The pharmacology of flukicidal drugs

Plasma pharmacokinetics of clorsulon following administration of a single subcutaneous or intravenous injection to cattle

The benzenedisulfonamide derivative clorsulon is a potent fasciolicide which is marketed in fixed combination injectables, typically combined with the macrocyclic lactone ivermectin. In the presented pharmacokinetic study, the plasma profile of clorsulon in 32 healthy, young Brown Swiss cattle was administered a single intravenous dose at 3 mg/kg body weight or subcutaneously at 3, 6 or 12 mg/kg body weight (4 intact male and 4 female animals per treatment) as a 30% w/v clorsulon injection formulation. Serial blood samples were collected up to 24 days after administration to establish the pharmacokinetics, bioavailability and dose proportionality of clorsulon. Following a single intravenous injection of clorsulon at 3 mg/kg body weight, the area under the concentration versus time curve from the start of dose administration to the time of the last quantifiable concentration (AUClast ) was 4830 ± 941 day*ng/mL, and half-live was 2.37 ± 0.98 days. The back extrapolated concentration at time 0 was 38,500 ± 6070 ng/mL. The volume of distribution at steady state and clearance were 685 ± 107 mL/kg and 664 ± 127 mL/day/kg, respectively. In the groups dosed at 3, 6 or 12 mg/kg body weight by subcutaneous injection, clorsulon plasma concentrations rose to maximum within 0.5 day and decreased to the last sample point. For these groups, the maximum plasma clorsulon concentrations were 3100 ± 838, 5250 ± 1220 and 10,800 ± 1730 ng/mL, respectively, and the AUClast was 5330 ± 925, 9630 ± 1300 and 21,500 ± 3320 day*ng/mL, respectively. Half-lives, 2.01 ± 0.62, 3.84 ± 1.42 and 5.36 ± 0.60 days, respectively, increased significantly with dose, likely related to increasing dose volume. Clorsulon was well absorbed and fully bioavailable (103%-114%) after subcutaneous injection. No gender-related difference in systemic exposure was observed. Assessment of Cmax and AUClast demonstrated a proportional increase in systemic exposure to the clorsulon subcutaneous doses over the range of 3-12 mg/kg body weight.

Oksfendazol, oksiklozanid ve oksfendazol-oksiklozanid kombinasyonunun koyun ve keçilerde biyokimyasal ve hematolojik parametreler üzerine etkileri

Mevcut araştırmada sağlıklı koyun ve keçilere oral yolla oksfendazol, oksiklozanid ve oksfendazol-oksiklozanid kombinasyon uygulamasının, farklı zamanlarda biyokimyasal ve hematolojik parametreler üzerine etkisinin belirlenmesi amaçlandı. Çalışma çapraz dizaynda 6 adet sağlıklı dişi, 1-3 yaştaki İvesi koyun ve Alpin keçi üzerinde gerçekleştirildi. Koyun ve keçilere oral yolla 7.5 mg/kg oksfendazol, 15 mg/kg oksiklozanid ve oksfendazol-oksiklozanid (7.5 mg/kg-15 mg/kg) kombinasyonu uygulandı. Kan örnekleri ilaç uygulamalarından önce (0.saat, kontrol) ve sonraki 8., 24., 72. saat ile 7. günde alındı. Biyokimyasal parametrelerden albümin, alkalen fosfataz, alanin aminotransferaz, aspartat aminotransferaz, kolesterol, trigliserid, total protein, kan üre nitrojen, kreatinin değerleri otoanalizatör cihazında belirlendi. Hematolojik parametrelerden alyuvar sayısı, hemoglobin, hematokrit, ortalama korpüsküler hacim, ortalama korpüsküler hemoglobin, ortalama korpüsküler hemoglobin konsantrasyonu, akyuvar sayısı, lenfosit, monosit, % granülosit, % lenfosit, % monosit ve % eritrosit dağılım genişliği değerleri kan hücresi sayım cihazında ölçüldü. İlaç grupları ve zamana bağlı olarak hematolojik ve serum biyokimya parametrelerinde anlamlı bir fark bulunamadı. Bu sonuçlar koyun ve keçilere oral yolla, 7.5 mg/kg oksfendazol ve 15 mg/kg oksiklozanid tek veya kombine olarak uygulandığında hematolojik ve biyokimyasal parametrelerin fizyolojik sınırlarda olduğu ve klinik olarak anlamlı bir etkisinin olmadığını göstermektedir.

The Pattern of Blood-Milk Exchange for Antiparasitic Drugs in Dairy Ruminants

Simple Summary

This review article is focused on the description of the plasma–milk partition coefficients for different antiparasitic drug classes in dairy ruminants, and it contributes to rational pharmaco-therapy in lactating dairy animals, which is critical to understand the pattern of drug excretion in milk as well as the residual concentration patterns in dairy products elaborated by processing milk from drug-treated animals.

Abstract

The prolonged persistence of milk residual concentration of different antiparasitic drugs in lactating dairy animals should be considered before recommending their use (label or extra-label) for parasite control in dairy animals. The partition blood-to-milk ratio for different antiparasitic compounds depends on their ability to diffuse across the mammary gland epithelium. The high lipophilicity of some of the most widely used antiparasitic drugs explains their high partition into milk and the extended persistence of high residual concentrations in milk after treatment. Most of the antiparasitic drug compounds studied were shown to be stable in various milk-related industrial processes. Thus, the levels of residues detected in raw milk can be directly applicable to estimating consumer exposure and dietary intake calculations when consuming heat-processed fluid milk. However, after milk is processed to obtain milk products such as cheese, yogurt, ricotta, and butter, the residues of lipophilic antiparasitic drugs are higher than those measured in the milk used for their elaboration. This review article contributes pharmacokinetics-based information, which is useful to understand the relevance of rational drug-based parasite control in lactating dairy ruminants to avoid undesirable consequences of residual drug concentrations in milk and derived products intended for human consumption.

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.

Understanding the main route of drug entry in adult Fasciola hepatica: Further insights into closantel pharmacological activity

Closantel (CLS) is highly effective against adult liver flukes after its oral or subcutaneous (sc) administration in ruminants. Trans-tegumental diffusion and oral ingestion are the two potential routes available for the entry of drugs into Fasciola hepatica. The work reported here contributes to improve the understanding of CLS pharmacology. The main goals of were: I) to determine the pattern of in vivo CLS accumulation into adult F. hepatica and relevant tissues in CLS-treated sheep; II) to investigate the influence of the physicochemical composition of the incubation medium on the CLS diffusion process into adult F. hepatica; III) to assess the ovicidal activity of CLS against F. hepatica eggs; and IV) to investigate the in vivo effect of CLS treatment on glutathione S-transferases activity in adult liver flukes exposed to CLS. Fourteen healthy sheep were each orally infected with 75 F. hepatica metacercariae. Sixteen (16) weeks after infection, animals were treated with CLS by oral (n = 6, 10 mg/kg) or sub-cutaneous (sc) (n = 6, 5 mg/kg) route. At 12, 24 and 36 h post-treatment, animals were sacrificed (n = 2) and samples of blood, bile and adult F. hepatica were collected. In addition, flukes recovered from non-treated sheep (n = 2) were ex vivo incubated (60 min) in the presence of CLS in either RPMI or bile as incubation medium. CLS concentration was measured by HPLC. The ovicidal activity of CLS was investigated using eggs obtained from the bile of untreated sheep. Finally, glutathione S-transferase activity in F. hepatica recovered from untreated and CLS-treated sheep was assessed. In the in vivo studies, the highest CLS concentrations were measured in plasma and adult liver flukes. A positive correlation was observed between CLS concentration in plasma and in F. hepatica. Results obtained in the current work indicate that the in vivo accumulation of CLS into adult liver flukes occurs mainly by the oral route. After ex vivo incubation, the uptake of CLS by the parasite was markedly diminished in the presence of bile compared with that observed in the presence of RPMI as incubation medium. CLS lacks ovicidal activity at therapeutically relevant concentrations. Lastly, CLS significantly increased glutathione S-transferase activity in flukes recovered at 12 h (oral treatment) and 24 h (sc treatment), compared to the control liver flukes.

Molecular and immunological characterization of Fasciola antigens recognized by the MM3 monoclonal antibody

Fascioliasis is a re-emerging parasitosis produced by liver flukes of the genus Fasciola. In this study we used protein fingerprinting (PMF) and MS/MS analysis to investigate the Fasciola secretory antigens that are recognized by mAb MM3. The results showed that mAb MM3 binds to several Fasciola cathepsins L1 and L2, but also co-purifies a Kunitz-type protein previously described in F. hepatica, which appears to bind to Fasciola cathepsins L. After identifying the target antigens for mAb MM3, we cloned and expressed a cathepsin L1 isoform in E. coli (gb|FR848428), which after refolding exhibited the MM3-recognized epitope and displayed cysteine protease activity. Using native, folded-recombinant and denatured-recombinant Fasciola cathepsins L as targets, we demonstrated that during F. hepatica infections in sheep, antibody responses to linear and conformational epitopes present on cathepsins L are promoted. However, the antibody response to linear epitopes was only detected in significant amounts in animals suffering from repeated infections. A different antibody response to linear and conformational epitopes also appears to occur in rabbits immunized with native or recombinant unfolded cathepsins, as sera from animals immunized with the latter did not react with native cathepsins and vice versa. In addition, the ELISA inhibitions showed that the MM3 epitope is not recognized by rabbits, which explains the usefulness of these species for producing capture antibodies for use in MM3-ELISA assays.

Evaluation of the flukicide treatment policy for dairy cattle in Galicia (NW Spain)

Fasciola hepatica infection is an important cause of lost productivity in livestock worldwide. Effective control of fasciolosis is difficult, especially in milking cows, which can only be treated during dry periods, a control strategy that has not been yet evaluated. In this cross-sectional study, we investigated the effect of the type of flukicide treatment on the prevalence and intensity of infection in dairy cattle from Galicia, an area where fasciolosis is endemic and which is also the main milk-producing region in Spain. Faecal samples were taken from 5188 dairy cows on 275 randomly selected farms for measurement of the concentration of F. hepatica coproantigens by a monoclonal antibody based immunoassay (MM3-COPRO ELISA). On the same day as the sampling, each farm owner/manager was questioned about the types of treatment used on the farm. Three groups of farms were considered according to the fasciolicide treatment: (A) flukicides were not used, (B) an anthelmintic effective against mature stages of flukes was used (albendazole or netobimin) and (C) a fasciolicide effective against immature and mature stages was used (triclabendazole: TCBZ). Results indicated that 16.0% (832/5188) cows from 61.1% (168/275) herds were infected by F. hepatica. The mean coproantigen concentration in infected herds was 13.0ng/ml (range 0.9-112.6ng/ml). The highest individual concentration recorded was 496.6ng/ml. Herd and within-herd prevalences of F. hepatica were similar in all three groups, but surprisingly, individual prevalence and antigen concentration were higher in Group C (p<0.05). The percentage of farms with within-herd prevalences >25% was very high in all three groups, and no significant differences were observed. In contrast, the percentage of herds with mean antigen concentrations >20ng/ml was significantly lower (p<0.05) in Groups A and B (14.4% and 14.9%, respectively) than in Group C (50.0%). The proportion of herds that exceeded both limits (25% for prevalence and/or 20ng/ml for coproantigen concentration) was also significantly higher (p<0.05) in Group C than in untreated animals (Group A). The survey showed that most dairy farmers are unaware of the existence of F. hepatica infection on their farms, and treatments, when given, are administered without prior diagnosis. Treatment with TCBZ administered only at drying off did not show advantages over other measures including no treatment, or treatment with other benzimidazoles. Consequently, TCBZ should only be used to treat individual animals after correct diagnosis of the infection, and correct management measures taken to control re-infection.

Triclabendazole for the treatment of fascioliasis and paragonimiasis

Fascioliasis and paragonimiasis, which are caused by liver flukes (Fasciola) and lung flukes (Paragonimus), are emerging public health problems. Several hundred millions of people are at risk of the two diseases that cause considerable morbidity and delay socio-economic development. Triclabendazole, a benzimidazole derivative, has been routinely used since 1983 in veterinary medicine to control infections with Fasciola spp. in domestic herbivorous animals. In 1986, a veterinary formulation of triclabendazole was first administered to two human patients with fascioliasis. Clinical data obtained thus far suggest that triclabendazole is the most efficacious and best tolerated drug for the treatment of fascioliasis. Moreover, the drug holds promise as a useful therapeutic alternative to praziquantel in the treatment of paragonimiasis. This review of triclabendazole includes an overview of the pharmacodynamics and pharmacokinetics, toxicology and efficacy against the major food-borne trematodes in laboratory animals. Data from case reports and clinical trials in humans infected with Fasciola spp. and Paragonimus spp. are summarised and the current state of triclabendazole regarding treatment of human fascioliasis and paragonimiasis is described. Efforts to facilitate broader registration of this drug should go hand-in-hand with research and development on novel drugs against food-borne trematodiasis, better access to improved sanitation, sound health education and the development of new technologies for assuring food safety.

Tomocomd-Cardd, a novel approach for computer-aided ? rational? drug design: I. Theoretical and experimental assessment of a promising method for computational screening and in silico design of new anthelmintic compounds

In this work, the TOMOCOMD-CARDD approach has been applied to estimate the anthelmintic activity. Total and local (both atom and atom-type) quadratic indices and linear discriminant analysis were used to obtain a quantitative model that discriminates between anthelmintic and non-anthelmintic drug-like compounds. The obtained model correctly classified 90.37% of compounds in the training set. External validation processes to assess the robustness and predictive power of the obtained model were carried out. The QSAR model correctly classified 88.18% of compounds in this external prediction set. A second model was performed to outline some conclusions about the possible modes of action of anthelmintic drugs. This model permits the correct classification of 94.52% of compounds in the training set, and 80.00% of good global classification in the external prediction set. After that, the developed model was used in virtual in silico screening and several compounds from the Merck Index, Negwer's handbook and Goodman and Gilman were identified by models as anthelmintic. Finally, the experimental assay of one organic chemical (G-1) by an in vivo test coincides fairly well (100%) with model predictions. These results suggest that the proposed method will be a good tool for studying the biological properties of drug candidates during the early state of the drug-development process.

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.

The comparative metabolism of triclabendazole sulphoxide by triclabendazole-susceptible and triclabendazole-resistant Fasciola hepatica

Benzimidazole anthelmintics are widely used against nematode, cestode and trematode parasites. The drugs undergo several enzyme-mediated reactions within the host animal that produce a number of metabolites. Although it has been shown that certain helminths, including Fasciola hepatica, can metabolise albendazole, nothing is known regarding the ability of the liver fluke to metabolise triclabendazole, which is the major flukicidal compound currently on the market. In the current study, adult triclabendazole-susceptible flukes were treated with triclabendazole sulphoxide in vitro, and the metabolism of the drug was monitored by high performance liquid chromatography. The data show that F. hepatica can metabolise triclabendazole sulphoxide into its relatively inert sulphone metabolite. Parallel experiments using triclabendazole-resistant flukes showed that the conversion of triclabendazole sulphoxide to triclabendazole sulphone was on average 20.29% greater in the resistant flukes compared with the susceptible flukes. The results are discussed with regard to the mechanism of triclabendazole resistance in F. hepatica.

The binding of closantel to ovine serum albumin, and homogenate fractions of Haemonchus contortus

Closantel binds to the serum proteins of the host and affects blood sucking parasites when they ingest the blood of treated hosts. Closantel binds specifically to ovine serum albumin (K(a) of 9. 3x10(6)M(-1)) at site I, the warfarin/phenylbutazone binding site of albumin Closantel also binds to invertebrate haemocyanin and haemolymph. The strongest binding of closantel in homogenates of H. contortus is found in fractions containing soluble proteins. This binding is of low affinity and, because the site itself is not fully denaturable, it may not be proteinaceous. There is no detectable difference in binding affinity between homogenate fractions from closantel susceptible and resistant isolates of adult or larval worms suggesting that closantel resistance is not due to changes in the closantel receptor or carrier.

Fasciolicides: efficacy, actions, resistance and its management

The modes of action of fasciolicides are described. Closantel and other salicylanilides interfere with energy metabolism by uncoupling oxidative phosphorylation in the fluke. Other fasciolicides are believed to have a metabolic action-halogenated phenols (via uncoupling) and clorsulon (via inhibition of glycolysis)-but direct evidence is lacking. Benzimidazoles (in particular, triclabendazole) bind to fluke tubulin and disrupt microtubule-based processes. Diamphenethide inhibits protein synthesis in the fluke. Other potential drug actions may contribute to overall drug efficacy. In particular, a number of fasciolicides-salicylanilides, phenols, diamphenethide-induce a rapid paralysis of the fluke, so their action may have a neuromuscular basis, although the actions remain ill-defined. Resistance to salicylanilides and triclabendazole has been detected in the field, although drug resistance does not appear to be a major problem yet. Strategies to minimize the development of resistance include the use of synergistic drug combinations, together with the design of integrated management programmes and the search for alternatives to drugs, in particular, vaccines.

Comparative anthelmintic activity of strategic sustained low-level administration of albendazole in feed pellets compared to single doses of closantel and tetramisole against natural ovine parasitic gastroenteritis

The strategic use of single therapeutic doses of closantel, tetramisole or sustained low-level administration of albendazole in feed pellets in controlling naturally acquired parasitic gastroenteritis in sheep was investigated on a farm in semi-arid Rajasthan, India. A total of 303 5- to 6-month-old sheep were divided into three groups. Two groups were dosed with single therapeutic doses of closantel and tetramisole and the third group was given a low-level medication with albendazole through feed pellets for 30 days. Faecal egg counts revealed significantly lower counts (p<0.001) in the group treated with closantel compared to the other two groups. The faecal egg counts in the group receiving sustained low-level albendazole rose after withdrawal of the medication but remained significantly lower than those in the group treated with tetramisole up to 7 weeks after treatment (p<0.05). On the other hand, in the group treated with tetramisole, the mean faecal egg count rose from 3 weeks after treatment and remained continuously higher than those in any other group up to 12 weeks after treatment. The closantel-treated group gained more body weight but the first six-monthly greasy fleece yield was greater in the group treated with medicated pellets. During the first 3 months of the experiment, three animals in the group treated with tetramisole died of parasitic gastroenteritis. Following sustained low-level administration of albendazole in feed pellets, the plasma disposition curve of both the sulphoxide and sulphone metabolites reached its plateau level by day 5 and remained almost constant thereafter. The comparative cost-effectiveness of the three treatment regimes during the first 3 months of treatment was best for the group treated with closantel followed by the group treated with medicated feed pellets.

Modes of action of anthelmintic drugs

Modes of action of anthelmintic drugs are described. Some anthelmintic drugs act rapidly and selectively on neuromuscular transmission of nematodes. Levamisole, pyrantel and morantel are agonists at nicotinic acetylcholine receptors of nematode muscle and cause spastic paralysis. Dichlorvos and haloxon are organophosphorus cholinesterase antagonists. Piperazine is a GABA (gamma-amino-butyric acid) agonist at receptors on nematode muscles and causes flaccid paralysis. The avermectins increase the opening of glutamate-gated chloride (GluCl) channels and produce paralysis of pharyngeal pumping. Praziquantel has a selective effect on the tegument of trematodes and increases permeability of calcium. Other anthelmintics have a biochemical mode of action. The benzimidazole drugs bind selectively to beta-tubulin of nematodes, cestodes and fluke, and inhibit microtubule formation. The salicylanilides: rafoxanide, oxyclozanide, brotianide and closantel and the substituted phenol, nitroxynil, are proton ionophores. Clorsulon is a selective antagonist of fluke phosphoglycerate kinase and mutase. Diethylcarbamazine blocks host, and possibly parasite, enzymes involved in arachidonic acid metabolism, and enhances the innate, nonspecific immune system.

Haemonchus contortus: the uptake and metabolism of closantel

Closantel is an anthelmintic which associates with plasma albumin and is useful for the control of sheep parasites, such as Haemonchus contortus, that ingest blood. However, the utility of closantel for parasite control has been threatened by the emergence of resistance. The mechanisms of resistance are unknown. A closantel-resistant and a closantel-susceptible isolate of H. contortus were compared with respect to the distribution and metabolism of closantel. Neither strain appeared to metabolise closantel in vitro or in vivo. Following treatment of infected sheep with radioactively labelled closantel, isotope levels in closantel-resistant adult H. contortus were significantly lower than in susceptible worms. This reduced accumulation of drug could contribute to closantel resistance by mechanisms such as reduced feeding, failure to dissociate the drug-albumin complex in the gut or increased efflux of closantel from resistant worms.

The disposition of antiparasitic drugs in relation to the development of resistance by parasites of livestock

The kinetic and dynamic disposition of endo- and ectoparasiticides in livestock in relation to development of resistance is examined. Based on the modes of action of antiparasitic drugs, maximum activity necessitates that the parasite be exposed to 'toxic' concentrations for as great a duration as possible. In contrast, exposure to non-lethal discriminating drug concentrations has a significant potential to promote the development of resistance. Orally administered anthelmintics quickly associate with particulate digesta in the rumen; their subsequent desorption from particulate matter as it vacates the rumen maintains the duration of metabolite availability. The flow rate of digesta increases with feed intake and the presence of gastrointestinal parasites, and together with other parasite-induced physiological changes to the gut, contributes to reduced duration of drug availability. The potential for orally administered drugs to bypass the rumen, due to closure of the oesophageal groove, exacerbates the effect. Once absorbed, the metabolite concentration with time profile progressively decreases, the rate depending upon the chemical nature of the drug and the type and condition of the host into which it was administered. The greater hepatic activity of goats speeds drug elimination, the lower dose equivalent availability increases the potential for generation of drug resistance in parasites of goats as compared to sheep. Parasites whose resistance is generated in goats may be then transferred to sheep. Similar distribution/elimination kinetics apply to topically administered insecticides of sheep. The progressively reducing concentrations expose ectoparasites to discriminating drug levels, again contributing to the development of resistance. It is anticipated that a greater understanding of the physiological/pharmacological effects which are described in this review will permit the more efficient use of existing and future antiparasitic drugs.

Effect of early treatment with rafoxanide on antipyrine clearance in sheep infected with Fasciola hepatica

1. The effect of the salicylanilide compound rafoxanide against immature stages of Fasciola hepatica was investigated in sheep using a series of antipyrine clearance tests and measuring glutamate dehydrogenase and gamma-glutamyl transferase activities in plasma. 2. Three animal groups were used. In two groups, sheep were infected with 200 metacercariae each. Four weeks after infection one of the two groups was treated with rafoxanide and the other was left untreated. The third group was unparasitized and also received rafoxanide. 3. Infection was confirmed by post-mortem examination of the livers of infected sheep. Infection did not alter the plasma disposition of rafoxanide. 4. The efficacy of rafoxanide, as assessed by the reduction in the number of adult flukes in treated animals compared with controls, was 85%. 5. Glutamate dehydrogenase activity fell dramatically 2 weeks after treatment but increased again at 12 weeks post-infection in the infected rafoxanide-treated group. 6. Antipyrine clearance decreased between 8 and 14 weeks post-infection in untreated sheep. In the infected rafoxanide-treated group plasma clearance of antipyrine remained unchanged until 10 weeks after rafoxanide administration when it decreased from the preinfection value of 5.09 to 3.90 ml.kg/min. Rafoxanide did not affect antipyrine disposition in uninfected sheep. 7. It was concluded that rafoxanide had an incomplete anthelmintic effect against immature stages of Fasciola hepatica, and that surviving parasites caused delayed liver damage which was reflected in an elevation in glutamate dehydrogenase activity and decreased plasma clearance of antipyrine.

Effects of dietary variations on plasma concentrations of oral flukicides in sheep

Groups of parasite-free lambs which were either housed and fed hay and concentrates or were grazing on pasture were dosed with the oral flukicides rafoxanide and triclabendazole and subsequent plasma concentrations monitored. Peak plasma concentrations and areas under curves (AUC) of both chemicals were significantly reduced in the grazing compared with the housed lambs. In order to investigate the observation similar groups of lambs were dosed orally with chromium EDTA and faecal throughput estimated. It was observed that the rate of throughput was greater in the grazing lambs, leading to the conclusion that the differences in plasma concentrations of the flukicides was caused by a reduction in their absorption in the grazing lambs. The implications on flukicide efficacy and dose rates are discussed.