increased from 94% (Group II) to 98.7% (Group III). Consistently, the number of L4 larvae recovered from OFZ + PB treated horses (Group III) (n = 146) was significantly lower (P<0.05) than that recovered from Group II (n = 1397)., Conclusions: The use of PB as a metabolic inhibitor may be useful to enhance OFZ activity against mature and migrating larvae of different parasite species in horses., Potential Relevance: Metabolic inhibitors may be used to enhance the activity of benzimidazole anthelmintics and extend the effective lifespan of benzimidazole drugs in the face of increasing resistance.

Ivermectin (IVM) and moxidectin (MXD) are broad-spectrum endectocide antiparasitic drugs extensively used in food-producing animals. The patterns of IVM and MXD excretion in milk were comparatively characterized following their subcutaneous administration (200 microg.kg(-1) of body weight) to lactating dairy sheep. The relationship between milk excretion and plasma disposition kinetics of both compounds was characterized. A pool of milk collected from all of the animals in each experimental group was used for cheese elaboration. IVM and MXD residual concentrations were assessed during the cheese-making process and ripening period. IVM and MXD concentrations were measured in plasma, milk, and milk product (whey, curd, and cheese) samples using an HPLC-based methodology with fluorescence detection. IVM and MXD were extensively distributed from the bloodstream to the mammary gland, and large quantities, particularly of MXD, were excreted in milk. Residual concentrations of both compounds were recovered in milk up to 30 (IVM) and 35 (MXD) days post-treatment. The total fraction of the administered dose excreted in milk for MXD was significantly higher than that of IVM. During cheese production, the highest residual concentrations of both molecules were measured in the curd. Thirty-four percent of the total drug residue measured in the pooled milk collected from treated sheep was lost during the cheese-making process. The lowest residual concentrations were measured in the whey. IVM and MXD concentrations in the elaborated cheese tended to increase during the ripening period, reaching the highest residual level at 40 days of cheese maturation. The long persistence of milk residual concentrations of MXD and IVM in lactating dairy sheep and the high concentrations found in cheese and other milk-related products should be seriously considered before recommendation of the extralabel use of these antiparasitic drugs in dairy animals.

The work reported here describes the comparative ability of albendazole (ABZ), fenbendazole (FBZ) and triclabendazole (TCBZ) to penetrate through the tegument of mature Fasciola hepatica, and the influence of the physicochemical composition of the incubation medium on the drug diffusion process. The data obtained from the trans-tegumental diffusion kinetic studies were complemented with the determination of lipid-to-water partition coefficients (octanol-water) for the benzimidazole (BZD) anthelmintic drugs assayed. Sixteen-week-old F. hepatica were obtained from untreated artificially infected sheep. The flukes were incubated (37 degrees C) over 60 and 90 min in incubation media (pH 7.4) prepared with different proportions of ovine bile and Krebs' Ringer Tris (KRT) buffer (100, 75, 50, 25 and 0% of bile) containing either ABZ, FBZ or TCBZ at a final concentration of 5 nmol/ml. After the incubation time expired, the liver fluke material was chemically processed and analysed by high performance liquid chromatography (HPLC) to measure drug concentrations within the parasite. Additionally, the octanol-water partition coefficients (PC) for each molecule were calculated (as an indicator of drug lipophilicity) using reversed phase HPLC. The 3 BZD molecules were recovered from F. hepatica at both incubation times in all incubation media assayed. The trans-tegumental diffusion of the most lipophilic molecules ABZ and FBZ (higher PC values) tended to be greater than that observed for TCBZ. Interestingly, the uptake of ABZ by the liver flukes was significantly greater than that measured for TCBZ, the most widely used flukicidal BZD compound. This differential uptake pattern may be a relevant issue to be considered to deal with TCBZ-resistant flukes. Drug concentrations measured within the parasite were lower in the incubations containing the highest bile proportions. The highest total availabilities of the 3 compounds were obtained in liver flukes incubated in the absence of bile. Altogether, these findings demonstrated that the entry of the drug into a target parasite may not only depend on a concentration gradient, the lipophilicity of the molecule and absorption surface, but also on the physicochemical composition of the parasite's surrounding environment.

Ivermectin (IVM) is a broad-spectrum antiparasitic drug extensively used in human and veterinary medicine that is largely excreted in bile and faeces. Loperamide (LPM) is an opioid derivative that reduces gastrointestinal secretions and motility. Both IVM and LPM have been reported to act as P-glycoprotein substrates (P-GP). The goal of the present work was to study the LPM-induced modifications to the pattern of tissue distribution for IVM. Thirty-six Wistar male rats were randomly allocated to two groups (n = 18) and treated subcutaneously with IVM alone or co-administered with LPM. Rats were killed at different times post-treatment and samples (blood and tissues) were collected and analyzed by HPLC. The presence of LPM induced a marked enhancement in the IVM plasma concentrations, resulting in a significantly higher area under concentration time curve (AUC) value (P < 0.01) than that obtained after the administration of IVM alone. Significantly higher IVM availabilities in the liver tissue and small intestine wall (P < 0.05) were obtained in the presence of LPM. There were no statistically significant differences in drug availability in the large intestinal wall after both treatments. However, LPM induced a marked decrease in the amount of IVM recovered in the large intestinal lumen content. The ratio between IVM concentrations in the large intestinal luminal content and plasma at day 1 post-treatment was 4.64-fold higher in the absence of LPM. The delayed intestinal transit time caused by LPM accounting for an extended plasma-intestine recycling time, and a potential competition between IVM and LPM for the P-GP-mediated bile-intestinal secretion processes, may account for the enhanced IVM systemic availability reported in the current study.

This work characterized the effects of albendazole sulphoxide (ABZSO) on placental and fetal parameters in Wistar rats on day 20 of gestation. ABZSO was fed in laboratory chow at 0, 2.5, 5, 10, 20 or 30 mg/kg/d from day 6 to 15 of gestation to pregnant rats. Data of resorptions, placental and fetal characteristics and fetal skeletal malformations were recorded. Resorption percentages in the 20 and 30 mg/kg/d groups were significantly higher compared to the control group. Placentas of ABZSO-treated rats had lower weight and smaller size than untreated rats. The fetal weight and size were lower in the 5 mg/kg/d dose compared to no treatment. In the 5, 10 and 20 mg/kg/d groups, reductions in ossification process were observed. ABZSO induced malformations and/or fetal death when orally administered to pregnant rats. This data contributes to characterization of the reproductive toxicity of ABZSO, the main active metabolite of albendazole.

Doramectin (DRM) is a broad spectrum macrocyclic lactone antiparasitic drug not approved for use in dairy animals. However, DRM and other endectocide compounds are widely used extra-label to control endo- and ectoparasites in dairy sheep. The plasma disposition kinetics and the pattern of DRM excretion in milk were characterized following its subcutaneous administration to lactating dairy sheep. DRM concentration profiles were measured in plasma and milk samples after validation of a specific HPLC-based methodology. DRM was detected between 1 h and 30 days post-treatment. DRM concentrations of 0.48 ng.mL(-1) (plasma) and 1.03 ng.mL(-1) (milk) were measured at 30 days post-treatment. DRM was extensively distributed from the bloodstream to the mammary gland, and large concentrations were excreted in milk. The peak concentrations and total amount of DRM recovered in milk (expressed as area under the concentration versus time curve) were 3-fold higher than those measured in plasma; 2.44% of the total DRM dose was excreted in milk. The long persistence of DRM milk residues should be seriously considered before its extra-label use in dairy animals is recommended.

The experiments described here report on the correlation between the ex vivo diffusion of different benzimidazole (BZD) anthelmintics into the cestode parasite Moniezia benedeni, and their octanol-water partition coefficients (P.C.). The characterisation of the drug diffusion process into target parasites is relevant to understand the mechanism of drug penetration and the pharmacological activity of anthelmintic drugs. Specimens of the tapeworm M. benedeni, used as a helminth parasite model, were obtained from untreated cattle killed at the local abattoir. The collected parasites were incubated (5-210 min) with either fenbendazole (FBZ), albendazole (ABZ), ricobendazole (RBZ), oxfendazole (OFZ), mebendazole (MBZ), oxibendazole (OBZ), or thiabendazole (TBZ), in a Kreb's Ringer Tris buffer medium at a final concentration of 5 nmol/ml. After the incubation time elapsed, samples of parasite material were chemically extracted and prepared for high performance liquid chromatography (HPLC) analysis to measure drug/metabolite concentrations. Additionally, the octanol-water P.C. for each molecule was estimated as an indicator of drug lipophilicity, using reversed phase HPLC analysis. All the incubated drugs were recovered from the tapeworms as early as 5 min post incubation. There was a high correlation (r=0.87) between drug lipophilicity, expressed as octanol-water P.C. (Log P), and drug availability within the parasite. The most lipophilic BZD compounds (FBZ, ABZ, and MBZ), with P.C. values higher than 3.7, were measured at significative higher concentrations within the tapeworm compared to those drugs with the lowest P.C. values. Considering the results from the current and previous studies, it is clear that passive diffusion is a major mechanism of BZD penetration into cestode parasites, where lipid solubility is a determinant factor influencing the diffusion of these anthelmintic molecules through the parasite tegument.

The pharmacological effect of the active albendazole metabolite, albendazole sulphoxide (ABZSO), depends on its sustained presence at the site of parasite location and its binding to helmith beta-tubulin. ABZSO is found in the plasma and tissues of albendazole-treated animals in two enantiomeric forms: (+)ABZSO and (-)ABZSO. Knowledge of enantioselectivity in drug action is necessary, since any difference in target proteins affinity between enantiomers may have implications on the pharmacological effect of this anthelmintic molecule. The binding of ABZSO to mammalian and helminth parasites cytosolic proteins, as well as the differential binding of both enantiomers, were studied. Cytosolic proteins from Moniezia expansa (cestode), Ascaris suum (nematode), Fasciola hepatica (trematode), rat liver and brain as well as purified porcine brain tubulin were used. Drug analysis was performed by HPLC using both C18 and chiral columns. ABZSO protein binding was quantitatively different between parasite species (4.17, 2.5 and 1.07 ng/mg for cestode, nematode and trematode, respectively); this binding to helminth cytosolic proteins was enantioselective. Enantiomeric ratios of (-)ABZSO/(+)ABZSO as a percentage were: 43/57 (Ascaris), 36/64 (Moniezia) and 91/9 (Fasciola). Conversely, the binding of ABZSO to mammalian cytosolic proteins showed no enantioselectivity. The overall binding affinity of ABZSO for mammalian cytosolic proteins was lower than that observed in helminth proteins. The characterization of the comparative binding pattern of ABZSO enantiomers to cytosolic proteins from helminth parasites and mammalian tissues may contribute to understanding the pharmacological properties of this chiral anthelmintic molecule.

The current experiments compare the pattern of ex vivo uptake (diffusion) of albendazole (ABZ) and albendazole sulfoxide (ABZSO) by Ascaris suum and Fasciola hepatica. Specimens of A. suum and F. hepatica were collected from untreated animals (pigs and sheep, respectively) and incubated with either ABZ or ABZSO for different time periods (5-180 min). After incubation. the parasite material was analysed by HPLC to quantify the amount of ABZ and/or ABZSO. The parent drug and its active ABZSO metabolite were recovered from the parasites after ex vivo incubation for different time periods throughout the assay. Total drug availability in A. suum, expressed as area under the concentration versus time curve (AUC) over 180 min of incubation, was significantly greater (P<0.05) for ABZ parent drug (AUC = 4.19 +/- 0.59 microg x h xg(-1)) compared with the more polar ABZSO metabolite (AUC = 0.25 +/- 0.01 micro x h x g(-1)). Similar results were observed after the incubation of both molecules with F. hepatica, where the AUC values obtained were 10.6 +/- 0.28 microg x h x g(-1) and 2.04 +/- 0.33 microg x h x g(-1) for ABZ and ABZSO, respectively. The greater diffusion and availability of ABZ in both helminths correlate with the higher lipophilicity of the parent drug, compared with its sulfoxide metabolite. The amount of both molecules measured in A. suum was significantly lower (P<0.05) than that recovered in F. hepatica. The complexity of the histological structure of the nematode cuticle compared with the external tegument of the trematode may account for such a difference in drug diffusion between the species. These findings complement previous observations on the patterns of in vivo uptake of ABZ by different helminth parasites, contributing to the understanding of the pharmacological anthelmintic action of these moieties.

Albendazole (ABZ) is a broad-spectrum benzimidazole anthelmintic widely used in human and veterinary medicine. The aim of the current work was to characterise the sulphoxidative metabolism of ABZ, and the sulphoreduction of ABZ sulphoxide (ABZSO), by microsomal (Ms) and cytosolic (Cyt) fractions of three different helminth species: Fasciola hepatica, Moniezia expansa and Ascaris suum. After the incubation assays, parasite material was analysed by HPLC to characterise the metabolic product formed. Both the Ms and Cyt fractions of the three parasites studied were able to oxidise ABZ into ABZSO in a non-enantioselective fashion. Oxidation of ABZ was greater in the Ms fraction of the trematode (50%) than in both cestode (19%) and nematode (14%) parasites. Only the incubation of ABZSO with both subcellular fractions of M. expansa generated ABZ as a metabolic product. The results obtained here indicate that helminths have the capacity to biotransform benzimidazole compounds; however, this metabolic activity differs qualitatively and quantitatively among helminth species.

The pattern of in vivo uptake of albendazole (ABZ) and its major metabolite, ABZ-sulphoxide (ABZSO), by Haemonchus contortus and Fasciola hepatica recovered from ABZ-treated sheep, was investigated. Concentration profiles of both compounds were simultaneously measured in target tissues/fluids from the same infected sheep. In addition, the proportion of the (+) and (-) ABZSO enantiomers was determined in plasma, bile and F. hepatica recovered from treated sheep. Sheep naturally infected with H. contortus were intraruminally (i.r.) treated with ABZ (micronized suspension, 7. 5mg/kg) and the plasma concentrations of ABZSO and ABZ-sulphone (ABZSO(2)) determined in addition to the concentration of ABZ and ABZSO in H. contortus, abomasal mucosa and fluid content samples. In addition, F. hepatica artificially infected sheep were treated i.r. with the same ABZ suspension (7.5mg/kg), and samples of blood, bile, liver tissue and adult flukes were collected and analysed by HPLC to determine the concentrations of ABZ and both enantiomers of ABZSO. ABZSO and ABZSO(2) were the analytes recovered in plasma with ABZ and ABZSO present in H. contortus. ABZ was the analyte recovered at the highest concentration in H. contortus and abomasal mucosa, whereas higher concentrations of ABZSO were measured in abomasal fluid content. Only low concentrations of ABZ were detected in F. hepatica and bile, but markedly higher concentrations of ABZ were measured in liver tissue. ABZSO was the main molecule recovered in F. hepatica, plasma and bile samples collected from ABZ-treated sheep. The (+) enantiomer of ABZSO was recovered at a higher proportion in plasma (75%), bile (78%) and F. hepatica (74%) after ABZ administration to infected sheep.

The enantioselective disposition kinetics of the benzimidazole anthelmintic, ricobendazole (RBZ), have been characterized after its intravenous (iv) and subcutaneous (sc) administration as a racemic formulation to cattle. The (+) and (-) RBZ enantiomeric forms were recovered in plasma after iv and sc administration of the racemic RBZ formulation, using a chiral phase based HPLC method. A biexponential plasma concentration versus time curve was observed for both RBZ enantiomers following the iv treatment. Total body clearance was higher for (-) RBZ (150.4 mL/h. kg) compared with that obtained for the (+) RBZ antipode (78.1 mL/h. kg). The elimination half-life of the (-) RBZ enantiomer was shorter (T1/2beta: 2.67 h) compared with the (+) enantiomer (T1/2beta: 5.41 h). The plasma availability (expressed as AUC) was significantly higher for (+) RBZ compared with that obtained for the (-) antipode following both treatments. The enantiomeric ratio in plasma at T(0) was close to unity (50% of each enantiomer); the analysis of the concentration ratios (+) RBZ/(-) RBZ, demonstrated an increase in the proportion of (+) RBZ during the time course of the kinetics after both iv and sc treatments. The results presented herein show the enantioselective disposition kinetics of RBZ in cattle and are a further contribution to the understanding of the kinetic behaviour of these sulphoxide-containing benzimidazole anthelmintics in ruminants., (Copyright 2000 John Wiley & Sons, Ltd.)

The aim of the present work was to evaluate the effects of methimazole (MTZ) on the enantioselective sulphoxidation of albendazole (ABZ) by rat liver microsomes and tissue slices. Albendazole sulphoxide (ABZSO) was the metabolite recovered after the incubation with ABZ in both liver preparations. MTZ significantly reduced ABZSO production both in microsomes and slices. ABZSO production decreased as a function of MTZ concentration. The sulphoxidation reaction performed by rat liver explants in the presence of MTZ was 65% lower than that observed in controls. The reduction in the production of ABZSO in the presence of MTZ was mainly due to a lower production of (+) ABZSO. The results reported further contribute to the understanding of the enantioselective metabolism of ABZ. In addition, the work presented provides information on the comparison of two different liver tissue preparations for the evaluation of xenobiotic metabolism.

The current experiments correlate the disposition kinetics of albendazole (ABZ) following its intravenous (i.v.) and intraruminal (i.r.) administrations to Moniezia spp.-infected sheep, with the pattern of drug/metabolite uptake by tapeworms collected from treated animals. The ex vivo uptake pattern of ABZ and albendazole sulphoxide (ABZSO) by the same cestode parasite was also investigated. Naturally infected (Moniezia spp.) Corriedale lambs were treated with ABZ by either i.v. (Group A, n = 15) or i.r. (Group B, n = 15) administration at 7.5 mg/kg. Plasma and abomasal fluid samples were obtained over a 120-h period. Two animals per group were killed at 0.5, 1, 2, 4 and 6 h post-treatment; parasite material (tapeworms), bile and intestinal fluid samples were recovered. Furthermore, Moniezia spp. tapeworms obtained from sheep killed at the local abattoir were incubated with either ABZ or ABZSO for different time periods in a Kreb's Ringer Tris buffer (ex vivo experiments). Samples were analysed by high performance liquid chromatography for ABZ, ABZSO and albendazole sulphone (ABZSO2). ABZ plasma concentrations decreased rapidly and were not detectable beyond 10 h following i.v. administration. ABZSO and ABZSO2 were the metabolites recovered in plasma after both treatments. ABZ and its metabolites were extensively distributed to the digestive tract, mainly into the abomasal fluid, after the i.v. and i.r. administrations. The parent drug and its active ABZSO metabolite were recovered in tapeworms collected from both i.v. and i.r. treated lambs. However, the availability of both ABZ and ABZSO was higher in parasite material recovered from i.v. treated animals. The uptake of ABZ by the cestode parasite, both in vivo and ex vivo, was significantly greater than that of its sulphoxide metabolite, which agrees with the higher lipophilicity of the parent drug.

The development of drug resistance and the inability of the drug to reach the location of the etiologic agents are major challenges for anti-infective and cancer therapies. As the development of new drugs with improved pharmacodynamic and pharmacokinetic properties is a slow and difficult process, drug delivery systems appear as promising alternatives. Liposomes are lipid vesicles formed when phospholipids are exposed to an aqueous environment. They arrange themselves in bilayers and close up, forming a vesicle. During this process they capture the aqueous phase of the dispersion, and any substance dissolved in it, within the vesicle. Liposomes have remarkable features that make them an almost ideal delivery system. They are biodegradable, with few side effects, can deliver drugs with different physico-chemical properties together and can be formulated for different routes of administration. The potential to modify the pharmacokinetic behaviour of encapsulated drugs to deliver them selectively to the site of action is the most important feature of liposomes as drug delivery systems. Liposomes are already used in human medicine for he treatment of bacterial, viral and parasitic diseases, and cancer. They have also been proven useful as immunoadjuvants and vaccines. Liposomes are used in certain avian vaccines. The possible uses of liposomes and their impact in veterinary medicine in the treatment of infectious diseases and cancer as well as in the prevention of diseases are discussed in the present article.

The plasma and abomasal fluid disposition kinetics of ricobendazole (RBZ) after subcutaneous (s.c.) administration of a novel injectable formulation to calves, and the comparative plasma availability after s.c. injection of RBZ and that obtained after oral treatment with albendazole (ABZ), were characterised. Six parasite-free Holstein calves received RBZ (solution 150 mg ml(-1)) by s.c. injection at 3.75 mg kg(-1) (Experiment 1). Experiment 2 was conducted in two experimental phases; in phase I, five calves (Group A) received RBZ by s.c. injection and five animals (Group B) were orally treated with ABZ (suspension 100 mg ml(-1)), at 5 mg kg(-1). Drug treatments were reversed for each group in phase II and given at 7.5 mg kg(-1). Samples of abomasal fluid (via cannula) and jugular blood were collected over 72 hours post-treatment and analysed by HPLC. RBZ and its sulphone metabolite were detected in plasma following its s.c. administration. RBZ was rapidly absorbed, reaching the plasma Cmax at 4.5 hours post-dosing. The sulphone metabolite followed a similar kinetic pattern. Both molecules were rapidly and extensively distributed into the abomasum, being detected in abomasal fluid between 30 minutes and 36 hours post-administration. An extensive plasma/abomasum exchange process, with ionic-trapping in the abomasum, accounted for the higher AUC value (>200 per cent) obtained for RBZ in abomasum compared with plasma. The s.c. treatment with RBZ formulated as a solution resulted in a significantly greater plasma availability (measured as ABZ sulphoxide) than the oral treatment with ABZ (suspension) given at the same dose rates.

Albendazole (ABZ) is an anthelmintic benzimidazole drug widely used in human and veterinary medicine. ABZ has binding affinity to both mammalian and helminth parasite tubulin. In the current work, we have performed in vitro assays and in vivo experiments in which rats were given ABZ orally to better characterize the action of the drug on the polymerization of rat brain microtubules and on the detyrosination/tyrosination cycle that occurs on the COOH-terminal end of alpha-tubulin. The results showed that ABZ inhibits brain microtubule polymerization in vitro, and significantly delayed microtubule assembly in vivo. The tyrosination reaction cycle was not affected in vitro; however, in rats to which the drug was administered orally, the levels of in vitro tyrosination were reduced when compared to the controls with mock treatment. These results suggest that this apparent inhibition would be due to a decrease in the amount of substrate caused by the depolymerizing effect of ABZ and the subsequent tyrosination in the intact brain with endogenous tyrosine. In conclusion, ABZ strongly affects tubulin dynamics both in vivo and in vitro. The outcome of these experiments is a contribution to the understanding of the molecular mechanisms involved in the antimicrotubular action of benzimidazole compounds.

The influence of gastrointestinal nematode infection on the kinetics of albendazole (ABZ) and its metabolites, albendazole sulphoxide (ABZSO) and sulphone (ABZSO2) in plasma and abomasal fluid was investigated in sheep. A micronised suspension of ABZ was administered intraruminally at 7.5 mg kg-1 to the following groups of sheep: (a) non-parasitised (control); (b) artificially infected with Haemonchus contortus; (c) naturally infected with Haemonchus contortus and other species of gastrointestinal nematodes. Plasma and abomasal fluid samples were obtained serially over 72 h post-treatment and they were analysed by HPLC for ABZ and its metabolites. The ABZ parent drug was not detected in plasma at any time post-treatment, however the metabolites ABZSO and ABZSO2 were recovered in the bloodstream. The active metabolite ABZSO was recovered in plasma between 0.5 and 48 (uninfected), 60 (H. contortus infected) or 72 h (naturally infected sheep) post-administration. The area under the plasma concentration vs time curve (AUC) values for ABZSO were higher in both artificially infected (64.0 micrograms h ml-1) and naturally infected (79.3 micrograms h ml-1) sheep as compared with non-infected animals (41.8 micrograms h ml-1). Peak plasma concentrations for ABZSO and ABZSO2 were higher in both artificially and naturally infected sheep than in non-parasitised animals. No changes in the half-lives and mean residence times for these metabolites were observed in infected sheep. ABZ and its metabolites were found in the abomasum between 0.5 and 48 (infected animals) or 72 h (uninfected) post-treatment. The availability (total AUCs) of ABZ and its metabolites in abomasal fluid were lower in H. contortus infected sheep than in the uninfected control animals. The increased abomasal pH induced by the presence of the H. contortus infection may reduce the plasma/abomasum pH gradient, which results in a decreased ionic-trapping of ABZ and its metabolites in the abomasum. Such a phenomenon correlates with: (a) the higher total AUC values obtained for ABZ metabolites in the bloodstream of the infected compared to the control sheep, (b) the lower concentration profiles of the ABZ parent drug and its metabolites found in the abomasal fluid of the infected animals.

The influence of fasting on the bioavailability and disposition kinetics of albendazole (ABZ) and its metabolites in cattle was investigated. ABZ (10 mg/ kg) was given by intraruminal (i.r.) (Experiment 1) and intravenous (i.v.) (Experiment 2) administration to Holstein calves either fed ad libitum (control) or subjected to a 48 h fasting period (fasted group) prior to treatment. The rate of passage of digesta through the gastrointestinal (GI) tract was evaluated by measurement of cobalt faecal excretion following the oral administration of the sodium-cobalt-ethylendiamine-tetracetic acid complex to calves subjected to the feeding conditions above described. Jugular blood and abomasal fluid (via cannula) samples were collected over 120 h post-treatment; samples were analysed by high performance liquid chromatography (HPLC) for ABZ, ABZ sulphoxide (ABZSO) and ABZ sulphone (ABZSO2). Fasting the animals prior to the i.r. treatment resulted in pronounced modifications to the plasma and abomasal fluid disposition kinetics of ABZ and its metabolites. A greater extent of GI absorption with significantly higher CmaX (150%) and AUC (310%) values for ABZSO in plasma, was observed in fasted compared to fed animals following the i.r. administration of ABZ. Extended detection of ABZ metabolites resulting in significantly longer plasma t 1/2el and MRT was also obtained in fasted compared to fed calves. These results correlated with the substantially enhanced availability of ABZ and its metabolites (AUCs over 200% greater) in the abomasal fluid of the fasted animals. Fasting did not induce changes to the plasma disposition of either ABZ or its metabolites after the i.v. treatment. The digesta passage rate, measured by the amount of cobalt excreted in faeces, was significantly lower in fasted compared to animals fed ad libitum. A delayed GI transit time that decreases the rate of passage of the drug down the digestive tract, may have accounted for enhanced ABZ dissolution and absorption in fasted compared to fed calves. The findings reported in this article show that fasting prior to treatment notably affects the bioavailability and disposition kinetics of ABZ and its metabolites in cattle.

1. The influence of nutritional status on the plasma and abomasal fluid disposition kinetics of albendazole (ABZ) and its metabolites, albendazole sulphoxide (ABZSO) and albendazole sulphone (ABZSO2), has been investigated in the calf. 2. Free fatty acid (FFA) and beta-hydroxybutyrate (beta-OHB) serum concentrations were significantly higher in the feed-restricted (poor nutritional status) compared with control calf (optimal nutritional status). 3. ABZ parent drug was not detected in plasma at any time post-treatment and ABZSO and ABZSO2 were the metabolites detected in plasma. Both metabolites were rapidly depleted from the bloodstream. ABZ and its metabolites were recovered in abomasal fluid from 0.25 up to either 48 (ABZ) or 120h (ABZSO and ABZSO2) post-treatment. 4. The plasma disposition kinetics of both ABZ metabolites was significantly changed in the feed-restricted compared with control calf. ABZSO and ABZSO2 plasma area under the curves (AUCs) were significantly higher in the restricted animal. These enhanced AUCs correlated with significantly longer plasma half-lives (T1/2el) and mean residence times (MRTs) for these metabolites. 5. The delayed elimination of ABZ metabolites from the bloodstream correlated with the higher concentration of these molecules recovered in the abomasal fluid of the calves subjected to a dietary restriction. 6. The changes observed on disposition kinetics may reflect an impairment on the hepatic metabolism and clearance of ABZ as a consequence of FFA mobilization from adipose tissue and overproduction of ketone bodies in the liver.

The influence of diet on the disposition kinetics of albendazole (ABZ) and its metabolites in pigs was investigated. ABZ was administered orally at 10 mg kg-1 to pigs fed either a commercially produced 35 per cent protein/grain concentrate diet (concentrate group), a whey-based diet supplemented with corn grain (whey/grain group) or grazed on pasture (pasture group). Blood samples were taken serially for 96 hours and plasma was analysed by high performance liquid chromatography (HPLC) for ABZ, ABZ sulphoxide (ABZSO), ABZ sulphone (ABZSO2) and amino-ABZSO2 (NH2ABZSO2). ABZ was not detected in plasma at any time after the treatment, and ABZSO and ABZSO2 were the main metabolites detected between 0.5 and 30 to 48 hours after treatment in all the experimental animals. Low concentrations of the NH2ABZSO2 metabolite were found in plasma between 18 and 36 hours after the administration of ABZ to all the groups of pigs. The pharmacokinetic behaviour of the ABZ metabolites in pigs fed either the concentrate of the whey/concentrate diet was substantially different from that observed in pigs grazing on pasture. The peak concentration (C(max)) and areas under the concentration-time curves (AUC) for ABZSO and ABZSO2 were significantly higher (P < 0.01) in the pigs fed on pasture, and were correlated with significantly longer elimination half-lives and mean residence times for both metabolites.

The comparative plasma disposition kinetics of albendazole (ABZ), fenbendazole (FBZ) and oxfendazole (OFZ) following their oral administration (5 mg/kg) to adult sheep was characterized. Jugular blood samples were taken serially over a 144 h period and plasma was analysed by high performance liquid chromatography (HPLC) for ABZ, ABZ sulphoxide (ABZSO) and ABZ sulphone (ABZSO2) (ABZ treatment), and for FBZ, OFZ and FBZ sulphone (FBZSO2) (FBZ and OFZ treatments). While the ABZ parent drug was not detected at any time post-treatment, ABZSO and ABZSO2 were the analytes recovered in plasma after oral administration of ABZ to sheep. The active ABZSO metabolite was the main analyte recovered in plasma (between 0.25 and 60 h post-treatment), accounting for 71% of the total AUC. FBZ, OFZ and FBZSO2 were the analytes detected in plasma following the oral administration of both FBZ and OFZ to sheep. Low concentrations of FBZ were found in plasma between 4 (FBZ treatment) or 8 h (OFZ treatment) and 72 h post-treatment. The plasma profile of each analyte followed a similar pattern after both treatments; OFZ being the main component detected in plasma. The plasma disposition of ABZ metabolites was markedly different to that of FBZ derivatives. ABZSO exhibited faster absorption and a higher Cmax than OFZ (both treatments). Furthermore, while ABZSO declined relatively rapidly in plasma reaching non-detectable concentrations at 60 h post-ABZ administration, OFZ was found in plasma for up to 120 (FBZ treatment) and 144 h (OFZ treatment).(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of methimazole on the plasma disposition kinetics of fenbendazole, oxfendazole and their metabolites, was investigated in adult sheep. The two anthelmintics were administered by oral drench at 5 mg kg-1 either alone (control treatments) or together with methimazole given orally at 3 mg kg-1. Blood samples were taken serially for 144 hours. Fenbendazole parent drug and its sulphoxide and sulphone metabolites were the three analytes observed by high performance liquid chromatography (HPLC) after the administration of both anthelmintics. The disposition of each analyte followed a similar pattern after the administration of the two anthelmintics alone. Oxfendazole was the main component recovered in plasma between four and 120 to 144 hours after the administration of both anthelmintics either with or without methimazole. A modified pattern of disposition, with significantly higher Cmax and AUC values for fenbendazole parent drug, and a delayed appearance in plasma with retarded Tmax values for the sulphoxide and sulphone metabolites, were the main pharmacokinetic changes observed when the drugs were administered with methimazole.

The purpose of this review article is to establish a relationship between pharmacological properties and clinical efficacy of the most widely used broad-spectrum veterinary anthelmintics. The impact of drug pharmacokinetics/pharmacodynamics on anthelmintic efficacy and resistance is discussed. We review the clinical pharmacokinetics of the currently available anthelmintics used in livestock-imidazothiazoles, tetrahydropyrimidines, benzimidazoles/pro-benzimidazoles, salicylanilides (closantel) and avermectin-type compounds. Understanding the pharmacokinetic and metabolic behaviour of broad-spectrum anthelmintics in the host, and factors modulating that behaviour, is highly important for maximizing anthelmintic utility and efficacy.