Pharmacologic interaction between oxfendazole and triclabendazole: In vitro biotransformation and systemic exposure in sheep.

The aim of the current work was to evaluate a potential pharmacokinetic interaction between the flukicide triclabendazole (TCBZ) and the broad-spectrum benzimidazole (BZD) anthelmintic oxfendazole (OFZ) in sheep. To this end, both an in vitro assay in microsomal fractions and an in vivo trial in lambs parasitized with Haemonchus contortus resistant to OFZ and its reduced derivative fenbendazole (FBZ) were carried out. Sheep microsomal fractions were incubated together with OFZ, FBZ, TCBZ, or a combination of either FBZ and TCBZ or OFZ and TCBZ. OFZ production was significantly diminished upon coincubation of FBZ and TCBZ, whereas neither FBZ nor OFZ affected the S-oxidation of TCBZ towards its sulfoxide and sulfone metabolites. For the in vivo trial, lambs were treated with OFZ (Vermox® oral drench at a single dose of 5 mg/kg PO), TCBZ (Fasinex® oral drench at a single dose of 12 mg/kg PO) or both compounds at a single dose of 5 (Vermox®) and 12 mg/kg (Fasinex®) PO. Blood samples were taken to quantify drug and metabolite concentrations, and pharmacokinetic parameters were calculated by means of non-compartmental analysis. Results showed that the pharmacokinetic parameters of active molecules and metabolites were not significantly altered upon coadministration. The sole exception was the increase in the mean residence time (MRT) of OFZ and FBZ sulfone upon coadministration, with no significant changes in the remaining pharmacokinetic parameters. This research is a further contribution to the study of metabolic drug-drug interactions that may affect anthelmintic efficacies in ruminants.

Assessment of the pharmacological interactions between the nematodicidal fenbendazole and the flukicidal triclabendazole: In vitro studies with bovine liver microsomes and slices.

Parasitic diseases have a significant impact on livestock production. Nematodicidal drugs, such as fenbendazole (FBZ) or its oxidized metabolite oxfendazole (OFZ), can be used along with the trematodicidal triclabendazole (TCBZ), to broaden the spectrum of anthelmintic activity. However, co-exposure to these compounds could lead to drug-drug (D-D) interactions and eventually alter the clinical profile of each active principle. The aim of this study was to assess the presence of such interactions by means of two in vitro models, namely bovine liver microsomal fractions and bovine precision-cut liver slices (PCLSs). To this end, an in vitro assessment involving incubation of FBZ and TCBZ or a combination of FBZ and TCBZ was carried out. Results with microsomal fractions showed a 78.4% reduction (p = .002) in the rate of OFZ production upon co-incubation, whereas the sulfoxide metabolite of TCBZ (TCBZSO) exhibited a decreasing tendency. With PCLS, OFZ accumulation in the incubation medium increased 1.8-fold upon co-incubation, whereas TCBZSO accumulation decreased by 28%. The accumulation of FBZ and OFZ in the liver tissue increased upon 2-hr co-incubation, from 2.1 ± 1.5 to 18.2 ± 6.1 (p = .0009) and from 0.4 ± 0.1 to 1.3 ± 0.3 nmol (p = .0005), respectively. These results confirm the presence of D-D interactions between FBZ and TCBZ. Further studies are needed to determine the extent of involvement of drug-metabolizing enzymes and membrane transporters in interactions between compounds largely used in livestock production systems.

Comparative in vitro characterization of moxidectin and doramectin percutaneous absorption through bovine skin.

Topical formulations have achieved worldwide acceptance in veterinary medicine because their administration is an easy, less labor-intensive and nonstressing form. Any chemical compound that comes in contact with the skin has the potential to be locally and/or systemically absorbed. However, many factors related to the features of animal skin, composition of the topical formulation and to the drug itself can determine marked differences in the percutaneous absorption process. The aim of the current work was to characterize the pattern of in vitro percutaneous absorption for moxidectin (MXD) and doramectin (DRM), two of the most worldwide used topical macrocyclic lactone antiparasitic compounds in cattle. The work included the development of a simple and inexpensive in vitro assay useful to predict in vivo drug percutaneous absorption in cattle. Both drugs were administered as the commercial formulations intended for their topical administration to cattle. The in vitro studies were carried out using modified Franz-type vertical diffusion cells. Cattle skin slices of 500 µm thickness were prepared using a dermatome to separate the stratum corneum and upper epidermis from dermis and subcutaneous tissue. The receptor medium was sampled up to 72 h postadministration and drug concentrations were measured by HPLC. The parameters used to estimate the comparative in vitro skin permeation showed marked differences between DRM and MXD. A 5.29-fold longer lag time (T(lag)) was observed for DRM. Similarly, the flux (J) (2.93-fold) and the permeation coefficients (K(p) ) (2.95-fold) in cattle skin were significantly higher (P < 0.05) for DRM compared to those obtained for MXD. Additionally, the data obtained from the in vitro permeation studies was correlated with the plasma concentrations of both compounds achieved in vivo in cattle treated with the same topical formulations. Correlation coefficients between percentage of drug permeated in vitro vs. percentage of drug absorbed in vivo (up to 48 h post-treatment) were 0.856-0.887 (MXD) and 0.976-0.990 (DRM). However, the highest in vitro-in vivo correlations for both molecules were observed up to 24 h post-treatment A rapid screening method for testing different topical formulations can be achieved with the simple in vitro cattle skin permeation technique described here, which has been successfully adapted to test the comparative percutaneous absorption of MXD and DRM.

Gaining Insights Into the Pharmacology of Anthelmintics Using Haemonchus contortus as a Model Nematode.

Progress made in understanding pharmacokinetic behaviour and pharmacodynamic mechanisms of drug action/resistance has allowed deep insights into the pharmacology of the main chemical classes, including some of the few recently discovered anthelmintics. The integration of pharmaco-parasitological research approaches has contributed considerably to the optimization of drug activity, which is relevant to preserve existing and novel active compounds for parasite control in livestock. A remarkable amount of pharmacology-based knowledge has been generated using the sheep abomasal nematode Haemonchus contortus as a model. Relevant fundamental information on the relationship among drug influx/efflux balance (accumulation), biotransformation/detoxification and pharmacological effects in parasitic nematodes for the most traditional anthelmintic chemical families has been obtained by exploiting the advantages of working with H. contortus under in vitro, ex vivo and in vivo experimental conditions. The scientific contributions to the pharmacology of anthelmintic drugs based on the use of H. contortus as a model nematode are summarized in the present chapter.

Influence of 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 on expression of P-glycoprotein and cytochrome P450 3A in sheep.

In order to improve calcium and phosphorus balance, beef cattle and dairy cows can be supplemented with vitamin D. However, different vitamin D metabolites have been shown to increase expression of P-glycoprotein (P-gp, MDR1, ABCB1) and cytochrome P450 3A (CYP3A) in rodents as well as in cell culture systems. As such interferences might have an impact on pharmacokinetics of some drugs widely-used in veterinary medicine, we investigated the expression of P-gp, CYP3A, vitamin D receptor (VDR), pregnane X receptor (PXR) and retinoid X receptor α (RXRα) in sheep either treated orally with 6µg/kg body weight (BW) 25-hydroxyvitamin D3 (OHD3) for ten days before sacrifice or 12h after intravenous injection of 0.5µg/kg BW 1,25-dihydroxyvitamin D3 (1,25- (OH)2D3). Down-regulation of ruminal, jejunal and hepatic, but not renal P-gp could be found with 25-OHD3 supplementation. Interestingly, this effect on P-gp was not observed in tissues from 1,25-(OH)2D3-treated sheep. In contrast, 1,25-(OH)2D3 induced a significant up-regulation of renal and jejunal CYP3A expression, while 25-OHD3 had no impact. Renal expression of VDR and PXR was also increased by treatment with 1,25-(OH)2D3, while jejunal PXR expression was only stimulated in sheep supplemented with 25-OHD3. Either treatments increased renal, but not ruminal, jejunal or hepatic expression of RXRα. These results demonstrate that the impact of large doses of vitamin D metabolites on different target organs and potential interactions with other medications should be further investigated in vitro and in vivo to understand the effects of vitamin D metabolites on metabolism and excretion pathways in livestock.

Ricobendazole kinetics and availability following subcutaneous administration of a novel injectable formulation to calves.

The plasma and abomasal fluid disposition kinetics of ricobendazole (RBZ) after subcutaneous (s.c.) administration of a novel injectable formulation to calves, and the comparative plasma availability after s.c. injection of RBZ and that obtained after oral treatment with albendazole (ABZ), were characterised. Six parasite-free Holstein calves received RBZ (solution 150 mg ml(-1)) by s.c. injection at 3.75 mg kg(-1) (Experiment 1). Experiment 2 was conducted in two experimental phases; in phase I, five calves (Group A) received RBZ by s.c. injection and five animals (Group B) were orally treated with ABZ (suspension 100 mg ml(-1)), at 5 mg kg(-1). Drug treatments were reversed for each group in phase II and given at 7.5 mg kg(-1). Samples of abomasal fluid (via cannula) and jugular blood were collected over 72 hours post-treatment and analysed by HPLC. RBZ and its sulphone metabolite were detected in plasma following its s.c. administration. RBZ was rapidly absorbed, reaching the plasma Cmax at 4.5 hours post-dosing. The sulphone metabolite followed a similar kinetic pattern. Both molecules were rapidly and extensively distributed into the abomasum, being detected in abomasal fluid between 30 minutes and 36 hours post-administration. An extensive plasma/abomasum exchange process, with ionic-trapping in the abomasum, accounted for the higher AUC value (>200 per cent) obtained for RBZ in abomasum compared with plasma. The s.c. treatment with RBZ formulated as a solution resulted in a significantly greater plasma availability (measured as ABZ sulphoxide) than the oral treatment with ABZ (suspension) given at the same dose rates.

Pharmacokinetics of eprinomectin in plasma and milk following subcutaneous administration to lactating dairy cattle.

Eprinomectin is only available as a topically applied anthelmintic for dairy cattle. To determine whether eprinomectin can be applied as an injectable formulation in dairy cattle, a novel injectable formulation was developed and was subcutaneously delivered to four lactating dairy cattle at a dose rate of 0.2 mg/ kg. Plasma and milk samples were collected. The concentrations of eprinomectin in all samples were determined by HPLC. The peak plasma concentration (C(max))of 44.0+/-24.2 ng/ml occurred 39+/-19.3 h after subcutaneous administration, equivalent to the C(max) (43.76+/-18.23 ng/ml) previously reported for dairy cattle after a pour-on administration of 0.5 mg/kg eprinomectin. The area under the plasma concentration-time curve (AUC) after subcutaneous administration was 7354+/-1861 (ng h)/ml, higher than that obtained after pour-on delivery (5737.68+/-412.80 (ng h)/ml). The mean residence time (MRT) of the drug in plasma was 211+/-55.2 h. Eprinomectin was detected in the milk at the second sampling time. The concentration of drug in milk was parallel to that in plasma, with a milk to plasma ratio of 0.16+/-0.01. The highest detected concentration of eprinomectin in milk was 9.0 ng/ml, below the maximum residue limit (MRL) of eprinomectin in milk established by the Joint FAO/WHO Expert Committee on Food Additives in 2000. The amount of eprinomectin recovered in the milk during this trial was 0.39%+/-0.08% of the total administered dose. This study demonstrates that subcutaneous administration of eprinomectin led to higher bioavailability and a lower dose than a pour-on application, and that an injectable formulation of eprinomectin may be applied in dairy cattle with a zero withdrawal period.

Environmental impact of ivermectin excreted by cattle treated in autumn on dung fauna and degradation of faeces on pasture.

The effect of ivermectin excreted in faeces of treated cattle on dung fauna and dung degradation on pasture during autumn was evaluated. Two groups of calves were used. One group was treated subcutaneously with ivermectin while the other remained as untreated control. Faeces deposited on 1, 3, 7, 14 and 21 days post-treatment (dpt) were removed on 1, 3, 7, 14, 21, 30 and 60 days post-deposition (dpd) and were used to determine the concentration of ivermectin and the percentage of organic matter and for the collection of colonising organisms. Samples from 1 and 3 dpt contained the highest drug concentration and percentage of organic matter compared to the control group (p<0.05). Faeces from the treated group showed lesser abundance and diversity of arthropods (p<0.05) than the control group. A reduction in numbers and diversity of dung fauna in faecal samples from treated animals was most remarkable at 1, 3 and 7 dpt, coinciding with the highest concentration of ivermectin and organic matter percentage.

[Comparative evaluation of modern intraoperative diagnostic methods in malignant gliomas of the brain]. / Vergleichsbeurteilung moderner Methoden der intraoperativen Diagnostik maligner Gliome des Gehirns.

The following methods were employed: Intravital staining with bromphenol blue (70 patients), radiometry with P 32 (127 patients), echo encephalography (12 patients,) puncture biopsy (18 patients), rheometry (96 patients). Bromphenol blue is injected into the a. cerebri media or the supraclinoidal a. carotis interna and stains the periphery of malignant tumours and the entire tissue of benign tumours. Radiometry also serves for the intraoperative finding of tumour remainders which must be located at least 20 to 22 mm below the cortex of the brain. Tumour biopsy was carried out with a sharp cannula to avoid deformation of the tissue cylinder. Rheometry proved to be very useful when avoiding the mixing with blood, liquor, and cyst fluid at the measuring tip.