ABSTR ACTan early switch to SID.During the development program and since approval, pharmacokinetic data was in collected in PK, efficacy and higher dose margin of safety studies.The data was used to build a population pharmacokinetic (popPK) model and simulate PK profiles following four different dose scenarios.The dataset contained

Infection of sheep by gastrointestinal nematodes (GIN) in pastoral systems such as those found in the South Western area of France, the Pyrénées Atlantiques , is one of the main reasons for economic loss and degradation of their welfare. In the present study, the efficacy of eprinomectin (EPN) was monitored on farms from this area following suspicion of lack of anthelmintic efficacy. Suspicions were raised by veterinarians, based on clinical signs ranging from milk and body condition loss, to anaemia, and mortality. Resistance was evaluated according to the World Association for the Advancement for Veterinary Parasitology (WAAVP) guidelines using fecal egg count reduction tests reinforced by individual analysis of drug concentration in the serum of all treated ewes by high-performance liquid chromatography (HPLC). EPN was administered by subcutaneous (SC) and topical (T) route according to manufacturer's requirements, as well as by the oral route (O) with the topical solution according to off-labelled practices in the field. For the first time in France, the presence of resistant isolates of Haemonchus contortus to EPN was observed in 5 dairy sheep farms. The HPLC dosages showed exposure of worms to concentrations compatible with anthelmintic activity for animals treated by the SC and O routes. By contrast, they showed under exposure to the drug of most individuals treated by the T route. EPN is the only null milk withdrawal anthelmintic molecule currently available. The presence of resistant isolates of the pathogenic H. contortus to EPN in this important dairy region requires an urgent change in grazing, and sometimes production, systems.

Malgré leur excellente activité anti-parasitaire, il est possible que l’ivermectine (IVM) et désormais la moxidectine (MOX) - toutes deux de la famille des lactones macrocycliques - soient utilisées de manière suboptimale dans la gale. Une meilleure connaissance de leur distribution dans la peau, et notamment dans le stratum corneum (SC) devrait permettre une optimisation de leur utilisation chez l’Homme. Une étude de 2002 réalisée chez 5 patients trouvait des concentrations d’IVM à la surface cutanée plus importantes dans les zones séborrhéiques et suggérait que la diffusion cutanée optimale de l’IVM passait par le manuportage du sébum. L’objectif de notre étude était d’évaluer la pharmacocinétique (PK) cutanée de la MOX et de l’IVM dans un modèle expérimental porcin de gale développé à l’École nationale vétérinaire d’Alfort. Quatre porcs ont reçu simultanément de la MOX (0,3 mg/kg à j0) et de l’IVM (0,2 mg/kg à j0 et j8) par voie orale. Des prélèvements plasmatiques, cutanés (par biopsies) et de SC (recueillis selon une méthode non invasive par des disques adhésifs) ont été effectués jusqu’à 11 jours après administration des 2 molécules. La quantification du SC a été réalisée par trois méthodes : poids des squames, dosage du cholestérol et échelle visuelle. La MOX et l’IVM ont été dosées par chromatographie liquide à haute performance (Inra, Toulouse). Dans le plasma on trouvait un pic à H6 puis une décroissance pour la MOX et l’IVM. Les profils PK de la MOX dans la peau et le SC étaient comparables avec un pic à j1 puis une décroissance lente. Les valeurs cutanées dosées par les deux techniques étaient positivement corrélées. Dans la peau, l’IVM présentait une cinétique comparable à la MOX mais avec des concentrations inférieures. Sa distribution dans le SC était différente avec un plateau obtenu à partir de j2. Le dosage du cholestérol et l’échelle visuelle apparaissaient comme les meilleures techniques pour quantifier le SC (Fig. 1 et 2). Les dosages de MOX dans les prélèvements non-invasifs de SC (par disques adhésifs) semblent être un bon reflet des concentrations cutanées dans le modèle animal. L’IVM semble avoir un profil de distribution différent dans le SC, similaire à celui décrit par Haas et al. Cette différence pourrait s’expliquer par une différence de concentration dans le sébum, la sueur ou de leur liaison à la kératine. Les profils de distribution de la MOX et de l’IVM dans le SC, le lieu de vie des sarcoptes, apparaissent différents. La technique de prélèvement par disques adhésifs pourrait être développée chez l’Homme. Une étude évaluant la corrélation entre la diffusion cutanée des lactones macrocycliques et leur succès/échec dans la gale sera à faire.

Resistance to ivermectin and moxidectin was explored by a faecal egg count reduction test in two sheep flocks with suspected anthelmintic resistance. The FECRT confirmed one suspicion, with a mean percentage of reduction in egg excretion within the treated groups of 0% for ivermectin (CI 95%: -228 to 58) and 13% for moxidectin (CI 95%: -152 to 70). This was further explored by a controlled efficacy test. An experimental infection of 18 naïve lambs was set up using infective larvae isolated from this flock (5000 L3/lamb). Compared to the control group, abomasal worm burdens (Teladorsagia circumcincta) were reduced by 90% [CI 95%: 81.5-94.8] and 85% [CI 95%: 72.4-92.2] after ivermectin (p<0.05) and moxidectin (p<0.05) treatment respectively. Again, compared to the control group, there was a reduction for intestinal strongyles (Trichostrongylus colubriformis) of 100% and 99% [CI 95%: 97.5-99.7] for ivermectin and moxidectin respectively. No difference was found between the efficacy of moxidectin and ivermectin. Pharmacokinetic values indicated that the strongyles were submitted to anthelmintic concentrations usually lethal to them. This trial demonstrated the first multiple resistance of ovine strongyles in France.

Les thérapeutiques dans la gale humaine restent encore limitées. L’ivermectine (IVM) a une efficacité documentée mais pas absolue, une demi-vie plasmatique relativement courte et une absence d’ovicidie, d’où un couplage fréquent aux topiques anti-scabieux et une 2e prise nécessaire entre j7 et j14 (hors AMM). L’afoxolaner (AFX), de la famille des isoxazolines, administrée oralement, de découverte récente en médecine vétérinaire, pourrait présenter un intérêt pour l’homme. L’objectif de l’étude était de comparer l’efficacité de l’AFX et de l’IVM dans un modèle animal de gale porcine. À l’École nationale vétérinaire d’Alfort, des porcs ont été expérimentalement infestés par S. scabiei var. suis, aprés avis éthique. À S9 post-infestation, 12 porcs ont été répartis de manière aléatoire en 3 groupes et traités à l’insu des observateurs. Le 1er groupe a reçu de l’IVM orale (Stromectol®) à la dose de 0,2 mg/kg à j0 et j8 ; le 2e de l’AFX oral (Nexgard®) à la dose de 2,5 mg/kg à j0, et le 3e groupe était non traité (témoin). Pour suivre l’infestation, un score clinique et un score de prurit ont été utilisés. Les sarcoptes observés dans des raclages ont été comptés. Des œufs prélevés après traitement ont été incubés et observés. Le critère de jugement principal était l’absence de sarcoptes à j14 post-traitement. Le financement était assuré par une subvention de la SFD. À j14, le pourcentage de réduction du nombre de sarcoptes était respectivement de 100 % et 96 % dans les groupes AFX et IVM. Quatre sur 4 des porcs du groupe AFX vs 2/3 du groupe IVM n’avaient plus de sarcoptes alors que les contrôles restaient infestés. Un porc du groupe IVM est décédé à S10 (malformation congénitale). Les scores cliniques et de prurit avaient diminué pour les porcs des 2 groupes traités (pas de différence significative) alors qu’ils restaient élevés chez les témoins. Tous les œufs incubés ont été capables d’éclore. Les résultats montrent l’absence de sarcoptes à j14 chez les porcs traités par une seule dose d’AFX et la présence d’un faible nombre de parasites chez 2/3 des porcs traités par 2 doses d’IVM. L’AFX a obtenu l’AMM pour le traitement des tiques et des puces du chien en 2014. Il agit sur les récepteurs des canaux chlore régis par le GABA, différents de ceux déjà connus et identifiés pour les lactones macrocycliques. Cette molécule lipophile a une absorption rapide, avec un pic en 2 à 4 heures (vs 4 à 6 heures pour l’IVM) et sa demi-vie plasmatique est longue (15,2 ± 5,1 jours vs 12 à 56 heures pour l’IVM). L’AFX, actuellement uniquement autorisée pour un usage vétérinaire, pourrait présenter une alternative thérapeutique pour la gale chez l’homme, notamment en cas d’échec ou de résistance aux lactones macrocycliques ou aux pyrèthres. La possible meilleure efficacité pourrait être liée aux propriétés pharmacologiques (i.e. plus grande rémanence cutanée).

Preliminary data suggest that topical eprinomectin in goat shows an individual variation in anthelmintic efficacy when used off-license at a dose rate of 0.5 or 1.0mg/kg BW. As a result, the use of oral administration of topical formulation of eprinomectin tends to develop in dairy goat farms in France. The plasma levels and milk excretion as well as the anthelmintic efficacy of eprinomectin were determined in goats following oral administration of a topical formulation of the drug at dose rates of 0.5 and 1mg/kg BW. The area under the concentration-time curve (AUC) values were 17.62 ± 9.68 ng day/ml and 6.56 ± 4.00 ng day/ml for plasma and milk respectively after the administration of 0.5mg/kg BW and 45.32 ± 13.90 ng day/ml and 13.88 ± 1.77 ng day/ml for plasma and milk, respectively after the administration of 1mg/kg BW. The milk-to-plasma ratio ranged from 0.33 to 0.36 and the amount of drug recovered in the milk was 0.4% of the total administered dose. The maximum concentrations of eprinomectin residues determined in milk after oral treatment were < 20 μg/kg (Maximum Residue Limit in goat milk). The anthelmintic efficacy of the oral administration of topical eprinomectin was 100% through Faecal Egg Count Reduction Test in natural infection and ≥ 99.8% through Controlled Test in experimental infection (Haemonchus contortus and Trichostrongylus colubriformis). Additional information is needed about the fate of the vehicles used for topical formulation when given by oral route concerning food safety.

Non-specific mechanisms involving ATP-binding cassette drug efflux transporters may play an important role in xenobiotic clearance in ovine gastro-intestinal nematodes. By using transporter inhibitors, the aim of this trial was to assess the possibility of increasing drug bioavailability in the host in an attempt to improve treatment efficacy. Thirty-six lambs were infected with 5000 multiple-drug resistant Haemonchus contortus third stage larvae and separated into six groups (n=6): ivermectin alone (IVM; 0.2mg/kg body-weight, BW), ketoconazole alone (KET; 10mg/kg BW), Pluronic 85 alone (P85; 4mg/kg BW), IVM+KET, IVM+P85 or untreated control. Ivermectin was administered once on day 28 post-infection for all appropriate groups, whereas KET and P85 were administered as five separate doses on day 26–30 post-infection inclusive. The resultant data showed that concomitant administration of KET or P85 with IVM induced increases in plasma and tissue concentrations of IVM in treated animals, resulting in a two-fold increase in the area under the time–concentration curve (p<0.05). Faecal egg counts and worm burdens of the IVM+KET and IVM+P85 groups were lower than in the untreated, KET and P85 alone control animals. Worm burdens were reduced by between 16% and 51% with IVM+KET and IVM+P85 respectively compared to untreated control animals. The co-administration of P85 with IVM increased the efficacy by 34%, compared with IVM alone, in terms of worm count reduction of the multi-resistant isolate of H. contortus.

The anthelmintic sensitivity of two field-derived isolates (designated FI001 and FI004) of cattle nematodes from beef farms in Scotland were investigated in a controlled efficacy test (CET). Efficacies of ivermectin pour-on (IVM-PO), IVM injectable (IVM-INJ) and moxidectin pour-on (MOX-PO) formulations were assessed. In each group, five helminth-naïve calves were infected experimentally with 50,000 third stage larvae from either isolate and administered with anthelmintic at the manufacturers' recommended dose rate 28 days later. For each isolate, nematode burdens were compared between treatment and control groups to determine efficacy. Nematode species composition, based on data derived from the untreated control groups' burden estimations, were 39 and 14% Cooperia oncophora and 61 and 86% Ostertagia ostertagi for isolates FI001 and FI004, respectively. Macrocyclic lactone resistance in C. oncophora was confirmed for both FI001 and FI004 isolates. Efficacies (as determined by nematode burden analysis) of 4, 21 and 31% for FI001, and 10, 1 and 74% for FI004, were obtained for IVM-INJ, IVM-PO and MOX-PO, respectively. Efficacy based on faecal egg count reduction at seven days post anthelmintic administration were 8, 99 and 100% for FI001, and 37, 20 and 100% for FI004 for IVM-INJ, IVM-PO and MOX-PO, respectively. In summary, this study details two macrocyclic lactone resistant isolates of C. oncophora obtained from cattle from two distinct geographical locales in the UK.

Parasitism by gastrointestinal nematodes is a health concern in New World Camelids (NWC) worldwide, and anthelmintic treatment is often needed for parasite control. Although anthelmintic resistance has been reported in ruminants worldwide, data in NWC are only scarce. In the present study, a case of suspected doramectin resistance in alpacas was examined. A field efficacy study was conducted for the evaluation of two different dosages of doramectin using a faecal egg count reduction test. A group of 8 alpacas was treated with a subcutaneous injection of doramectin at 0.2mg/kg bodyweight. Individual faecal samples were collected before treatment and 7 days after treatment. The faecal egg counts indicated a treatment efficacy of only 68%. To determine whether the treatment failure was caused by true anthelmintic resistance or suboptimal dosage in this animal species, a group of 4 alpacas was subsequently treated at 0.3mg/kg bodyweight. Faecal egg counts 7 days post treatment were reduced by only 41%, indicating that the treatment failure was more likely to be caused by the presence of resistant parasites on this farm. Coprocultures of faecal samples collected after treatment indicated the presence of 98.5% Haemonchus contortus and a small percentage of Cooperia oncophora (<1.5%). A controlled efficacy trial in sheep, for which the optimal dosage of doramectin is known, was conducted to ensure that this truly was a case of resistant parasites. Infective larvae collected from the faeces of these alpacas were used to infect eight nematode-free lambs. These lambs were assigned to one of two groups based on faecal egg counts post infection. One group was treated with doramectin injectable at 0.2mg/kg bodyweight, the other group served as a non treated control group. Pharmacokinetics indicated that the doramectin treatment was adequate, yet an efficacy of only 16% was determined on day 7 after treatment. Identification of the larvae after treatment revealed 100% H. contortus. On day 7 after treatment, H. contortus worm counts were only reduced by 8% in the treated lambs. The results of the present study report for the first time a case of doramectin resistance in alpacas, mainly in H. contortus.

The plasma kinetics disposition of moxidectin following a subcutaneous administration with a long-acting formulation (Cydectin® 10%, Fort Dodge Animal Health, France) at the recommended dose of 1mgkg−1 body weight was evaluated in Charolais cattle breed (five females weighing 425–450kg) for 120 days. Furthermore, its concentration was measured in hair for the same period. After plasma extraction and derivatization, samples were analysed by HPLC with fluorescence detection. Moxidectin was first detected at 1h after treatment for plasma (2.00±1.52ngml−1) and at 2 days for hair (446.44±193.26ngg−1). The peak plasma concentration (Cmax) was 55.71±15.59ngml−1 and 444.44±190.45ngg−1 for plasma and hair, respectively. The mean calculated time of peak occurrence (Tmax) was 3.40±3.36 and 2 days for plasma and hair, respectively. The mean residence time (MRT) was 28.93±2.87 and 13.32±2.48 days for plasma and hair cattle. The area under concentration–time curve (AUC) was 1278.95±228.92ngdayml−1 and 2663.82±1096.62ngdayg−1 for plasma and hair, respectively. At the last sampling time (120 days), the concentration was 1.91±0.26ngml−1 and 0.69±0.52ngg−1 for plasma and hair, respectively. The bioavailability of this long-acting formulation of moxidectin is similar to that registered after subcutaneous administration of moxidectin in cattle at 0.2mgkg−1 body weight. For the first time the moxidectin pharmacokinetics parameters in hair after a subcutaneous administration was described. The moxidectin profile concentrations in hair reflected that registered in plasma. The previous studies of efficacy have to be correlated to the extended period of absorption and distribution by the LA formulation due to the fivefold higher dose rate in comparison with the 1% injectable formulation (0.2mgkg−1 body weight).

The present study was conducted to investigate the effect of the administration site on the plasma kinetics of eprinomectin in five dromedary camels following a single pour-on administration (0.500 mg/kg bw). Three camels received uniformly the drug along the dorsal line, from the base of the tail to the withers, including hump whereas the others received the drug dose half administered in the withers region while the other half was given in the croup zone.The obtained results showed that the peak plasma concentration (C-max) was about two-fold higher and the area under plasma concentration curve (AUC) increased by 64% when the hump was excluded from the site of administration.

The pharmacokinetics and mammary excretion of eprinomectin were determined in zebu Gobra following topical administration of 0.5 mg kg(-1). The kinetics of plasma and milk was analysed using a one-compartment model. The maximum plasma concentration of 8.83+/-2.15 ng ml(-1) occurred 1.30 days post-administration. The area under the plasma concentration-time curve was 30.63+/-5.56 ng day(-1) ml(-1) and the mean residence time was 3.38+/-0.60 days. Eprinomectin was detected in milk at the first sampling time and thereafter for at least 8 days. The systemic availability of eprinomectin was significantly lower than that for other breeds of cattle. Comparison of the milk and plasma data demonstrated the parallel disposition of the drug in the milk and plasma with a milk/plasma ratio of 0.094. The very low extent of mammary excretion supports the permitted use of eprinomectin in lactating zebu Gobra.

The interaction of moxidectin (a macrocyclic lactone, ML) with P-glycoprotein (P-gp), multidrug resistance associated proteins (MRPs) and breast cancer resistance protein (BCRP) was studied in primary cultures of rat hepatocytes by measuring the intracellular accumulation of [14C]-moxidectin over 72 h in the presence of specific inhibitors: for P-gp, verapamil (10 microM); for MRPs, MK571 (100 microM), indomethacin (10 microM) and probenecid (3.8 mM); and for BCRP, fumitremorgin C (5 microM). The P-gp and MRP inhibitors increased significantly (P < 0.01) by 48.7%, 49.8%, 49.9% and 57.2% the area under the time-intracellular concentration curve (AUC) of moxidectin in rat hepatocytes, while the BCRP inhibitor, fumitremorgin C, had no effect on the AUC compared with the control. In addition, the mRNAs of all the drug transporters studied were detected in rat hepatocytes from 0 to 72 h. Using this cellular model it has been shown that MRP inhibitors increase moxidectin intracellular concentrations to a similar extent as the P-gp inhibitor. The identification of all the transporters that interact with MLs remains a challenge, which currently concerns several important therapeutic fields.

We have tested the ability of two compounds licensed in veterinary medicine: fumagillin and diminazene diaceturate to increase intracellular moxidectin quantity in rat hepatocytes. These compounds significantly increased the quantity of 14C-moxidectin (expressed as area under the time curve concentrations) in cultured rat hepatocytes by 44% and 65% for diminazene and fumagillin treatments respectively. In addition, we have tested these drugs for their interference with P-glycoprotein (P-gp) function in porcine kidney epithelial cells transfected with murine mdr1a (Mdr1a-LLCPK1). We examined the intracellular accumulation of rhodamine 123 (Rho 123) as a functional test to evaluate the effects of these two drugs on P-gp activity. In this model, only fumagillin led to a marked intracellular accumulation of Rho 123. After transforming the data to express the results as a percentage of the accumulation in the presence of the P-gp inhibitor valspodar (VSP), the maximal Rho 123 accumulation was 47% of that with VSP for 100 microm fumagillin. The EC50, the concentration needed to determine 50% of the maximal effect was 34 microm. Fumagillin interacts with P-gp function and appears as a promising compound among registered drugs available, which may optimize the therapeutic use of macrocyclic lactones (MLs).

Plasma disposition kinetics of ivermectin was evaluated in a West African cattle breed. Five clinically healthy zebu Gobra cattle (Bos indicus) weighing 220–270 kg were treated (0.2 mg kg−1) with a commercially available ivermectin formulation for cattle. Blood samples were collected by jugular puncture at different times between 0.5 h and 40 days post-treatment. After plasma extraction and derivatization, samples were analysed by HPLC with fluorescence detection. Ivermectin was detected in plasma between 30 min and 20 days post-treatment. The observed peak plasma concentration (Cmax) was 46.3 ± 13.8 ng ml−1 and the time to reach Cmax (tmax) was 0.9 ± 0.2 day. The values for the absorption half-life (t1/2ab) and the elimination half-life (t1/2el) were 0.3 ± 0.2 and 2.8 ± 0.7 days, respectively. The calculated area under the concentration–time curve (AUC) was 185.2 ± 12.1 ng day ml−1 and the mean residence time (MRT) was 4.2 ± 1.3 days. The availability of ivermectin is low in zebu Gobra in comparison to other breeds cattle but equivalent to that reported in the yak and is likely to be due to physiological characteristics of this breed.

The tissue concentration and efficacy of ivermectin after per os and subcutaneous administration were compared in goats experimentally infected with Trichostrongylus colubriformis (ivermectin-susceptible strain, INRA). Infected goats (n = 24) were treated per os (n = 9) or subcutaneously (n = 9) with ivermectin, 0.2 mg/kg, or kept as not treated controls. The faecal egg counts and small intestine worm counts were determined. Ivermectin concentration was measured in the plasma, gastrointestinal tract, lung, skin or hair, liver and adipose tissues at 0, 2, 7 and 17 days post-treatment. The efficacy of ivermectin against T. colubriformis infection in goat was 98.7 and 99.9% for subcutaneous and oral administration, respectively. Ivermectin concentration declined with time and only residual concentration was measured at 17 days post-treatment in plasma and gastrointestinal tract. Ivermectin concentration was higher after subcutaneous compared to per os injection in most of the tissue examined. In skin, hair and subcutaneous adipose tissue ivermectin persisted at significant concentrations 17 days post-treatment for both routes of administration. In our experimental conditions, ivermectin provides similar efficacy against T. colubriformis after subcutaneous or per os administration in goat. However, the lower ivermectin levels in tissues after per os administration suggest that the lasting of efficacy may be shortened after per os compared to subcutaneous administration especially in animals with poor body condition in pasture where re-infection occurs quickly after anthelmintic treatment.