Intestinal secretion is a major route for parent ivermectin elimination in the rat

Biomonitoring Livestock Antiparasitic Residues: Development of Fast Mass Spectrometric Methods for the Quantification of Ivermectin, Albendazole, and their Metabolites in Sheep Plasma and Feces

Antiparasitic substances are extensively used in livestock farming against common parasitic infections. Improper utilization of these medicines often leads to the development of antiparasitic resistance and the detection of residues across the food chain, posing significant challenges to animal health, food safety, and public health. The objective of this study was to monitor antiparasitics' pharmacokinetics after the administration of ivermectin and albendazole in farm sheep. To achieve this goal, a fast LC-ESI-MS/MS method was developed and validated for the simultaneous quantification of ivermectin, albendazole, and their metabolites in sheep plasma. Concurrently, a probe electrospray tandem mass spectrometry ultrafast method was also developed for the real-time monitoring of albendazole and its metabolites in plasma. In addition, the liquid chromatography methodology was extended and validated for the detection of ivermectin in sheep feces, offering a non-invasive alternative to tissue and biofluids analysis. The detection capability values estimated for the techniques developed herein for the studied compounds and their metabolites in plasma ranged from 0.1 to 50.2 ng/mL, while the respective values for ivermectin in feces ranged between 5.0 and 26.9 ng/g. Recoveries fluctuated from 64% to 119%, proving the competence of the methods. The application of these methods in sheep samples, after the administration of the antiparasitic substances, effectively indicated the distribution of their concentrations, although in some cases, the individual animal effect seemed to interplay with the expected results. Also, these methods can contribute to the adjustment of the farm animal antiparasitic protocols, promoting the most effective utilization of the respective drugs while minimizing the risk of developing antiparasitic resistance. In a broader context, they may aid the advancement of veterinary medicine, offering practical solutions for monitoring the drug residues in farm animals and the derived products, and mitigating the risks associated with the extensive and uncontrolled utilization of antiparasitic drugs.

Impact of Ivermectin on the Gut Microbial Ecosystem

Ivermectin is a an anti-helminthic that is critical globally for both human and veterinary care. To the best of our knowledge, information available regarding the influence of ivermectin (IVM) on the gut microbiota has only been collected from diseased donors, who were treated with IVM alone or in combination with other medicines. Results thus obtained were influenced by multiple elements beyond IVM, such as disease, and other medical treatments. The research presented here investigated the impact of IVM on the gut microbial structure established in a Triple-SHIME® (simulator of the human intestinal microbial ecosystem), using fecal material from three healthy adults. The microbial communities were grown using three different culture media: standard SHIME media and SHIME media with either soluble or insoluble fiber added (control, SF, ISF). IVM introduced minor and temporary changes to the gut microbial community in terms of composition and metabolite production, as revealed by 16S rRNA amplicon sequencing analysis, flow cytometry, and GC-MS. Thus, it was concluded that IVM is not expected to induce dysbiosis or yield adverse effects if administered to healthy adults. In addition, the donor's starting community influences the relationship between IVM and the gut microbiome, and the soluble fiber component in feed could protect the gut microbiota from IVM; an increase in short-chain fatty acid production was predicted by PICRUSt2 and detected with IVM treatment.

Vitamins E and A increase the passing of the P-gp substrate ivermectin into the brain in mice

This study aimed to determine the effect of administration of oral vitamins A and E at different doses on plasma and brain concentrations of ivermectin in mice. The study was carried out on 174 Swiss Albino male mice aged 8-10 weeks. After leaving six mice for method validation, the remaining mice were randomly divided into seven groups with equal numbers of animals. Mice received ivermectin (0.2 mg/kg, subcutaneous) alone and in combination with low (vitamin A: 4000 IU/kg; vitamin E: 35 mg/kg) and high (vitamin A: 30 000 IU/kg; vitamin E: 500 mg/kg) oral doses of vitamins A and E. The plasma and brain concentrations of ivermectin were measured using high-performance liquid chromatography-fluorescence detector. We determined that high doses of vitamins A and E and their combinations increased the passing ratio of ivermectin into the brain significantly. The high-dose vitamin E and the combination of high-concentration vitamins E and A significantly increased the plasma concentration of ivermectin (P < 0.05). The high-dose vitamins E and A and their high-dose combination increased the brain concentration of ivermectin by 3, 2, and 2.7 times, respectively. This research is the first in vivo study to determine the interaction between P-gp substrates and vitamins E and A.

The investigation of the complex population-drug-drug interaction between ritonavir-boosted lopinavir and chloroquine or ivermectin using physiologically-based pharmacokinetic modeling

OBJECTIVES

Therapy failure caused by complex population-drug-drug (PDDI) interactions including CYP3A4 can be predicted using mechanistic physiologically-based pharmacokinetic (PBPK) modeling. A synergy between ritonavir-boosted lopinavir (LPVr), ivermectin, and chloroquine was suggested to improve COVID-19 treatment. This work aimed to study the PDDI of the two CYP3A4 substrates (ivermectin and chloroquine) with LPVr in mild-to-moderate COVID-19 adults, geriatrics, and pregnancy populations.

METHODS

The PDDI of LPVr with ivermectin or chloroquine was investigated. Pearson's correlations between plasma, saliva, and lung interstitial fluid (ISF) levels were evaluated. Target site (lung epithelial lining fluid [ELF]) levels of ivermectin and chloroquine were estimated.

RESULTS

Upon LPVr coadministration, while the chloroquine plasma levels were reduced by 30, 40, and 20%, the ivermectin plasma levels were increased by a minimum of 425, 234, and 453% in adults, geriatrics, and pregnancy populations, respectively. The established correlation equations can be useful in therapeutic drug monitoring (TDM) and dosing regimen optimization.

CONCLUSIONS

Neither chloroquine nor ivermectin reached therapeutic ELF levels in the presence of LPVr despite reaching toxic ivermectin plasma levels. PBPK modeling, guided with TDM in saliva, can be advantageous to evaluate the probability of reaching therapeutic ELF levels in the presence of PDDI, especially in home-treated patients.

A generic avian physiologically-based kinetic (PBK) model and its application in three bird species

Physiologically-based kinetic (PBK) models are effective tools for designing toxicological studies and conducting extrapolations to inform hazard characterization in risk assessment by filling data gaps and defining safe levels of chemicals. In the present work, a generic avian PBK model for male and female birds was developed using PK-Sim and MoBi from the Open Systems Pharmacology Suite (OSPS). The PBK model includes an ovulation model (egg development) to predict concentrations of chemicals in eggs from dietary exposure. The model was parametrized for chicken (Gallus gallus), bobwhite quail (Colinus virginianus) and mallard duck (Anas platyrhynchos) and was tested with nine chemicals for which in vivo studies were available. Time-concentration profiles of chemicals reaching tissues and egg compartment were simulated and compared to in vivo data. The overall accuracy of the PBK model predictions across the analyzed chemicals was good. Model simulations were found to be in the range of 22-79% within a 3-fold and 41-89% were within 10- fold deviation of the in vivo observed data. However, for some compounds scarcity of in-vivo data and inconsistencies between published studies allowed only a limited goodness of fit evaluation. The generic avian PBK model was developed following a "best practice" workflow describing how to build a PBK model for novel species. The credibility and reproducibility of the avian PBK models were scored by evaluation according to the available guidance documents from WHO (2010), and OECD (2021), to increase applicability, confidence and acceptance of these in silico models in chemical risk assessment.

Intestinal Excretion, Intestinal Recirculation, and Renal Tubule Reabsorption Are Underappreciated Mechanisms That Drive the Distribution and Pharmacokinetic Behavior of Small Molecule Drugs

Drug reabsorption following biliary excretion is well-known as enterohepatic recirculation (EHR). Renal tubular reabsorption (RTR) following renal excretion is also common but not easily assessed. Intestinal excretion (IE) and enteroenteric recirculation (EER) have not been recognized as common disposition mechanisms for metabolically stable and permeable drugs. IE and intestinal reabsorption (IR:EHR/EER), as well as RTR, are governed by dug concentration gradients, passive diffusion, active transport, and metabolism, and together they markedly impact disposition and pharmacokinetics (PK) of small molecule drugs. Disruption of IE, IR, or RTR through applications of active charcoal (AC), transporter knockout (KO), and transporter inhibitors can lead to changes in PK parameters. The impacts of intestinal and renal reabsorption on PK are under-appreciated. Although IE and EER/RTR can be an intrinsic drug property, there is no apparent strategy to optimize compounds based on this property. This review seeks to improve understanding and applications of IE, IR, and RTR mechanisms.

Characterization of Tissue Distribution, Catabolism, and Elimination of an Anti-Staphylococcus aureus THIOMAB Antibody-Antibiotic Conjugate in Rats

Invasive Staphylococcus aureus infection is a leading cause of infectious disease-related deaths because S. aureus survives within host phagocytic cells, from which the bacteria are not adequately eliminated using current antibiotic treatments. Anti-S. aureus THIOMAB antibody-antibiotic conjugate (TAC), an anti-S. aureus antibody conjugated with antibiotic payload dmDNA31, was designed to deliver antibiotics into phagocytes, thereby killing intracellular S. aureus Herein, we present the distribution, metabolism/catabolism, and elimination properties for this modality. The tissue distribution of TAC and the release and elimination of its payload dmDNA31 were characterized in rats using multiple approaches. Intravenous injection of unconjugated [14C]dmDNA31 to rats resulted in a rapid clearance in both systemic circulation and tissues, with biliary secretion as the major route of elimination. Six major metabolites were identified. When [14C]dmDNA31 was conjugated to an antibody as TAC and administered to rat intravenously, a sustained exposure was observed in both systemic circulation and tissues. The dmDNA31 in blood and tissues mainly remained in conjugated form after administering TAC, although minimal deconjugation of dmDNA31 from TAC was also observed. Several TAC catabolites were identified, which were mainly eliminated through the biliary-fecal route, with dmDNA31 and deacetylated dmDNA31 as the most abundant catabolites. In summary, these studies provide a comprehensive characterization of the distribution, metabolism/catabolism, and elimination properties of TAC. These data fully support further clinical development of TAC for the invasive and difficult-to-treat S. aureus infection. SIGNIFICANCE STATEMENT: The present studies provide a comprehensive investigation of the absorption, distribution, metabolism/catabolism, and elimination of the first antibody-antibiotic conjugate developed for the treatment of an infectious disease. Although many antibody-drug conjugates are in development for various disease indications, only a limited amount of absorption, distribution, metabolism/catabolism, and elimination information is available in the literature. This study demonstrates the use of radiolabeling technology to delineate the absorption, distribution, metabolism/catabolism, and elimination properties of a complex modality and help address the key questions related to clinical pharmacological studies.

Effects of verapamil on the pharmacokinetics of ivermectin in rabbits

This study was aimed to investigate the influence of verapamil-mediated inhibition of P-glycoprotein (P-gp) on the pharmacokinetics of ivermectin (IVM) given orally and subcutaneously (SC) to rabbits. Twenty New Zealand rabbits were allotted to 4 groups (n = 5) and received IVM either orally or SC (0.4 mg/kg) alone or co-administered with verapamil (2 mg/kg SC, 3 times at a 12-hr interval). Plasma, fecal, and urine samples were collected over 30 days after medication to assess IVM concentrations in these samples. No significant differences were observed in the pharmacokinetic parameters of IVM between oral and SC administrations. The area under the plasma concentration-time curve was higher (p < .05) after IVM (oral)/verapamil treatment, compared with oral IVM alone. Moreover, the time to the C_max of IVM was shorter (p < .05), whereas the elimination half-life and the mean residence time were longer (p < .05) in the presence of verapamil. The IVM/verapamil combination administered orally or SC reduced fecal IVM concentrations, compared with IVM alone. In conclusion, the significant changes by verapamil on the pharmacokinetics of IVM, likely due to the inhibition of a P-gp-mediated intestinal secretion, may change IVM's antinematodal activity.

The effect of breed, sex, and drug concentration on the pharmacokinetic profile of ivermectin in cattle

Ivermectin (IVM) is one of the most widely used antiparasitic drugs worldwide and has become the drug of choice for anthelmintic and tick treatment in beef cattle production. It is known that pharmacokinetic parameters are fundamental to the rational use of a drug and food safety and these parameters are influenced by different factors. The aim of this study was to evaluate the pharmacokinetic profile of IVM in Bos indicus, Bos taurus, and crossbreed cattle (B. indicus × B. taurus) kept under same field conditions and the possible impacts of sex and IVM formulation (1% and 3.15%). It was observed that IVM concentration was significantly affected by breed. The plasma concentrations of IVM, AUC, C_max , and t_1/2β were significantly higher in B. indicus compared to B. taurus. Crossbreed animals showed an intermediate profile between European and Indian cattle. No alteration in pharmacokinetics parameters was detected when comparing different gender. Concerning the pharmacokinetic data of IVM formulation, it was verified that T_max , AUC, and t_1/2β were higher in 3.15% IVM animals than those from 1% IVM formulation. The results clearly indicated that the IVM plasma concentrations in B. indicus were higher than that in B. taurus.

Pharmacokinetic-pharmacodynamic assessment of the ivermectin and abamectin nematodicidal interaction in cattle

In a context of nematodicidal resistance, anthelmintic combinations have emerged as a reliable pharmacological strategy to control gastrointestinal nematodes in grazing systems of livestock production. The current work evaluated the potential drug-drug interactions following the coadministration of two macrocyclic lactones (ML) ivermectin (IVM) and abamectin (ABM) to parasitized cattle using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The kinetic behavior of both compounds administered either separately or coadministered was assessed and the therapeutic response of the combination was evaluated under different resistance scenarios. In the pharmacological trial, calves received a single subcutaneous (s.c.) injection of IVM (100 μg/Kg); a single s.c. injection of ABM (100 μg/Kg) or IVM + ABM (50 μg/Kg each) administered in different injection sites to reach a final ML dose of 100 μg/Kg (Farm 1). Plasma samples were taken from those animals up to 20 days post-treatment. IVM and ABM plasma concentrations were quantified by HPLC. A parasitological trial was carried out in three farms with different status of nematodes resistance to IVM. Experimental animals received IVM (200 μg/Kg), ABM (200 μg/Kg) or IVM + ABM (100 μg/Kg each) in Farm 2, and IVM + ABM (200 μg/Kg each) in Farms 3 and 4. The anthelmintic efficacy was determined by fecal egg count reduction test (FECRT). PK analysis showed similar trends for IVM kinetic behavior after coadministration with ABM. Conversely, the ABM elimination half-life was prolonged and the systemic exposure during the elimination phase was increased in the presence of IVM. Although IVM alone failed to control Cooperia spp., the combination IVM + ABM was the only treatment that achieved an efficacy higher than 95% against resistant Cooperia spp. in all farms. In fact, when Cooperia spp. was the main genus within the nematode population and Haemonchus spp. was susceptible or slightly resistant to ML (Farms 2 and 4), the total FECR for the combination IVM + ABM was higher than 90%. Instead, when the predominant nematode genus was a highly resistant Haemonchus spp. (Farm 3), the total FECR after the combined treatment was as low as the single treatments. Therefore, the rational use of these pharmacological tools should be mainly based on the knowledge of the epidemiology and the nematode susceptibility status in each cattle farm.

Ivermectin environmental impact: Excretion profile in sheep and phytotoxic effect in Sinapis alba

Ivermectin (IVM), a macrocylic lactone from the avermectin family, is a potent broad-spectrum anthelmintic drug widely used in veterinary as well as human medicine. Although the health benefits of IVM treatment are particularly important, this drug also represents an environmental pollutant with potentially negative effects on many non-target species. To evaluate the ecotoxicological risk of IVM administration to livestock, information evaluating achievable environment-reaching concentration is needed. Therefore, the present study was designed to determine the excretion profile of subcutaneously administered IVM in sheep. The standard recommended dose of IVM (0.2 mg kg^-1 b.w.) was used. UHPLC/MS/MS was used for the analysis of IVM faecal concentration. In addition, the effect of IVM on seed germination and early roots growth of white mustard (Sinapis alba L.) was evaluated in order to estimate the potential phytotoxic effect of IVM. Based on the obtained results, the parameters of IVM pharmacokinetics (maximum concentration (c_max), time to achieve maximum concentration (t_max), mean residence time (MRT), area under the curve (AUC)) were calculated. IVM elimination in sheep was slow, but faster than the elimination reported previously in cattle. Great interindividual differences were also observed. A two-peak profile of concentration curves indicate the importance of the active efflux of IVM via enterocytes. A "seed germination and early roots growth" test revealed significant IVM phytotoxicity (20% inhibition of root growth) even at 50 nM concentration, a level which may be found in the environment. This newly demonstrated phytotoxicity of IVM together with its well-known toxicity to invertebrates should be taken into account, and thus animals treated with IVM should not be kept in pastures, especially not in sites with high ecological value.

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.

A sensitive and selective LC-MS/MS method for quantitation of ivermectin in human, mouse and monkey plasma: clinical validation

Aim: A sensitive and selective LC-MS/MS method was validated for quantitation of ivermectin (IVM) in plasma. Method: The IVM was extracted from plasma using solid-phase extraction with C-18 cartridges. Separation of analytes was achieved on an ACE C18 column with isocratic elution using 0.1% acetic acid and methanol: acetonitrile (1:1, v/v) as mobile phase. The IVM was quantitated using electrospray ionization operating in negative multiple reaction monitoring mode. Results: The MS/MS response was linear over the concentration range from 0.1-1000 ng/ml. The method for human plasma was validated as per US FDA guidelines. The LC-MS/MS method is sensitive, reproducible, has easy sample preparation and is suitable for IVM quantitation in clinical samples.

High concentrations of perfluorooctane sulfonate in mucus of tiger puffer fish Takifugu rubripes: a laboratory exposure study

Distribution of perfluorooctane sulfonate (PFOS) was investigated in tissues (plasma, blood clot, mucus, skin, liver, muscle, and gonad) of tiger puffer fish Takifugu rubripes. A single dose of PFOS was intraperitoneally injected at 0.1 mg/kg body weight with samples taken over a 14-day period. The highest concentration of PFOS was found in the plasma, 861 ng/mL at 14 days, followed by the mucus, liver, blood clot, gonads, muscles, and skin of fish. A gradual upward trend in PFOS concentration was observed in the mucus and liver whereas there was no change in the plasma, blood clot, gonad, muscle, and skin after the initial increase in PFOS concentrations following injection. No significant trend for estimated total PFOS content in whole body was observed during the experimental period. Relatively high concentrations of PFOS (690 ng/g ww after 14 days) were detected in body surface mucus that continuously oozes from the skin. These results may suggest that mucus is one of the elimination pathways of PFOS in tiger puffer fish.

P-glycoproteins play a role in ivermectin resistance in cyathostomins

Anthelmintic resistance is a global problem that threatens sustainable control of the equine gastrointestinal cyathostomins (Phylum Nematoda; Superfamily Strongyloidea). Of the three novel anthelmintic classes that have reached the veterinary market in the last decade, none are currently licenced in horses, hence current control regimens focus on prolonging the useful lifespan of licenced anthelmintics. This approach would be facilitated by knowledge of the resistance mechanisms to the most widely used anthelmintics, the macrocyclic lactones (ML). There are no data regarding resistance mechanisms to MLs in cyathostomins, although in other parasitic nematodes, the ABC transporters, P-glycoproteins (P-gps), have been implicated in playing an important role. Here, we tested the hypothesis that P-gps are, at least in part, responsible for reduced sensitivity to the ML ivermectin (IVM) in cyathostomins; first, by measuring transcript levels of pgp-9 in IVM resistant versus IVM sensitive third stage larvae (L3) pre-and post-IVM exposure in vitro. We then tested the effect of a range of P-gp inhibitors on the effect of IVM against the same populations of L3 using the in vitro larval development test (LDT) and larval migration inhibition test (LMIT). We demonstrated that, not only was pgp-9 transcription significantly increased in IVM resistant compared to IVM sensitive L3 after anthelmintic exposure (p < 0.001), but inhibition of P-gp activity significantly increased sensitivity of the larvae to IVM in vitro, an effect only observed in the IVM resistant larvae in the LMIT. These data strongly implicate a role for P-gps in IVM resistance in cyathostomins. Importantly, this raises the possibility that P-gp inhibitor-IVM combination treatments might be used in vivo to increase the effectiveness of IVM against cyathostomins in Equidae.

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Pgp-9 transcript levels were higher in ivermectin resistant versus susceptible cyathostomin populations.

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P-gp inhibitors increased ivermectin effect against cyathostomins in vitro.

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P-gp activity may play a role in ivermectin resistance in cyathostomins.

Rate-Determining and Rate-Limiting Steps in the Clearance and Excretion of a Potent and Selective p21-Activated Kinase Inhibitor: A Case Study of Rapid Hepatic Uptake and Slow Elimination in Rat

BACKGROUND

Significant under-prediction of in vivo clearance in rat was observed for a potent p21-activated kinase (PAK1) inhibitor, GNE1.

OBJECTIVE

Rate-determining (rapid uptake) and rate-limiting (slow excretion) steps in systemic clearance and elimination of GNE1, respectively, were evaluated to better understand the cause of the in vitro-in vivo (IVIV) disconnect.

METHODS

A series of in vivo, ex vivo, and in vitro experiments were carried out: 1) the role of organic cation transporters (Oct or Slc22a) was investigated in transporter knock-out and wild-type animals with or without 1-aminobenzotriazole (ABT) pretreatment; 2) the concentration-dependent hepatic extraction ratio was determined in isolated perfused rat liver; and 3) excreta were collected from both bile duct cannulated and non-cannulated rats after intravenous injection.

RESULTS

After intravenous dosing, the rate-determining step in clearance was found to be mediated by the active uptake transporter, Oct1. In cannulated rats, biliary and renal clearance of GNE1 accounted for only approximately 14 and 16% of the total clearance, respectively. N-acetylation, an important metabolic pathway, accounted for only about 10% of the total dose. In non-cannulated rats, the majority of the dose was recovered in feces as unchanged parent (up to 91%) overnight following intravenous administration.

CONCLUSION

Because the clearance of GNE1 is mediated through uptake transporters rather than metabolism, the extrahepatic expression of Oct1 in kidney and intestine in rat likely plays an important role in the IVIV disconnect in hepatic clearance prediction. The slow process of intestinal secretion is the rate-limiting step for in vivo clearance of GNE1.

Ivermectin Pharmacokinetics, Metabolism, and Tissue/Egg Residue Profiles in Laying Hens

The goals were to determine the ivermectin (IVM) plasma pharmacokinetics, tissue and egg residue profiles, and in vitro metabolism in laying hens. Experiments conducted were (1) 8 hens were intravenously treated with IVM and blood samples taken; (2) 88 hens were treated with IVM administered daily in water (5 days) (40 were kept and their daily eggs collected; 48 were sacrificed in groups (n = 8) at different times and tissue samples taken and analyzed); (3) IVM biotransformation was studied in liver microsomes. Pharmacokinetic parameters were AUC = 85.1 ng·day/mL, Vdss = 4.43 L/kg, and T1/2el = 1.73 days. Low IVM tissue residues were quantified with the highest measured in liver and skin+fat. IVM residues were not found in egg white, but significant amounts were quantified in yolk. Residues measured in eggs were greater than some MRL values, suggesting that a withdrawal period would be necessary for eggs after IVM use in laying hens.

Ivermectin exposure leads to up-regulation of detoxification genes in vitro and in vivo in mice

The biodisposition of the antiparasitic drug ivermectin in host and parasite is decisive for its efficacy and strongly depends on the efflux by ATP-Binding Cassette (ABC) transporters and on its biotransformation by cytochromes P450. The purpose of this study was to evaluate, in vitro and in vivo, the ivermectin ability in modulating the expression of the most important genes involved in drug detoxification. Gene expression of ABC transporters and cytochromes was evaluated by RT-qPCR in murine hepatic and intestinal cell lines exposed to increasing ivermectin doses, and in liver and intestine of mice orally administered with single or repeated therapeutic doses of ivermectin (0.2 mg/kg). Plasma, brain, liver and intestinal concentrations of ivermectin and its main metabolite were measured by HPLC in ivermectin-treated mice. In hepatocyte cell line, ivermectin up-regulated expression of Abcb1a, Abcb1b, Abcc2, Cyp1a1, Cyp1a2, Cyp2b10; while Abcb1a, Abcb1b, Abcg2, Cyp1a1, Cyp1a2, Cyp2b10 and Cyp3a11 levels were induced in intestinal cell line. In mice, repeated administration of ivermectin induced the expression of Abcb1a, Abcc2, Cyp1a1 and Cyp2b10 in intestine while only Cyp3a11 was induced in liver. Compared with single administration, repeated ivermectin administration lowered plasma, liver and intestine drug concentration, while increasing main metabolite content in plasma and intestine. These findings can be regarded as a warning that repeated ivermectin exposure is able to induce detoxification systems in mammals that may lead to subtherapeutic drug concentration. This may also be an important consideration in the assessment of drug-drug interaction and toxicity for other ABC transporters and CYP450s substrates.

Human disposition, metabolism and excretion of etamicastat, a reversible, peripherally selective dopamine β-hydroxylase inhibitor

AIMS

Etamicastat is a reversible dopamine-β-hydroxylase inhibitor that decreases noradrenaline levels in sympathetically innervated tissues and slows down sympathetic nervous system drive. In this study, the disposition, metabolism and excretion of etamicastat were evaluated following [(14)C]-etamicastat dosing.

METHODS

Healthy Caucasian males (n = 4) were enrolled in this single-dose, open-label study. Subjects were administered 600 mg of unlabelled etamicastat and 98 µCi weighing 0.623 mg [(14)C]-etamicastat. Blood samples, urine and faeces were collected to characterize the disposition, excretion and metabolites of etamicastat.

RESULTS

Eleven days after administration, 94.0% of the administered radioactivity had been excreted; 33.3 and 58.5% of the administered dose was found in the faeces and urine, respectively. Renal excretion of unchanged etamicastat and its N-acetylated metabolite (BIA 5-961) accounted for 20.0 and 10.7% of the dose, respectively. Etamicastat and BIA 5-961 accounted for most of the circulating radioactivity, with a BIA 5-961/etamicastat ratio that was highly variable both for the maximal plasma concentration (19.68-226.28%) and for the area under the plasma concentration-time curve from time zero to the last sampling time at which the concentration was above the limit of quantification (15.82- 281.71%). Alongside N-acetylation, metabolism of etamicastat also occurs through oxidative deamination of the aminoethyl moiety, alkyl oxidation, desulfation and glucuronidation.

CONCLUSIONS

Etamicastat is rapidly absorbed, primarily excreted via urine, and its biotransformation occurs mainly via N-acetylation (N-acetyltransferase type 2), although glucuronidation, oxidation, oxidative deamination and desulfation also take place.

Intestinal drug transport: ex vivo evaluation of the interactions between ABC transporters and anthelmintic molecules

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.

Accumulation of monepantel and its sulphone derivative in tissues of nematode location in sheep: pharmacokinetic support to its excellent nematodicidal activity

The amino-acetonitrile derivatives (AADs) are a new class of anthelmintic molecules active against a wide range of sheep gastrointestinal (GI) nematodes including those that are resistant to other anthelmintic families. The plasma disposition of monepantel (MNP) has been previously characterized in sheep. However, information on drug concentration profiles attained at tissues of parasite location is necessary to fully understand the pharmacological action of this novel compound. The current work aimed to study the relationship between the concentrations of MNP parent drug and its main metabolite monepantel sulphone (MNPSO₂), measured in the bloodstream and in different GI tissues of parasite location in sheep. Twenty two (22) uninfected healthy Romney Marsh lambs received MNP (Zolvix, Novartis Animal Health) orally administered at 2.5 mg/kg. Blood samples were collected from six animals between 0 and 14 days post-treatment to characterize the drug/metabolite plasma disposition kinetics. Additionally, 16 lambs were sacrificed at 8, 24, 48 and 96 h post-administration to assess the drug concentrations in the GI fluid contents and tissues. MNP and MNPSO₂ concentrations were determined by HPLC. MNP parent compound was rapidly oxidized into MNPSO₂. MNP systemic availability was significantly lower than that observed for MNPSO₂. The peak plasma concentrations were 15.1 (MNP) and 61.4 ng/ml (MNPSO₂). The MNPSO₂ to MNP plasma concentration profile ratio (values expressed in AUC) reached a value of 12. Markedly higher concentrations of MNP and MNPSO₂ were measured in both abomasal and duodenal fluid contents, and mucosal tissues compared to those recovered from the bloodstream. A great MNP availability was measured in the abomasal content with concentration values ranging between 2000 and 4000 ng/g during the first 48 h post-treatment. Interestingly, the metabolite MNPSO₂ was also recovered in abomasal content but its concentrations were significantly lower compared to MNP. The parent drug and its sulphone metabolite were detected in the different segments of the sheep intestine. MNPSO₂ concentrations in the different intestine sections sampled were significantly higher compared to those measured in the abomasum. Although MNP is metabolized to MNPSO₂ in the liver, the large concentrations of both anthelmintically active molecules recovered during the first 48 h post-treatment from the abomasum and small intestine may greatly contribute to the well-established pharmacological activity of MNP against GI nematodes.

Intestinal drug transporters: an overview

The importance of drug transporters as one of the determinants of pharmacokinetics has become increasingly evident. While much research has been conducted focusing the role of drug transporters in the liver and kidney less is known about the importance of uptake and efflux transporters identified in the intestine. Over the past years the effects of intestinal transporters have been studied using in vivo models, in situ organ perfusions, in vitro tissue preparations and cell lines. This review aims to describe up to date findings regarding the importance of intestinal transporters on drug absorption and bioavailability, highlighting areas in need of further research. Wu and Benet proposed a Biopharmaceutics Drug Disposition Classification System (BDDCS) that allows the prediction of transporter effects on the drug disposition of orally administered drugs. This review also discusses BDDCS predictions with respect to the role of intestinal transporters and intestinal transporter-metabolizing enzyme interplay on oral drug pharmacokinetics.

Comparative tissue pharmacokinetics and efficacy of moxidectin, abamectin and ivermectin in lambs infected with resistant nematodes: Impact of drug treatments on parasite P-glycoprotein expression

The high level of resistance to the macrocyclic lactones has encouraged the search for strategies to optimize their potential as antiparasitic agents. There is a need for pharmaco-parasitological studies addressing the kinetic-dynamic differences between various macrocyclic lactones under standardized in vivo conditions. The current work evaluated the relationship among systemic drug exposure, target tissue availabilities and the pattern of drug accumulation within resistant Haemonchus contortus for moxidectin, abamectin and ivermectin. Drug concentrations in plasma, target tissues and parasites were measured by high performance liquid chromatography. Additionally, the efficacy of the three molecules was evaluated in lambs infected with resistant nematodes by classical parasitological methods. Furthermore, the comparative determination of the level of expression of P-glycoprotein (P-gp2) in H. contortus recovered from lambs treated with each drug was performed by real time PCR. A longer persistence of moxidectin (P < 0.05) concentrations in plasma was observed. The concentrations of the three compounds in the mucosal tissue and digestive contents were significant higher than those measured in plasma. Drug concentrations were in a range between 452 ng/g (0.5 day post-treatment) and 32 ng/g (2 days post-treatment) in the gastrointestinal (GI) contents (abomasal and intestinal). Concentrations of the three compounds in H. contortus were in a similar range to those observed in the abomasal contents (positive correlation P = 0.0002). Lower moxidectin concentrations were recovered within adult H. contortus compared to abamectin and ivermectin at day 2 post-treatment. However, the efficacy against H. contortus was 20.1% (ivermectin), 39.7% (abamectin) and 89.6% (moxidectin). Only the ivermectin treatment induced an enhancement on the expression of P-gp2 in the recovered adult H. contortus, reaching higher values at 12 and 24 h post-administration compared to control (untreated) worms. This comparative pharmacological evaluation of three of the most used macrocyclic lactones compounds provides new insights into the action of these drugs.

Moxidectin and the avermectins: Consanguinity but not identity

The avermectins and milbemycins contain a common macrocyclic lactone (ML) ring, but are fermentation products of different organisms. The principal structural difference is that avermectins have sugar groups at C13 of the macrocyclic ring, whereas the milbemycins are protonated at C13. Moxidectin (MOX), belonging to the milbemycin family, has other differences, including a methoxime at C23. The avermectins and MOX have broad-spectrum activity against nematodes and arthropods. They have similar but not identical, spectral ranges of activity and some avermectins and MOX have diverse formulations for great user flexibility. The longer half-life of MOX and its safety profile, allow MOX to be used in long-acting formulations. Some important differences between MOX and avermectins in interaction with various invertebrate ligand-gated ion channels are known and could be the basis of different efficacy and safety profiles. Modelling of IVM interaction with glutamate-gated ion channels suggest different interactions will occur with MOX. Similarly, profound differences between MOX and the avermectins are seen in interactions with ABC transporters in mammals and nematodes. These differences are important for pharmacokinetics, toxicity in animals with defective transporter expression, and probable mechanisms of resistance. Resistance to the avermectins has become widespread in parasites of some hosts and MOX resistance also exists and is increasing. There is some degree of cross-resistance between the avermectins and MOX, but avermectin resistance and MOX resistance are not identical. In many cases when resistance to avermectins is noticed, MOX produces a higher efficacy and quite often is fully effective at recommended dose rates. These similarities and differences should be appreciated for optimal decisions about parasite control, delaying, managing or reversing resistances, and also for appropriate anthelmintic combination.

Macrocyclic Lactone Endectocides

The macrocyclic lactone endectocides such as ivermectin, abamectin, selamectin and moxidectin have revolutionized the treatment of parasitic diseases in animals, being active against internal and external parasites. Ivermectin was introduced into veterinary medicine in the 1980s and since that time a number of related compounds have been introduced. In the treatment of internal parasites they complement the use of levamisole and the benzimidazoles, but in recent years they have found utility in treating external insect parasites. These agents show very low levels of toxicity under most circumstances. However, they are neurotoxic particularly in subpopulations of animals with mutations in the MDR1 gene. Toxicity may be also seen during off-label use, possibly because the doses used have been extrapolated from use in other animals. Regardless of these considerations, the macrocyclic lactone endectocides are extremely effective and safe drugs in the treatment of parasitic diseases of animals.

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.

Pharmacokinetic interaction of the antiparasitic agents ivermectin and spinosad in dogs

Neurological side effects consistent with ivermectin toxicity have been observed in dogs when high doses of the common heartworm prevention agent ivermectin are coadministered with spinosad, an oral flea prevention agent. Based on numerous reports implicating the role of the ATP-binding cassette drug transporter P-glycoprotein (P-gp) in ivermectin efflux in dogs, an in vivo study was conducted to determine whether ivermectin toxicity results from a pharmacokinetic interaction with spinosad. Beagle dogs were randomized to three groups treated orally in parallel: Treatment group 1 (T01) received ivermectin (60 μg/kg), treatment group 2 (T02) received spinosad (30 mg/kg), and treatment group 3 (T03) received both ivermectin and spinosad. Whereas spinosad pharmacokinetics were unchanged in the presence of ivermectin, ivermectin plasma pharmacokinetics revealed a statistically significant increase in the area under the curve (3.6-fold over the control) when ivermectin was coadministered with spinosad. The majority of the interaction is proposed to result from inhibition of intestinal and/or hepatic P-gp-mediated secretory pathways of ivermectin. Furthermore, in vitro Transwell experiments with a human multidrug resistance 1-transfected Madin-Darby canine kidney II cell line showed polarized efflux at concentrations ≤ 2 μM, indicating that spinosad is a high-affinity substrate of P-gp. In addition, spinosad was a strong inhibitor of the P-gp transport of digoxin, calcein acetoxymethyl ester (IC(50) = 3.2 μM), and ivermectin (IC(50) = 2.3 μM). The findings suggest that spinosad, acting as a P-gp inhibitor, increases the risk of ivermectin neurotoxicity by inhibiting secretion of ivermectin to increase systemic drug levels and by inhibiting P-gp at the blood-brain barrier.

The influence of gastrointestinal parasitism on fecal elimination of doramectin, in lambs

A study was done to investigate the effect of parasitism on patterns of doramectin (DRM) fecal elimination in lambs. Fourteen Suffolk Down parasitized lambs (26.9 ± 1.5 kg body weight: bw) were purposely selected for the study. Seven pairs of lambs were allocated into two experimental groups. Group I (non-parasitized) was pre-treated with 3 repeated administrations of 5mg/kg bw of fenbendazole to maintain a non-parasitized condition. In Group II (parasitized), the lambs did not receive any anthelmintic treatment. After 85 d of the pre-treatment period, both groups were treated with a subcutaneous injection of 200 μg/kg bw of DRM. Fecal samples were collected at different times between -85 d before and 60 d after the DRM treatment, for both parasitological and chromatographic analysis. Samples were analyzed by high-performance liquid chromatography (HPLC) with fluorescence detection. Data of DRM concentrations were expressed as wet weight. A non-linear pharmacokinetic analysis was performed and results were compared using the Mann Whitney test. Fecal maximum concentrations (C(max)) of DRM were 1.37 ± 0.19 μg/g (parasitized group) and 0.86 ± 0.15 μg/g (non-parasitized group) observed at the time of the maximum concentration (T(max)) of 2.1 ± 0.4 and 3.1 ± 0.3d, respectively. Differences in C(max) values were significant (P<0.05). The accumulated elimination of DRM in feces, expressed as the percentage of DRM total dose, was 67.1% in the parasitized group, whereas in the non-parasitized group it was 56.5%. Our results showed that gastrointestinal parasitic diseases can modify the patterns of DRM fecal elimination, when the drug is administered by subcutaneous route in lambs.

Pretreatment with the inducers rifampicin and phenobarbital alters ivermectin gastrointestinal disposition

The goal of the study was to evaluate the effects of rifampicin (RFP) and phenobarbital (PBT) on the plasma and gastrointestinal disposition kinetics of ivermectin (IVM) subcutaneously administered to Wistar rats. Fifty seven rats were used. Animals in Group I were the noninduced (control) group. Those in Groups II and III received a treatment with RFP (160 mg/day) and PBT (35 mg/day), respectively, both given orally during eight consecutive days as induction regimen. The IVM pharmacokinetic study was started 24 h after the RFP and PBT last administration. Animals received IVM (200 microg/kg) by subcutaneous injection. Rats were sacrificed between 6 h and 3 days after IVM administration. Blood and samples of liver tissue, intestinal wall and luminal content of jejunum were collected from each animal. IVM concentrations were measured by high performance liquid chromatography. IVM disposition kinetics in plasma and tissues was significantly modified by the PBT treatment, but not by RFP. Despite the enhanced CYP3A activity observed after the pretreatment with RPF and PBT, there were no marked changes on the percentages of IVM metabolites recovered from the bloodstream in induced and noninduced animals. An enhanced P-glycoprotein-mediated intestinal transport activity in pretreated animals (particularly in PBT pretreated rats) may explain the drastic changes observed on IVM disposition.

Effect of ivermectin on the liver of gilthead sea bream Sparus aurata: a proteomic approach

Gilthead sea bream Sparus aurata is the most commercialized Mediterranean aquacultured fish species. Ivermectin has recently (experimentally) started to be used to control ectoparasitic infestations in Mediterranean cultured marine fish. The potential hepatotoxicity of ivermectin was investigated in gilthead sea bream juveniles (35g) following oral administration at the recommended dose of 0.2 mgkg(-1) fish for 10d. Difference Gel Electrophoresis Technology (DIGE) was used to study the effect of this treatment in gilthead sea bream liver protein profile under routine culture conditions. The 2D-DIGE protein maps obtained were analyzed using the DeCyder 6.5 software. The results obtained showed significant changes in the expression of 36 proteins respect to the control group. Among these proteins, six increased in abundance, and 30 decreased. Spot showing differential expression respect to the control were analyzed by mass spectrometry and database search, which resulted in three positive identifications corresponding to hepatic proteins involved in lipid metabolism (apoA-I), oxidative stress responses and energy generation (beta-globin, ATP synthase subunit beta). These proteins have not been previously associated to invermectin effect.

Interference with P-glycoprotein improves ivermectin activity against adult resistant nematodes in sheep

The in vivo co-administration of ivermectin (IVM) with P-glycoprotein (P-gp) modulator agents has been shown to enhance its systemic availability. However, there is no sufficient evidence on the impact that this type of drug-drug interaction may have on the in vivo efficacy against resistant nematodes in ruminant species. The current work reports on the effects of loperamide (LPM), a P-gp modulating agent, on both IVM kinetic behaviour and anthelmintic activity in infected lambs. Eighteen (18) lambs naturally infected with IVM-resistant gastrointestinal nematodes were allocated into three (3) experimental groups. Group A remained as untreated control. Animals in Groups B and C received IVM (200mug/kg, subcutaneously) either alone or co-administered with LPM (0.2 mg/kg, twice every 12h), respectively. Individual faecal samples were collected from experimental animals at days -1 and 14 post-treatment to perform the faecal eggs count reduction test (FECRT). Blood samples were collected between 0 and 14 days post-treatment and IVM plasma concentrations were determined by HPLC. Additionally, at day 14 post-treatment, lambs from all experimental groups were sacrificed and adult gastrointestinal nematode counts were performed. FECRT values increased from 78.6 (IVM alone) to 96% (IVM+LPM). Haemonchus contortus was highly resistant to IVM. The IVM alone treatment was completely ineffective (0% efficacy) against adult H. contortus. This efficacy value increased up to 72.5% in the presence of LPM. The efficacy against Trichostrongylus colubriformis increased from 77.9% (IVM alone) to 96.3% (IVM+LPM). The described favorable tendency towards improved anthelmintic efficacy was in agreement with the enhanced IVM plasma availability (P<0.05) and prolonged elimination half-life (P<0.05) induced by LPM in infected lambs. A LPM-induced P-gp modulation increases IVM systemic exposure in the host but also it may reduce P-gp efflux transport over-expressed in target resistant nematodes.

Role of P-glycoprotein in the disposition of macrocyclic lactones: A comparison between ivermectin, eprinomectin, and moxidectin in mice

Macrocyclic lactones (MLs) are lipophilic anthelmintics and substrates for P-glycoprotein (P-gp), an ATP-binding cassette transporter involved in drug efflux out of both host and parasites. To evaluate the contribution of P-gp to the in vivo kinetic disposition of MLs, the plasma kinetics, brain concentration, and intestinal excretion of three structurally different MLs (ivermectin, eprinomectin, and moxidectin) were compared in wild-type and P-gp-deficient [mdr1ab(-/-)] mice. Each drug (0.2 mg/kg) was administered orally, intravenously, or subcutaneously to the mice. Plasma, brain, and intestinal tissue concentrations were measured by high-performance liquid chromatography. The intestinal excretion rate after intravenous administration was determined at different levels of the small intestine by using an in situ intestinal perfusion model. P-gp deficiency led to a significant increase in the area under the plasma concentration-time curve (AUC) of ivermectin (1.5-fold) and eprinomectin (3.3-fold), whereas the moxidectin AUC was unchanged. Ivermectin and to a greater extent eprinomectin were both excreted by the intestine via a P-gp-dependent pathway, whereas moxidectin excretion was weaker and mostly P-gp-independent. The three drugs accumulated in the brains of the mdr1ab(-/-) mice, but eprinomectin concentrations were significantly lower. We concluded that eprinomectin disposition in mice is controlled mainly by P-gp efflux, more so than that of ivermectin, whereas moxidectin disposition appears to be mostly P-gp-independent. Given that eprinomectin and ivermectin have higher affinity for P-gp than moxidectin, these findings demonstrated that the relative affinity of MLs for P-gp could be predictive of the in vivo kinetic behavior of these drugs.

Loperamide modifies the tissue disposition kinetics of ivermectin in rats

Ivermectin (IVM) is a broad-spectrum antiparasitic drug extensively used in human and veterinary medicine that is largely excreted in bile and faeces. Loperamide (LPM) is an opioid derivative that reduces gastrointestinal secretions and motility. Both IVM and LPM have been reported to act as P-glycoprotein substrates (P-GP). The goal of the present work was to study the LPM-induced modifications to the pattern of tissue distribution for IVM. Thirty-six Wistar male rats were randomly allocated to two groups (n = 18) and treated subcutaneously with IVM alone or co-administered with LPM. Rats were killed at different times post-treatment and samples (blood and tissues) were collected and analyzed by HPLC. The presence of LPM induced a marked enhancement in the IVM plasma concentrations, resulting in a significantly higher area under concentration time curve (AUC) value (P &lt; 0.01) than that obtained after the administration of IVM alone. Significantly higher IVM availabilities in the liver tissue and small intestine wall (P &lt; 0.05) were obtained in the presence of LPM. There were no statistically significant differences in drug availability in the large intestinal wall after both treatments. However, LPM induced a marked decrease in the amount of IVM recovered in the large intestinal lumen content. The ratio between IVM concentrations in the large intestinal luminal content and plasma at day 1 post-treatment was 4.64-fold higher in the absence of LPM. The delayed intestinal transit time caused by LPM accounting for an extended plasma–intestine recycling time, and a potential competition between IVM and LPM for the P-GP-mediated bile–intestinal secretion processes, may account for the enhanced IVM systemic availability reported in the current study.