Influence of Dyslipidemia on Moxidectin Distribution in Plasma Lipoproteins and on its Pharmacokinetics

Free drug percentage of moxidectin declines with increasing concentrations in the serum of marsupials

Moxidectin (MOX) is a macrocyclic lactone used to eliminate endo and ectoparasites in many mammalian species. It is notably the active ingredient of the anti-parasitic drug Cydectin®, manufactured by Virbac, and is frequently used to treat sarcoptic mange in Australian wildlife. Protein binding plays a significant role in the efficacy of a drug, as the unbound/free drug in plasma ultimately reflects the pharmacologically relevant concentration. This study aimed to investigate the free drug percentage of Moxidectin after in vitro spiking into the sera of four sarcoptic mange-susceptible Australian wildlife species; the koala (Phascolarctos cinereus), the bare-nosed wombat (Vombatus ursinus), the eastern grey kangaroo (Macropus giganteus), and the mountain brushtail possum (Trichosurus cunninghami). Three concentration points of MOX were tested for each individual: 20 pg/μL, 100 pg/μL and 500 pg/μL. Serum from five individuals of each species underwent an equilibrium dialysis followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). The results showed an atypical concentration dependent binding across all species, where free drug percentage decreased as MOX concentration increased. In addition, wombats showed significantly lower free drug levels. These findings call for further research into the mechanisms of moxidectin protein binding to help understand MOX pharmacokinetics in marsupials.

Pharmacokinetics of subcutaneously administered doramectin in alpacas

The objective of this research was to evaluate comparative pharmacokinetics of doramectin in alpacas, after subcutaneous administration of 0.2 mg/kg dose. Six healthy adult alpacas, mean age of 5 years ± 1, (three female and three gelded males) of mean bodyweight of 62 kg ± 16 kg with an average body condition scored 2.8 ± 1 out of five, were used in this study. Serial blood samples were collected from the jugular vein before the administration until day 21 afterwards to establish the pharmacokinetics of doramectin after its subcutaneous administration at 0.2 mg/kg dose. The blood samples were analysed using high-performance liquid chromatography (HPLC), fluorescence detection method with precolumn derivatisation, validated for alpacas. The pharmacokinetic parameters were calculated using a noncompartmental model, and results showed Cmax (6.05 ± 5.34 ng/ml), Tmax (3.83 ± 2.48 days), AUC (62.12 ± 18.86 ng/ml × d), terminal half-life (6.2 ± 4.9 days) and MRT (11.56 ± 4.43 days). The results of this study showed that the Cmax and AUC were much lower than in cattle and sheep at the same dosage. Tmax remained similar to cattle and sheep. This study presents valuable information about pharmacokinetics of doramectin in alpacas, which can be utilised in its future efficacy studies.

Pharmacokinetics of moxidectin in alpacas following administration of an oral or subcutaneous formulation

The purpose of this study was to evaluate the pharmacokinetics of moxidectin in alpacas after single subcutaneous injection of a non-aqueous formulation or oral administration of an aqueous drench at 0.2 mg∗kg(-1). Plasma moxidectin concentrations were measured with reverse phase HPLC, and data analyzed using non-compartmental methods. Half-life was longer (p=0.02) after subcutaneous administration than oral (292+/-170 vs 33+/-39 h). The area under the concentration-time curve was greater (p=0.04) following subcutaneous administration (1484.8+/-1049.5 h∗ng∗ml(-1)) than oral (157.6+/-85.9 h∗ng∗ml(-1)). The peak concentration (Cmax) was higher and the after subcutaneous administration, but the difference was not statistically significant (p=0.18). The relative bioavailability of the oral moxidectin to the subcutaneous moxidectin was 11%. The data suggest a higher relative bioavailability following subcutaneous compared to oral administration. Further studies are needed to determine the therapeutic concentrations of moxidectin in alpacas.

The role of molecular physicochemical properties and apolipoproteins in association of drugs with triglyceride-rich lipoproteins: in-silico prediction of uptake by chylomicrons

Objectives

The uptake of drugs by chylomicrons is a key element in both intestinal lymphatic transport and postprandial alterations in the disposition profile of lipophilic drugs. The aim of this article was to elucidate the factors that affect this phenomenon.

Methods

The degree of association of 22 model lipophilic molecules with rat chylomicrons was assessed and correlated in silico with calculated physicochemical properties. The in-silico model was then validated using an external set of molecules. The uptake by chylomicrons was also compared to the association with a marketed artificial emulsion.

Key findings

The most important physicochemical property that affects the affinity to chylomicrons was found to be LogD7.4; however, a multiparameter model was required to describe properly the uptake process. The in-silico model (R2Y = 0.91, R2X = 0.91 and Q2 = 0.82) that was created using a combination of eight molecular descriptors enabled successful prediction of the affinity of the external set of molecules to chylomicrons. The association with the artificial emulsion was statistically different from the uptake by chylomicrons for four (out of nine) molecules.

Conclusions

The association of drugs with chylomicrons is a complex process, which involves the lipophilic core as well as surface apoproteins. The in-silico model based on multiple physicochemical properties of the drugs is able to predict successfully the degree of association with chylomicrons.

Impact of cholesterol on ABC and SLC transporters expression and function and its role in disposition variability to lipid-lowering drugs

This report focuses on the effects of cholesterol on the expression and function of the ATP-binding cassette (ABCB1, ABCG2 and ABCC2) and solute-linked carrier (SLCO1B1 and SLCO2B1) drug transporters with a particular focus on the potential impact of cholesterol on lipid-lowering drug disposition. Statins are the most active agents in the treatment of hypercholesterolemia. However, considerable interindividual variation exists in the response to statin therapy. Therefore, it would be huge progress if factors were identified that reliably differentiate between responders and nonresponders. Many studies have suggested that plasma lipid concentrations can affect drug disposition of compounds, such as ciclosporin and amphotericin B. Both compounds are able to affect the expression and function of ABC transporters. Although still speculative, these effects might be owing to the regulation of drug transporters by plasma cholesterol levels. Studies with normo- and hyper-cholesterolemic individuals, before and after atorvastatin treatment, have demonstrated that plasma cholesterol levels are correlated with drug transporter expression, as well as being related to atorvastatin’s cholesterol-lowering effect. The mechanism influencing the correlation between cholesterol levels and the expression and function of drug transporters remains unclear. Some studies provide strong evidence that nuclear receptors, such as the pregnane X receptor and the constitutive androstane receptor, mediate this effect. In the near future, pharmacogenomic studies with individuals in a pathological state should be performed in order to identify whether high plasma cholesterol levels might be a factor contributing to interindividual oral drug bioavailability.

The effect of plasma lipids on the pharmacokinetics of chlorpyrifos and the impact on interpretation of blood biomonitoring data

Lipophilic molecules, like chlorpyrifos (CPF), present a special problem for interpretation of biomonitoring data because both the environmental dose of CPF and the physiological (pregnancy, diet, etc.) or pathological levels of blood lipids will affect the concentrations of CPF measured in blood. The objective of this study was to investigate the distribution of CPF between plasma and tissues when lipid levels are altered in late pregnancy. CPF was sequestered more in the low-density lipid fraction of the blood during the late stages of gestation in the rat and returned to nonpregnant patterns in the dam after birth. Plasma partitioning of CPF increased with increases in plasma lipid levels and the increased partitioning of CPF into plasma lipids resulted in less CPF in other tissue compartments. Gavage dosing with corn oil also increased plasma lipids that led to a moderate increase of CPF partitioning into the plasma. To mechanistically investigate the potential pharmacokinetic effects of blood lipid changes, an existing CPF physiologically based pharmacokinetic/pharmacodynamic model for rats and humans was modified to account for altered lipid-tissue partition coefficients and for major physiological and biochemical changes of pregnancy. The model indicated that plasma CPF levels are expected to be proportional to the well-known changes in plasma lipids during gestation. There is a rapidly growing literature on the relationship of lipid profiles with different disease conditions and on birth outcomes. Increased blood concentrations of lipophilic chemicals like CPF may point to altered lipid status, as well as possibly higher levels of exposure. Thus, proper interpretation of blood biomonitoring data of lipophilic chemicals requires a careful consideration of blood lipids.

ABC transporter modulation: a strategy to enhance the activity of macrocyclic lactone anthelmintics

The emergence of parasites resistant to anthelmintic macrocyclic lactones (MLs) threatens to severely limit current parasite control strategies. Improving the current ML-based chemotherapy to perpetuate the efficacy of this broad-spectrum class of anthelmintics would be advantageous. In recent years it has become evident that the absorption, distribution and elimination of the MLs in hosts and parasites are under the control of multidrug resistance transporters (MDRs) such as P-glycoproteins. Theoretically, the inhibition of these transporters should result in an increase of the drug concentration in the organisms and higher treatment efficiency. This opinion article will discuss the recent findings in this research field and assess the possibilities of this approach being used in the field.