Influence of diet on the pattern of gastrointestinal biotransformation of netobimin and albendazole sulphoxide in sheep

Plasma concentrations of diclazuril following oral administration of diclazuril and diclazuril sodium salt to cattle

Diclazuril is a triazine-based antiprotozoal agent widely used in veterinary practice that may have clinical application in the treatment of bovine protozoal diseases. The present study reports on the bioavailability, pharmacokinetics, and metabolism of diclazuril and diclazuril sodium salt in cattle following administration of diclazuril suspended in water and by direct application of diclazuril sodium salt to the oral mucosa. Compared with diclazuril itself, the sodium salt formulation of diclazuril applied to the oral mucosa was rapidly and reliably absorbed. Plasma concentrations of diclazuril peaked at around 8 h after oral-mucosal administration of diclazuril sodium salt. On the contrary, application of diclazuril itself orally resulted in delayed and variable absorption. The mean bioavailability of diclazuril as pure powder was 42.5% relative to diclazuril sodium salt indicating approximately 2.5-fold increase in bioavailability of diclazuril as a sodium salt relative to diclazuril as a pure compound in cattle. The present study also reports finding of a previously unreported diclazuril metabolite at high concentrations in plasma especially after oral administration of diclazuril. Further studies, including synthesis and characterization of the novel described metabolite, are required to accurately determine aspects of the metabolism of diclazuril in cattle.

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.

Metabolic stability of glyphosate and its environmental metabolite (aminomethylphosphonic acid) in the ruminal content of cattle

Glyphosate (GLY) is one of the most commonly used herbicides worldwide. Both GLY and aminomethylphosphonic acid (AMPA), its main degradation product, may be present in feedstuffs offered to dairy cows. Although the major proportions of ingested GLY and AMPA are eliminated with faeces, a potential degradation of GLY to AMPA in the rumen of dairy cows has been suggested. Considering that the rumen plays a central role in the pre-systemic metabolism of xenobiotics, this research aimed to investigate whether or not GLY and AMPA are metabolised in the ruminal environment of cattle. The distribution of both compounds between the fluid and solid phases of the ruminal content (RC) was also evaluated. RC from 3 steers were collected in an abattoir. Aliquots were incubated (3-6 h) in anaerobiosis with GLY (15 µg/mL) and AMPA (1.5 µg/mL). Metabolic viability of RC was assessed by the measurement of the sulpho-reduction of the anthelmintic derivative albendazole sulphoxide (ABZSO) into albendazole (ABZ) in the absence (controls) or in presence of GLY and AMPA. Incubations of boiled (inactive) RC were used as controls. Samples were analysed by HLPC with fluorescence detection. Neither GLY nor AMPA were metabolised in metabolically active RC from cattle. Both compounds were predominantly found in the fluid phase compared to the solid (particulate) matter of RC. Neither GLY nor AMPA had a negative effect on the metabolic production of ABZ. A high metabolic stability of both compounds within the ruminal environment would be expected in vivo. Their presence in high proportion in the fluid phase of the ruminal content may give rise to a rapid flow of both GLY and AMPA to the posterior gastrointestinal tract. Negative effects on the ruminal biotransformation of therapeutically used drugs would not be expected when the herbicide and its degradation product are consumed with food.

Effects of feeding on the plasma disposition kinetics of the anthelmintic albendazole in laying hens

1. To optimise the use of albendazole (ABZ) as an anthelmintic in hens, the effects of fasting and type of diet on the plasma kinetics of ABZ and its metabolites were evaluated. 2. Twenty-four hens were distributed into 4 groups: In experiment I the Fed group were fed ad libitum, while the Fasted group was fasted over a 12-h period. In experiment II the Pelleted group was fed with pelleted commercial food, while the Grain group was fed with cereal grains. All the groups were treated with ABZ by oral route. Blood samples were taken and plasma analysed by HPLC. 3. ABZ and its metabolites albendazole-sulphoxide (ABZSO) and albendazole-sulphone (ABZSO2) were recovered in plasma in all the groups. The 12-h fasting period did not modify the disposition kinetics of ABZ in hens. The type of feed affected ABZ kinetics. ABZSO concentration profile was higher and detected for longer in the Grain group compared to the Pelleted group. Statistical differences were not found for AUC0-∞ values, whereas the T1/2for and T1/2el were different between groups. 4. Factors affecting ABZ kinetic behaviour should be taken into account to optimise its use to ensure the sustainability of the limited available anthelmintic therapeutic tools in avian parasite control.

Moxidectin and ivermectin metabolic stability in sheep ruminal and abomasal contents

The oral administration of macrocyclic lactones to sheep leads to poorer efficacy and shorter persistence of the antiparasitic activity compared to the subcutaneous treatment. Gastrointestinal biotransformation occurring after oral treatment to ruminant species has been considered as a possible cause of the differences observed between routes of administration. The current work was addressed to evaluate on a comparative basis the in vitro metabolism of moxidectin (MXD) and ivermectin (IVM) in sheep ruminal and abomasal contents. Both compounds were incubated under anaerobic conditions during 2, 6 and 24 h in ruminal and abomasal contents collected from untreated adult sheep. Drug concentrations were measured by high-performance liquid chromatography with fluorescence detection after sample clean up and solid phase extraction. Neither MXD nor IVM suffered metabolic conversion and/or chemical degradation after 24-h incubation in ruminal and abomasal contents collected from adult sheep. Unchanged MXD and IVM parent compounds represented between 95.5 and 100% of the total drug recovered in the ruminal and abomasal incubation mixtures compared with those measured in inactive control incubations. The partition of both molecules between the solid and fluid phases of both sheep digestive contents was assessed. MXD and IVM were extensively bound (>90%) to the solid material of both ruminal and abomasal contents collected from sheep fed on lucerne hay. The results reported here confirm the extensive degree of association to the solid digestive material and demonstrates a high chemical stability without evident metabolism and/or degradation for both MXD and IVM in ruminal and abomasal contents.

Effect of composition and quality of diet and feeding time on the kinetics and efficacy of some anthelmintic drugs: a mini-review

This article reviews the literature dealing with the effects of composition and quality of diet and feeding time on the pharmacokinetics and efficacy of some anthelmintic drugs in ruminants. Studies have suggested that greater availability, and therefore improved anthelmintic activity, is possible through temporary feed restriction. It is also recommended that anthelmintic drugs should not be given to animals whilst they are maintained on large feed intakes, particularly of lush pasture that promotes rapid gastric transit, as this may reduce drug availability and anthelmintic efficacy. Generally, feeding animals low-quality fibrous diets reduces the passage rate of digesta and allows more time for absorption of several anthelmintic drugs and their metabolites from the gut. Some kinetic data of drugs given to animals on such diets may be slightly different, but this does not necessarily indicate alteration of the dosages of the anthelmintic drug. Nonetheless, due consideration should be given to anthelmintic dosages under various dietary regimes if optimum efficacy is to be achieved at all times.

Effect of the ionophore antibiotic monensin on the ruminal biotransformation of benzimidazole anthelmintics

The benzimidazole (BZD) anthelmintics, netobimin (NTB) pro-drug and albendazole sulphoxide (ABZSO) are reduced to albendazole (ABZ) by ruminal microflora. The aim of the current work was to evaluate the influence of the ionophore monensin (MON) on the in vitro biotransformation of NTB and ABZSO by sheep ruminal fluid. Ruminal fluid, collected from Corriedale sheep, was preincubated (24 h) either without (control) or with known MON concentrations (0.5, 1.5 and 3.0 microg/mL) at 38 degrees C under a CO2 atmosphere. Afterwards, aliquots from both MON-pretreated and control ruminal fluid samples were incubated (30 and 60 min) with 2 microg/mL of either NTB or ABZSO. Incubated samples were chemically extracted and analysed by High Performance Liquid Chromatography to quantify the metabolites formed. The rate of ABZ production after 30 min of NTB incubation with control ruminal fluid was 0.023 microg/min. Conversely, the rates of ABZ formation were significantly (P<0.05) lower (0.009, 0.011 and 0.013 microg/min) when NTB was incubated with ruminal fluid pretreated with MON (at 0.5, 1.5 and 3.0 microg/mL, respectively). After both incubation periods, the reduction of ABZSO to ABZ was 22 to 70% lower when the ruminal fluid was preincubated with the different MON concentrations. The lower ABZ production observed in the presence of MON may result in a modified availability of this molecule in the gastrointestinal (GI) tract and hence, on its anthelmintic efficacy against GI nematodes.

In vitro ruminal biotransformation of benzimidazole sulphoxide anthelmintics: enantioselective sulphoreduction in sheep and cattle

The comparative in vitro sulphoreduction of the (+) and (-) enantiomers of albendazole sulphoxide (ABZSO) and oxfendazole (OFZ) by ruminal fluid obtained from sheep and cattle, was investigated, under anaerobic conditions, in this study. Ruminal fluid samples were obtained from Holstein steers fitted with a permanent rumen fistula and from Corriedale lambs via an oesophageal tube. Albendazole sulphoxide, incubated as either the racemic (rac) mixture or as each individual enantiomeric form, was extensively sulphoreduced to form albendazole (ABZ) by ruminal fluid from both species. The concentrations of ABZ formed at different incubation times were between 55 and 158% greater after the incubation of cattle ruminal fluid with (+) ABZSO, compared with that produced when (-) ABZSO was the incubated substrate. Similarly, the concentrations of ABZ were 1.3--3.0-fold higher when (+) ABZSO was incubated with sheep ruminal fluid. Significantly higher rates of depletion were observed for the (+) enantiomeric form when ABZSO was incubated with ruminal fluid from both species. The rates of ABZ formation from both ABZSO enantiomeric forms were significantly higher in sheep compared with cattle ruminal fluid. Fenbendazole (FBZ) was the metabolite formed after the incubation of the racemic form of OFZ with ruminal fluid obtained from both species. The metabolic profile of both OFZ enantiomers followed a similar pattern to that observed for ABZSO enantiomers. A bi-directional chiral inversion of one enantiomer into its antipode was observed. The (+) enantiomer appeared in the incubation medium when (-) ABZSO was the incubated substrate, and also the (-) antipode was detected after (+) ABZSO incubation with ruminal fluid obtained from both species. The results reported here demonstrate an enantioselective ruminal sulphoreduction of ABZSO and OFZ (substrate enantioselectivity). These findings contribute to interpret the chiral behaviour of benzimidazole-sulphoxide anthelmintics.