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1.
Monepantel (MNP) is a novel anthelmintic compound launched into the veterinary pharmaceutical market. MNP is not licenced for use in dairy animals due to the prolonged elimination of its metabolite monepantel sulphone (MNPSO2) into milk. The goal of this study was to evaluate the presence of potential in vivo drug‐drug interactions affecting the pattern of milk excretion after the coadministration of the anthelmintics MNP and oxfendazole (OFZ) to lactating dairy cows. The concentrations of both parent drugs and their metabolites were measured in plasma and milk samples by HPLC. MNPSO2 was the main metabolite recovered from plasma and milk after oral administration of MNP. A high distribution of MNPSO2 into milk was observed. The milk‐to‐plasma ratio (M/P ratio) for this metabolite was equal to 6.75. Conversely, the M/P ratio of OFZ was 1.26. Plasma concentration profiles of MNP and MNPSO2 were not modified in the presence of OFZ. The pattern of MNPSO2 excretion into milk was also unchanged in animals receiving MNP plus OFZ. The percentage of the total administered dose recovered from milk was 0.09 ± 0.04% (MNP) and 2.79 ± 1.54% (MNPSO2) after the administration of MNP alone and 0.06 ± 0.04% (MNP) and 2.34 ± 1.38% (MNPSO2) after the combined treatment. The presence of MNP did not alter the plasma and milk disposition kinetics of OFZ. The concentrations of the metabolite fenbendazole sulphone tended to be slightly higher in the coadministered group. Although from a pharmacodynamic point of view the coadministration of MNP and OFZ may be a useful tool, the presence of OFZ did not modify the in vivo pharmacokinetic behaviour of MNP and therefore did not result in reduced milk concentrations of MNPSO2.  相似文献   
2.
The use of topical (pour-on) administration of endectocide drugs in cattle has reached world-wide acceptance. However, only limited information is available on the kinetic behaviour for topically administered moxidectin (MXD). To improve our understanding of the relationship between pharmacokinetics and efficacy for pour-on preparations, MXD concentration profiles were measured in tissues of endo- and ectoparasites location over 35 days postadministration. MXD distribution to the fluid content and mucosal tissue of the abomasum and different intestinal sections (duodenum, ileum, caecum and colon) was assessed. The comparative patterns of MXD distribution to skin and hypodermic tissue from different anatomical sites (backline, rib cage, thigh and face) were also investigated following the pour-on administration. Wide tissue distribution and long residence time characterized the kinetics of topically administered MXD. MXD was recovered between 1 and 35 days post-treatment in all the tissues investigated. The highest MXD availabilities were observed in the skin layers at the site of administration (backline) and in the fat tissue. The fluid contents of different intestinal sections showed MXD concentrations higher than those measured in their respective mucosal tissues, particularly at day 1 post-treatment. MXD concentrations in the skin (epidermis + dermis) were higher than those measured in the hypodermic tissue. Large differences in the availability of MXD in skin from different anatomical regions (backline > rib cage > thigh > face) were observed. The low plasma and the high skin availability indicate the formation of a skin depot of the drug, being released slowly to the plasma and reaching concentrations in systemic tissues (abomasal mucosa, lungs, etc.) similar to those measured after subcutaneous administration. These findings demonstrate that target parasites may be exposed to markedly different drug concentrations according to their location sites, which is particularly relevant for ectoparasites located in different anatomical regions. Knowledge of the tissue distribution of topically administered endectocides contributes to understand the differences observed in efficacy and/or persistence of activity and to optimize their use in cattle.  相似文献   
3.
The pharmacokinetic profile of avermectin and milbemycin compounds is affected by different drug- and host-related factors. This work reports the influence of cattle breeds on the plasma kinetics of moxidectin (MXD) after topical (pour-on) administration. Parasite-free Aberdeen Angus and Holstein calves were treated with a commercial MXD pour-on formulation at 500 microg/kg. Blood samples were collected over a period of 35 days post-treatment and the recovered plasma was analysed by high performance liquid chromatography using fluorescence detection. MXD was detected in plasma from two hours up to 35 days post-treatment in animals from both breeds. A slow MXD absorption and delayed peak plasma concentration were observed in Aberdeen Angus compared to Holstein calves. Significant lower systemic availability (expressed as AUC) (P<0.01) and peak plasma concentration (C(max)) (P<0.05) were also observed in Aberdeen Angus calves, although the plasma mean residence time (MRT) and elimination half-lives (T(1/2el)) of MXD in both breeds were similar. The pharmacokinetic differences observed between cattle breeds contribute to explain the variability in the pattern of clinical efficacy for pour-on administered endectocide compounds reported in different field trials.  相似文献   
4.
The family of ATP‐binding cassette (ABC) transporters is composed of several transmembrane proteins that are involved in the efflux of a large number of drugs including ivermectin, a macrocyclic lactone (ML) endectocide, widely used in human and livestock antiparasitic therapy. The aim of the work reported here was to assess the interaction between three different anthelmintic drugs with substrates of the P‐glycoprotein (P‐gp) and the breast cancer resistance protein (BCRP). The ability of ivermectin (IVM), moxidectin (MOX) and closantel (CST) to modulate the intestinal transport of both rhodamine 123 (Rho 123), a P‐gp substrate, and danofloxacin (DFX), a BCRP substrate, across rat ileum was studied by performing the Ussing chamber technique. Compared to the controls, Rho 123 efflux was significantly reduced by IVM (69%), CST (51%) and the positive control PSC833 (65%), whereas no significant differences were observed in the presence of MOX (30%). In addition, DFX efflux was reduced between 59% and 72% by all the assayed drug molecules, showing a higher potency than that observed in the presence of the specific BCRP inhibitor pantoprazole (PTZ) (52%). An ex vivo intestinal transport approach based on the diffusion chambers technique may offer a complementary tool to study potential drug interactions with efflux transporters such as P‐gp and BCRP.  相似文献   
5.
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 t½el 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.  相似文献   
6.
Different pharmacological approaches have been used in an attempt to increase the systemic availability of anthelmintic drugs. The comparative effect of the itraconazole (ITZ)-mediated modulation of P-glycoprotein (P-gp) activity on the in vivo kinetic behaviour of ivermectin (IVM) administered by the intravenous (i.v.) and intraruminal (i.r.) routes to sheep was assessed in the current work. Corriedale sheep received IVM (50 microg/kg) by the i.v. route either alone (group A) or co-administered with the P-gp modulator ITZ (100 mg orally three times every 12 h) (group B). Animals in groups C and D were intraruminally treated with IVM (50 microg/kg) alone or co-administered with ITZ (100 mg orally three times every 12 h) respectively. Jugular blood and gastrointestinal tissue samples (animals treated by the i.r. route) were collected. The samples were analysed by HPLC using fluorescence detection. The plasma disposition of IVM given intravenously was unaffected by the presence of ITZ. However, after the i.r. treatment the co-administration with ITZ resulted in markedly higher IVM plasma concentration profiles compared to the control group. Likewise, the presence of ITZ enhanced the IVM concentration profiles measured in the gastrointestinal mucosal tissues. An ITZ-induced reduction on the P-gp efflux activity at the intestinal lining may have accounted for the greater absorption and enhanced systemic availability observed for IVM in the intraruminally treated animals.  相似文献   
7.
Endectocide compounds are extensively used for broad-spectrum parasite control and their topical administration to cattle is widespread in clinical practice. Pour-on formulations of moxidectin, ivermectin, eprinomectin and doramectin (DRM) are marketed internationally for use in cattle. However, variability in antiparasitic efficacy and pharmacokinetic profiles has been observed. Although the tissue distribution pattern for different endectocide molecules given subcutaneously to cattle has been described, only limited information on drug concentration profiles in tissues of parasite location after topical treatment is available. Understanding the plasma and target tissue kinetics for topically-administered endectocide compounds is relevant to optimise their therapeutic potential. The current work was designed to measure the plasma and gastrointestinal (GI) concentration profiles of DRM following its pour-on administration to calves. The influence of natural licking behaviour of cattle on DRM concentration in mucosal tissue and luminal content of different GI sections was evaluated. The trial was conducted in two experimental phases. In Phase I, the DRM plasma kinetics was comparatively characterised in free-licking and in 2-day licking-restricted (non-licking) calves. The pattern of distribution of topical DRM to mucosal and luminal contents from abomasum, duodenum, ileum, caecum and spiral colon was assessed in free-licking and non-licking calves restricted over 10 days post-administration (Phase II). The prevention of licking caused marked changes on the plasma and GI kinetics of DRM administered pour-on. In 2-day licking restricted calves, DRM systemic availability was significantly lower (29%) than in free licking animals during the first 9 days post-treatment. Following a 10-day long licking restriction period, DRM concentrations profiles in both mucosal tissue and luminal contents of the GI tract were markedly higher in animals allowed to lick freely. This enhancement in drug concentrations in free-licking compared to non-licking calves, was particularly pronounced in the abomasal (38-fold higher) and duodenal (six-fold higher) luminal content. As shown earlier for ivermectin, licking behaviour may facilitate the oral ingestion of topically-administered DRM in cattle. This would be consistent with the marked lower drug concentration profiles measured in the bloodstream and GI tract of the animals prevented from licking. The work reported here provides relevant information on the pattern of DRM distribution to the GI tract after pour-on treatment, and contributes to understand the variability observed in the antiparasitic persistence of topically-administered endectocides in cattle. The implications of natural licking in topical treatments are required to be seriously assessed to achieve optimal parasite control and to design parasitological and pharmacological studies within the drug approval process.  相似文献   
8.
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.  相似文献   
9.
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 10 mg/kg live weight and ketoconazole at a dosage of 10 mg/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.  相似文献   
10.
Resistance to benzimidazole anthelmintics in the nematode Haemonchus contortus has been correlated with single nucleotide polymorphisms (SNPs) on the β-tubulin isotype 1 gene. Three mutations can be used as markers for the detection of resistance, namely SNPs at position 200 and 167 (both TTC to TAC) or at position 198 (GAA to GCA). Harbouring a resistance genotype at any one of these codons can lead to a resistant phenotype. Our objective in this study was to analyse the frequencies of the three mutations when the albendazole dose rate and selection pressure were increased. We used adult H. contortus (males and females) collected directly from the abomasum of untreated lambs, or lambs treated with the manufacturer's recommended dose rate (5mg/kg), three times the recommended dose rate (15 mg/kg), or nine times the recommended dose rate (45 mg/kg). Anthelmintic efficacy was determined by worm and egg count reductions. For the surviving worms of the four treatment groups, the frequencies of each resistance SNP at codons 167, 200 and 198 were measured using pyrosequencing. Our results showed a strong relationship between an increasing dose rate and an increase in the frequency of the (TAC)(200) SNP and a decrease in the (TAC)(167) SNP. All worms genotyped were GAA at codon 198.  相似文献   
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