Combined use of ivermectin and triclabendazole in sheep: in vitro and in vivo characterisation of their pharmacological interaction

Characterization of P-glycoprotein orthologs from human, sheep, pig, dog, and cat

The ATP-binding cassette transporter P-glycoprotein (P-gp) limits the oral bioavailability of many drugs. Although P-gp has been well studied in humans and mice, little is known about the substrate specificities of many of its species orthologs. To address this, we performed in vitro analysis of P-gp transporter function using HEK293 cells stably expressing human, ovine, porcine, canine, and feline P-gp. We also employed a human physiologically based pharmacokinetic (PBPK) model to assess variations in digoxin exposure resulting from altered P-gp function. Compared to human P-gp, sheep P-gp had significantly less digoxin efflux (2.3-fold ±0.04 vs. 1.8-fold ±0.03, p < .0001) and all species orthologs had significantly less quinidine efflux compared with human P-gp (p < .05). Human P-gp also had significantly greater efflux of talinolol compared to sheep and dog P-gp (1.9-fold ±0.04 vs. 1.6-fold ±0.06, p = .003 and 1.6-fold ±0.05, p = .0002, respectively). P-gp expression protected all lines against paclitaxel-induced toxicity, with sheep P-gp being significantly less protective. The inhibitor verapamil demonstrated dose-dependent inhibition of all P-gp orthologs. Finally, a PBPK model showed digoxin exposure was sensitive to altered P-gp activity. Overall, our study found that species differences in this major drug transporter exist and that the appropriate species ortholog of P-gp should be evaluated during veterinary drug development.

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.

Drug resistance in liver flukes

Liver flukes include Fasciola hepatica, Fasciola gigantica, Clonorchis sinensis, Opisthorchis spp., Fascioloides magna, Gigantocotyle explanatum and Dicrocoelium spp. The two main species, F. hepatica and F. gigantica, are major parasites of livestock and infections result in huge economic losses. As with C. sinensis, Opisthorchis spp. and Dicrocoelium spp., they affect millions of people worldwide, causing severe health problems. Collectively, the group is referred to as the Food-Borne Trematodes and their true significance is now being more widely recognised. However, reports of resistance to triclabendazole (TCBZ), the most widely used anti-Fasciola drug, and to other current drugs are increasing. This is a worrying scenario. In this review, progress in understanding the mechanism(s) of resistance to TCBZ is discussed, focusing on tubulin mutations, altered drug uptake and changes in drug metabolism. There is much interest in the development of new drugs and drug combinations, the re-purposing of non-flukicidal drugs, and the development of new drug formulations and delivery systems; all this work will be reviewed. Sound farm management practices also need to be put in place, with effective treatment programmes, so that drugs can be used wisely and their efficacy conserved as much as is possible. This depends on reliable advice being given by veterinarians and other advisors. Accurate diagnosis and identification of drug-resistant fluke populations is central to effective control: to determine the actual extent of the problem and to determine how well or otherwise a treatment has worked; for research on establishing the mechanism of resistance (and identifying molecular markers of resistance); for informing treatment options; and for testing the efficacy of new drug candidates. Several diagnostic methods are available, but there are no recommended guidelines or standardised protocols in place and this is an issue that needs to be addressed.

The Statistical Analysis of Pharmacokinetic Parameters in the Context of Bioequivalence Testing of Two Anthelmintic Formulas Based on Ivermectine and Triclabendazole in Sheep

Conducting bioequivalence studies is an essential step during the market authorization process of generic pharmaceutical formulations, for both human or veterinary use. The aim of the present study was to evaluate the pharmacokinetics of triclabendazole sulphoxide, the main metabolite of triclabendazole, and ivermectin in order to evaluate the bioavailability and bioequivalence of a novel sheep anthelmintic formulation of oral suspension for sheep treatment containing triclabendazole 50 mg/mL and ivermectin 1 mg/mL compared to the reference product. In order to determine relative bioavailability of the test product with respect to the reference product the study was conducted on 36 clinically healthy sheep, following an unicentric, randomized, cross-over, two-sequence, two-treatment and 14-day wash-out study design. For the determination of triclabendazole sulphoxide and ivermectin sheep plasma concentrations, two rapid, selective high performance liquid chromatography coupled with mass spectrometry (LC-MS/MS) methods were developed and validated. The measured plasma concentrations of triclabendazole sulphoxide and ivermectin were used for the pharmacokinetic analysis and the determination of bioequivalence between the test product with regards to the reference product. The noncompartmental analysis of the pharmacokinetic data for both triclabendazole sulphoxide and ivermectin showed similarities between first-order kinetics of the test and reference product. The relevant pharmacokinetic parameters (Cmax, AUClast, AUCtot) were determined and the bioequivalence between the test and reference product could be concluded.

Assessment of the long-acting ivermectin formulation in sheep: Further insight into potential pharmacokinetic interactions

The aim of the current study was to evaluate the in vivo pharmacokinetic of ivermectin (IVM) after the administration of a long-acting (LA) formulation to sheep and its impact on potential drug-drug interactions. The work included the evaluation of the comparative plasma profiles of IVM administered at a single therapeutic dose (200 μg/kg) and as LA formulation at 630 μg/kg. Additionally, IVM was measured in different gastrointestinal tissues at 15 days posttreatment with both IVM formulations. The impact of the long-lasting and enhanced IVM exposure on the disposition kinetics of abamectin (ABM) was also assessed. Plasma (IVM and ABM) and gastrointestinal (IVM) concentrations were analyzed by HPLC with fluorescent detection. In plasma, the calculated C_max and AUC_0-t values of the IVM-LA formulation were 1.47- and 3.35-fold higher compared with IVM 1% formulation, respectively. The T_1/2ab and T_max collected after administration of the LA formulation were 2- and 3.5-fold longer than those observed after administration of IVM 1% formulation, respectively. Significantly higher IVM concentrations were measured in the intestine mucosal tissues and luminal contents with the LA formulation, and in the liver, the increase was 7-fold higher than conventional formulation. There was no drug interaction between IVM and ABM after the single administration of ABM at 15 days post-administration of the IVM LA formulation. The characterization of the kinetic behavior of the LA formulation to sheep and its potential influence on drug-drug interactions is a further contribution to the field.

Population variability in animal health: Influence on dose-exposure-response relationships: Part I: Drug metabolism and transporter systems

There is an increasing effort to understand the many sources of population variability that can influence drug absorption, metabolism, disposition, and clearance in veterinary species. This growing interest reflects the recognition that this diversity can influence dose-exposure-response relationships and can affect the drug residues present in the edible tissues of food-producing animals. To appreciate the pharmacokinetic diversity that may exist across a population of potential drug product recipients, both endogenous and exogenous variables need to be considered. The American Academy of Veterinary Pharmacology and Therapeutics hosted a 1-day session during the 2017 Biennial meeting to explore the sources of population variability recognized to impact veterinary medicine. The following review highlights the information shared during that session. In Part I of this workshop report, we consider sources of population variability associated with drug metabolism and membrane transport. Part II of this report highlights the use of modeling and simulation to support an appreciation of the variability in dose-exposure-response relationships.

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.

Evaluation of pharmacokinetics and efficacy of ivermectin following oral administration in dogs against experimental infection of Ctenocephalides felis felis and Rhipicephalus sanguineus

With the increasing number of pets in home the human-animal relationship is increasingly close and care about control disease growing. Ivermectin (IVM) is frequently used because its proven safety. IVM is recommended for the treatment of demodectic scabies and prevention of heartworm in dogs, but informally is extremely used to control of Ctenocephalides felis felis and Rhipicephalus sanguineus. The aim of this study is evaluate the use of IVM in dogs, by the oral route at 0.6μg/kg dose, against experimental infection of these parasites using the construction of the plasma concentration curve and efficacy study. A IVM quantification method in canine plasma using HPLC-FL was developed and validated based on RE n°899/03 ANVISA. The samples collected during the efficacy test was analyzed by this validated method and prove C_max of 350ng/mL at 4h (t_max) and AUC of 8411ng/h/mL. Spite of formulation have shown good absorption, the highest efficiency values found for Rhipcephalus sanguineus and Ctenocephalides felis felis were very low, 35% and 67% respectively, demonstrating this not be the most appropriate treatment for the control of these parasites.

Pharmacokinetic evaluation of different generic triclabendazole formulations in heifers

AIMS

To assess the comparative drug systemic exposure of a reference (RF) and four test (Test I, Test II, Test III and Test IV) formulations of triclabendazole (TCBZ) in heifers.

METHODS

Thirty Holstein heifers were randomly distributed into five groups (n=6 per group). Animals in the RF group received the reference formulation (Fasinex), and those in the other groups received different commercially available TCBZ formulations (Test I, Test II, Test III and Test IV). All treatments were orally administered at 12 mg/kg bodyweight. The concentrations of TCBZ metabolites in plasma between 0 and 168 hours after treatment were quantified by high-performance liquid chromatography (HPLC).

RESULTS

Triclabendazole sulphoxide (TCBZ.SO) and TCBZ-sulphone (TCBZ.SO₂) were the only analytes recovered in plasma. Only the Test I formulation did not differ from the RF for all pharmacokinetic parameters measured for either metabolite (p>0.8). The TCBZ.SO area under the concentration vs. time curve for Test II formulation (268.9 µg.h/mL) was lower, and for Test III (619.9 µg.h/mL) and Test IV (683.4 µg.h/mL) was higher, than the RF (418.1 µg.h/mL) (p<0.005).

CONCLUSION

Based on the currently available bioequivalence criteria, the only test formulation under evaluation that could be considered equivalent to the RF was the Test I formulation, which demonstrated an equivalent systemic exposure for the active TCBZ.SO metabolite. This comparison of TCBZ pioneer and test formulations in cattle raises awareness of the need for further quality control for drug approval in the veterinary pharmaceutical field in many regions of the world.

Pharmacological knowledge and sustainable anthelmintic therapy in ruminants

Considering the increasing concern for the development of anthelmintic resistance, the use of pharmacology-based information is critical to design successful strategies for the future of parasite control in livestock. Integrated evaluation of the available knowledge on pharmacological features is required to optimize the activity and to achieve sustainable use of the existing anthelmintic drugs. The assessment of the drug disposition in the host and the comprehension of the mechanisms of drug influx/efflux/detoxification in different target helminths, has signified a relevant progress on the understanding of the pharmacology of anthelmintic drugs in ruminant species. However, additional scientific knowledge on how to improve the use of available and novel molecules is required to avoid/delay resistance development. Different pharmacokinetic-based approaches to enhance parasite exposure and the use of mixtures of drugs from different chemical families have been proposed as valid strategies to delay the development of anthelmintic resistance. The rationale behind using drug combinations is based on the fact that individual worms may have a lower degree of resistance to a multiple component formulation (each chemical with different mode of action/resistance) compared to that observed when a single anthelmintic is used. However, the limited available information is unclear on the potential additive or synergistic effects occurring after co-administration of two (or more) drugs with different mode of action. This review article contributes to the topic with some pharmacology-based data emerging from the assessment of combined anthelmintic preparations. The activity against multi-drug-resistant isolates based on novel modes of action is a highly favorable element to judge the future of some of the recently developed anthelmintic compounds. More specific knowledge on the basic host-parasite kinetic behavior as well as a highly responsible use of those novel compounds will be necessary to secure their maximum lifespans. Overall, the outcome from integrated pharmaco-parasitological research approaches has greatly contributed to optimize drug activity, which seems relevant to preserve existing and particularly novel active ingredients as useful tools for parasite control in livestock animals.

The anthelmintic triclabendazole and its metabolites inhibit the membrane transporter ABCG2/BCRP

ABCG2/BCRP is an ATP-binding cassette transporter that extrudes compounds from cells in the intestine, liver, kidney, and other organs, such as the mammary gland, affecting pharmacokinetics and milk secretion of antibiotics, anticancer drugs, and other compounds and mediating drug-drug interactions. In addition, ABCG2 expression in cancer cells may directly cause resistance by active efflux of anticancer drugs. The development of ABCG2 modulators is critical in order to improve drug pharmacokinetic properties, reduce milk secretion of xenotoxins, and/or increase the effective intracellular concentrations of substrates. Our purpose was to determine whether the anthelmintic triclabendazole (TCBZ) and its main plasma metabolites triclabendazole sulfoxide (TCBZSO) and triclabendazole sulfone (TCBZSO(2)) inhibit ABCG2 activity. ATPase assays using human ABCG2-enriched membranes demonstrated a clear ABCG2 inhibition exerted by these compounds. Mitoxantrone accumulation assays using murine Abcg2- and human ABCG2-transduced MDCK-II cells confirmed that TCBZSO and TCBZSO(2) are ABCG2 inhibitors, reaching inhibitory potencies between 40 and 55% for a concentration range from 5 to 25 μM. Transepithelial transport assays of ABCG2 substrates in the presence of both TCBZ metabolites at 15 μM showed very efficient inhibition of the Abcg2/ABCG2-mediated transport of the antibacterial agents nitrofurantoin and danofloxacin. TCBZSO administration also inhibited nitrofurantoin Abcg2-mediated secretion into milk by more than 2-fold and increased plasma levels of the sulfonamide sulfasalazine by more than 1.5-fold in mice. These results support the potential role of TCBZSO and TCBZSO(2) as ABCG2 inhibitors to participate in drug interactions and modulate ABCG2-mediated pharmacokinetic processes.

P-glycoproteins and other multidrug resistance transporters in the pharmacology of anthelmintics: Prospects for reversing transport-dependent anthelmintic resistance

Parasitic helminths cause significant disease in animals and humans. In the absence of alternative treatments, anthelmintics remain the principal agents for their control. Resistance extends to the most important class of anthelmintics, the macrocyclic lactone endectocides (MLs), such as ivermectin, and presents serious problems for the livestock industries and threatens to severely limit current parasite control strategies in humans. Understanding drug resistance is important for optimizing and monitoring control, and reducing further selection for resistance. Multidrug resistance (MDR) ABC transporters have been implicated in ML resistance and contribute to resistance to a number of other anthelmintics. MDR transporters, such as P-glycoproteins, are essential for many cellular processes that require the transport of substrates across cell membranes. Being overexpressed in response to chemotherapy in tumour cells and to ML-based treatment in nematodes, they lead to therapy failure by decreasing drug concentration at the target. Several anthelmintics are inhibitors of these efflux pumps and appropriate combinations can result in higher treatment efficacy against parasites and reversal of resistance. However, this needs to be balanced against possible increased toxicity to the host, or the components of the combination selecting on the same genes involved in the resistance. Increased efficacy could result from modifying anthelmintic pharmacokinetics in the host or by blocking parasite transporters involved in resistance. Combination of anthelmintics can be beneficial for delaying selection for resistance. However, it should be based on knowledge of resistance mechanisms and not simply on mode of action classes, and is best started before resistance has been selected to any member of the combination. Increasing knowledge of the MDR transporters involved in anthelmintic resistance in helminths will play an important role in allowing for the identification of markers to monitor the spread of resistance and to evaluate new tools and management practices aimed at delaying its spread.

Influence of P-glycoprotein inhibition on secretion of ivermectin and doramectin by milk in lactating sheep

The aim of to the present study was to evaluate the effects of verapamil (VER) on plasma pharmacokinetics of ivermectin (IVM) and doramectin (DOR) in lactating Istrian Pramenka dairy sheep and to investigate the role of P-glycoprotein (P-gp) in transport of avermectins into milk. Pharmacokinetics of IVM and DOR following subcutaneous administration of 0.2mg/kg b.w. was evaluated in four groups of sheep. They were administered either IVM or DOR alone or in combination with verapamil (VER) at a dose of 3.0mg/kg b.w., 3 times at 12h intervals. Blood plasma and milk samples were collected at defined time intervals over 30 days post-treatment to determine IVM and DOR concentration levels. Pharmacokinetic parameters in sheep injected with IVM or DOR alone corresponded to previously published values. Comparison between sheep injected with IVM only, and sheep injected with IVM in combination with VER (IVM+VER) showed significant difference in pharmacokinetic parameters in blood plasma. Area under the concentration-time curve (AUC) truncated at 2 days (AUC(2)) was 15 and 28 μg day/L for group IVM and IVM+VER, respectively. With co-administration of VER, apparent plasma clearance (Cl/F) and mean residence time (MRT) of IVM decreased from 135 to 116 L/day and from 5.8 to 3.8 days, respectively. Similar trends were observed for DOR (AUC(2) 48 vs. 68 μg day/L, Cl/F 61 vs. 46 L/day, and MRT 5.6 vs. 4.4 days for groups DOR and DOR+VER, respectively). This study confirms that co-administration of VER has a significant effect on pharmacokinetic parameters of subcutaneously administered IVM in blood plasma. The influence on DOR pharmacokinetics is much weaker. This could be either due to the difference in lipophilicity or the difference in affinity towards P-gp as a result of structural differences. No significant influence of VER on AUC ratio of IVM and DOR between milk and plasma was observed suggesting that P-gp does not govern transport of avermectins into milk.

Unchanged triclabendazole kinetics after co-administration with ivermectin and methimazole: failure of its therapeutic activity against triclabendazole-resistant liver flukes

BACKGROUND

The reduced drug accumulation based on enhanced drug efflux and metabolic capacity, identified in triclabendazole (TCBZ)-resistant Fasciola hepatica may contribute to the development of resistance to TCBZ. The aim of this work was to evaluate the pharmacokinetics and clinical efficacy of TCBZ administered alone or co-administered with ivermectin (IVM, efflux modulator) and methimazole (MTZ, metabolic inhibitor) in TCBZ-resistant F. hepatica-parasitized sheep. Sheep infected with TCBZ-resistant F. hepatica (Sligo isolate) were divided into three groups (n = 4): untreated control, TCBZ-treated (i.r. at 10 mg/kg) and TCBZ+IVM+MTZ treated sheep (10 i.r., 0.2 s.c. and 1.5 i.m. mg/kg, respectively). Plasma samples were collected and analysed by HPLC. In the clinical efficacy study, the animals were sacrificed at 15 days post-treatment to evaluate the comparative efficacy against TCBZ-resistant F. hepatica.

RESULTS

The presence of IVM and MTZ did not affect the plasma disposition kinetics of TCBZ metabolites after the i.r. administration of TCBZ. The AUC value of TCBZ.SO obtained after TCBZ administration (653.9 +/- 140.6 microgxh/ml) was similar to that obtained after TCBZ co-administered with IVM and MTZ (650.7 +/- 122.8 microgxh/ml). Efficacy values of 56 and 38% were observed for TCBZ alone and for the combined treatment, respectively. No statistical differences (P > 0.05) were observed in fluke counts between treated groups and untreated control, which confirm the resistant status of the Sligo isolate.

CONCLUSIONS

The presence of IVM and MTZ did not affect the disposition kinetics of TCBZ and its metabolites. Thus, the combined drug treatment did not reverse the poor efficacy of TCBZ against TCBZ-resistant F. hepatica.

Triclabendazole progress report, 2005–2009: an advancement of learning?

Triclabendazole (TCBZ) remains the drug of choice for treating infections of the liver fluke,Fasciola hepaticain livestock and has become the main drug used to treat human cases of the disease as well. Cases of resistance in livestock continue to be reported, suggesting that the problem is increasing. In order to address the problem, there is a need for better understanding of drug action. A ‘state-of-play’ review on different aspects of TCBZ activity was published by the present author in 2005. The main purpose of the current review is to assess what progress has been made in the past four years towards understanding the main aspects of drug activity, including drug pharmacokinetics and pharmacodynamics and an understanding of the mechanism(s) of resistance. Also, what advances have been made in identifying alternative compounds and using drug combinations to enhance TCBZ activity. Stemming from a number ofin vivostudies, it has become evident that fluke isolates of differing sensitivity to TCBZ differ in some of their biological parameters, and information on this interesting phenomenon will be presented. An update on the use of TCBZ for human fascioliasis is also given. The review will indicate what progress has been made, but will also highlight areas that remain inadequately understood and require greater research focus.