Graphical abstractHighlights► Macrocyclic lactones share some structural and physico-chemical properties. ► The kinetic-dynamic differences of these compounds should be addressed under in vivo standardized conditions. ► Lower concentrations of moxidectin were obtained in resistant Haemonchus contortus. ► Moxidectin showed a higher efficacy against resistant H. contortus. ► The P-glycoprotein expression in H. contortus was increased after ivermectin treatment.

ABSTRACT:The everted gut sac method was used to assess the role of the P-glycoprotein (P-gp) on the intestinal secretion of ivermectin (IVM), an antiparasitic widely used in human and veterinary medicine. The work included the evaluation of two different P-gp modulators [itraconazole (ITZ) and valspodar (PSC833)] used at equimolar doses in the rat. Furthermore, the influence of both P-gp modulator agents on the disposition kinetics of IVM in plasma, liver, and gastrointestinal tissues was characterized.

Flubendazole (FLBZ) is a broad-spectrum benzimidazole anthelmintic compound used in pigs, poultry and humans. Its potential for parasite control in ruminant species is under investigation. The objective of the work described here was to identify the main enzymatic pathways involved in the hepatic and extra-hepatic biotransformation of FLBZ in sheep. Microsomal and cytosolic fractions obtained from sheep liver and duodenal mucosa metabolised FLBZ into a reduced FLBZ metabolite (red-FLBZ). The keto-reduction of FLBZ led to the prevalent (approximately 98%) stereospecific formation of one enantiomeric form of red-FLBZ. The amounts of red-FLBZ formed in liver subcellular fractions were 3-4-fold higher (P<0.05) compared to those observed in duodenal subcellular fractions. This observation correlates with the higher (P<0.05) carbonyl reductase (CBR) activities measured in the liver compared to the duodenal mucosa. No metabolic conversion was observed following FLBZ or red-FLBZ incubation with sheep ruminal fluid. Sheep liver microsomes failed to convert red-FLBZ into FLBZ. However, this metabolic reaction occurred in liver microsomes prepared from phenobarbital-induced rats, which may indicate a cytochrome P450-mediated oxidation of red-FLBZ. A NADPH-dependent CBR is proposed as the main enzymatic system involved in the keto-reduction of FLBZ in sheep. CBR substrates such as menadione and mebendazole (a non-fluoride analogue of FLBZ), inhibited this liver microsomal enzymatic reaction, which may confirm the involvement of a CBR enzyme in FLBZ metabolism in sheep. This research is a further contribution to the understanding of the metabolic fate of a promissory alternative compound for antiparasitic control in ruminant species.

In human and mice ATP-binding cassette efflux transporter ABCG2 represents the main route for active drug transport into milk. However, there is no detailed information on the role of ABCG2 in drug secretion and accumulation in milk of dairy animals. We therefore examined ABCG2-mediated drug transport in the bovine mammary gland by parallel pharmacokinetic studies in lactating Jersey cows and in vitro flux studies using the anthelmintic drug monepantel (MNP) as representative bovine ABCG2 (bABCG2) drug substrate. Animals received MNP (Zolvix, Novartis Animal Health Inc.) once (2.5 mg/kg per os) and the concentrations of MNP and the active MNP metabolite MNPSO2 were assessed by high-performance liquid chromatography. Compared with the parent drug MNP, we detected higher MNPSO2 plasma concentrations (expressed as area under the concentration-versus-time curve). Moreover, we observed MNPSO2 excretion into milk of dairy cows with a high milk-to-plasma ratio of 6.75. In mechanistic flux assays, we determined a preferential time-dependent basolateral-to-apical (B > A) MNPSO2 transport across polarized Madin-Darby canine kidney II cells-bABCG2 monolayers using liquid chromatography coupled with tandem mass spectrometry analysis. The B > A MNPSO2 transport was significantly inhibited by the ABCG2 inhibitor fumitremorgin C in bABCG2- but not in mock-transduced MDCKII cells. Additionally, the antibiotic drug enrofloxacin, the benzimidazole anthelmintic oxfendazole and the macrocyclic lactone anthelmintic moxidectin caused a reduction in the MNPSO2(B > A) net efflux. Altogether, this study indicated that therapeutically relevant drugs like the anthelmintic MNP represent substrates of the bovine mammary ABCG2 transporter and may thereby be actively concentrated in dairy milk.