Since there is no registered anthelmintic drug available for use in goats, extra-label use of drugs is a common practice in most countries. The aim of the present study was to compare the pharmacokinetic disposition of levamisole (LVM)-oxyclozanide (OXZ) combination in sheep and goats following per os administration. Goats (n = 8) and sheep (n = 8) 12- to 16-months-old were used for this study. The animals received tablet formulation of LVM and OXZ combination orally at a dose of 7.5 mg/kg and 15 mg/kg body weight, respectively. Blood samples were collected by jugular vein at different times between 5 min and 120 h after drug administrations. The plasma concentrations of LVM and OXZ were analyzed by HPLC following liquid-liquid phase extraction procedures. The plasma concentrations and systemic availabilities of both LVM and OXZ in goats were lower and the plasma persistence of LVM was shorter compared with those observed in sheep. Terminal half-lives (t1/2λz) of both molecules are shorter in goats compared with those in sheep. Goats treated with LVM-OXZ combination at the recommended dose for sheep may result in a reduced efficacy, because of under-dosing, which may increase the risk of drug resistance in parasites. Increased or repeated dose could be a strategy to provide higher plasma concentration and thus to improve the efficacy against the target parasites in goats compared with sheep. However, some adverse reactions may occur since LVM has relatively very narrow therapeutic index due to its nicotine-like structure and effect.
Levamisole (LVM), the laevo-rotary isomer of tetramisole [2,3,5,6-tetrahydro 6–phenyl imidazo (2,1-b) thiazole] is a broad-spectrum anthelmintic drug active against most nematodes (1) and widely used in veterinary medicine. Levamisole induces spastic paralysis in the target nematodes as a result of permanent muscle contraction. Oxyclozanide (OXZ) [2,3,5-trichloro-N-(3,5- dichloro-2-hydroxyphenyl)-6-hydroxybenzamide] is a salicylanilide anthelmintic drug that mainly acts by uncoupling oxidative phosphorylation in flukes (2,3). It is used for the treatment and control of adult stages of liver flukes in large and small ruminant species (4,5). Combination of anthelmintics formulated has been used to provide positive results against resistant nematodes (6–8) and broad-spectrum control of different types of internal parasites, e.g., nematodes and tapeworms or nematodes and liver flukes in ruminants.
The extra-label use of drugs is a common practice in goats. The high prevalence of anthelmintic-resistant nematodes in goats is probably due to the extensive extra-label use of drug at the sheep doses recommended, corresponding to a drug under-dosage. It has been reported that the metabolism of many therapeutic drugs, including anthelmintics, differs between sheep and goats (9–17). The drug molecules are more rapidly metabolized and eliminated from blood in goats compared with sheep. Hence, administration of anthelmintic drugs to goats at an ovine dosage has resulted in a reduced efficacy, because of under-dosing. This may explain the differences in the prevalence of anthelmintic resistance in nematode populations in goats compared with sheep in particular for multi-resistant strains (14,18). Therefore, the purposes of this study were to compare the pharmacokinetic disposition of LVM-OXZ combination in sheep and goats and to find out whether the dose recommended for sheep can be applied in goats following per os administration.
Materials and methods
Eight goats [mean body weight (BW): 23.1 ± 4.2 kg] and 8 sheep (mean BW: 24.8 ± 2.9 kg) that were 12- to 16-months old were used in this investigation. They were housed and fed with wheat straw, fodder, and concentrate feed. Water was supplied ad libitum. This study was approved by Animal Ethic Committee of University of Adnan Menderes.
Treatment and sampling
The animals received tablet formulation of LVM and OXZ combination (Zelensin, 375 mg LVM HCl + 750 mg OXZ, Sanovel, Istanbul, Turkey) orally at a dose of 7.5 mg/kg BW and 15 mg/kg BW, respectively. Heparinized blood samples (5 mL) were collected by jugular venipuncture prior to drug administration then at 5, 10, 15, and 30 min, 1, 1.5, 2, 4, 8, 12, 16, 24, 32, 48 h and 3, 4, 5, 6, and 8 days.
The plasma concentrations of LVM and OXZ were analyzed by high-performance liquid chromatography (HPLC) following liquid-liquid phase extraction. Stock solutions (100 μg/mL) of pure standard of LVM hydrochloride and OXZ (Sigma, St. Louis, Missouri, USA) were prepared using acetonitrile and water (50:50) as the solvent. These were diluted to give 0.01, 0.05, 0.1, 0.5, 1, 5, 10, and 20 μg/mL standard solutions for plasma for calibration as standard curves and to add to drug-free plasma samples to determine the recovery of both molecules.
Extraction from plasma
Plasma concentrations of LVM and OXZ were determined by HPLC with ultraviolet detection according to methods previously described by Garcia et al (19) and Jo et al (20) with some modifications, respectively.
For LVM analysis, drug-free plasma samples (1 mL) were spiked with standard of LVM to reach the following final concentrations: 0.025, 0.05, 0.1, 0.5, 1 and 5 μg/mL. Water (1 mL) and 0.5 mL of 10 N sodium hydroxide were added to 10 mL-ground glass tubes containing 1 mL spiked or experimental plasma samples. After mixing by vortex for 15 seconds, 6 mL ethyl ether:nhexane (80:20, vol/vol), was added. The sample tubes were stoppered and shaken for 10 min on a rotary mixer. After centrifugation at 3000 × g for 10 min, the upper organic phase was transferred to a thin-walled 10 mL-conical glass tube and evaporated to dryness at 40°C in a rota vapor (Maxi-Dry plus, Heto, Denmark). The dry residue was reconstituted with 250 μL mobile phase. Then, the tubes were placed in an ultrasonic bath and finally, 50 μL of this solution was injected into the chromatographic system.
For OXZ analysis, drug-free plasma samples (1 mL) were spiked with standard of OXZ to reach the following final concentrations: 0.05, 0.1, 0.5, 5, 10, and 20 μg/mL. Acetonitrile (2 mL) was added, and the sample was mixed by vortex (10 s). Anhydrous sodium sulphate (1 g) was added, and the sample tubes were stoppered and shaken for 10 min on a rotary mixer. The samples were centrifuged at 3000 × g for 10 min thereafter, and extracted once again with 2 mL of acetonitrile. The organic layers were recovered after 20 min of centrifugation at 3000 × g. Then n-hexane (5 mL) was added to the combined supernatant. After shaking, the upper phase was discarded after 10 min of centrifugation at 3000 × g. The lower phase was transferred to a thin-walled 10 mL-conical glass tube and evaporated to dryness at 40°C in a rota vapor (Maxi-Dry plus). The dry residue was reconstituted with 250 μL mobile phase. Then, the tubes were placed in an ultrasonic bath and finally, 50 μL of this solution was injected into the chromatographic system.
High-performance liquid chromatography system
The mobile phase consisted of acetonitrile and water (2% acetic acid) (20:70, v/v) and was delivered (1100 Series, QuatPump Agilent, Waldron, Germany) at an isocratic flow rate of 1 mL/min. A nucleosil C18 analytical column (Luna, 4 μm, 150 mm × 4.6 mm; Phenomenex, Macclesfield, Cheshire, UK) with nucleosil C18 guard column was used for analysis of the molecules. Ultraviolet detection (1100 Series, Agilent, Waldron, Germany) was at a wavelength of 225 nm for LVM analysis.
Oxyclozanide were determined using same HPLC system and eluted with a mobile phase consisting of a mixture of acetonitrile and 0.1% phosphoric acid (40:60, v/v). The isocratic mode was run at a flow rate of 1 mL/min and an ultraviolet detector was operated at 300 nm.
The analytical methods used for LVM and OXZ in plasma samples were validated before analysis of the experimental samples. The analytes were identified with the retention time of pure reference standards. Recoveries of the molecules under study were measured by comparison of the peak areas from spiked plasma samples with the areas resulting from direct injections of standard solutions. The inter- and intra-assay precisions of the extraction and chromatography procedures were evaluated by processing replicate aliquots of previously drug-free goat and sheep plasma samples containing known amounts of the drugs on different days.
The calibration graphs for LVM and OXZ were prepared (linear range 0.025 to 10 μg/mL). The slopes of the lines between peak areas and drug concentrations were determined by least squares linear regression and correlation coefficient (r) and coefficient of variations (CV) calculated. Linearity was established to determine the drug concentration/detector response relationship. The detection limits of the both LVM and OXZ were established with HPLC analysis of blank plasma fortified with the standard, measuring the baseline noise at the retention time of the peak. The mean baseline noise at the peak retention time plus 3 standard deviations was defined as the detection limit (LOD). The mean baseline noise plus 6 standard deviations was defined as the limit of quantification (LOQ).
Pharmacokinetic and statistical analysis of data
The plasma concentration versus time curves obtained after each treatment in individual animals, were fitted with the WinNonlin software program (Version 5.2; Pharsight Corporation, Mountain View, California, USA). Pharmacokinetic parameters for each animal were analyzed using non-compartmental model analysis with extravascular input for LVM and OXZ. The maximum plasma concentration (Cmax) and time to reach maximum concentration (tmax) were obtained from the plotted concentration-time curve of each drug in each animal. The trapezoidal rule was used to calculate the area under the plasma concentration time curve (AUC). The mean residence time (MRT) was calculated as:
MRTlast = AUMClast/AUClast
Terminal half-life (t1/2λz) was calculated as:
t1/2λz = - ln(2)/λz
Where: λz represents the first-order rate constant associated with the terminal (log linear) portion of the curve.
The pharmacokinetic parameters obtained from each animal were reported as a median with interquartile ranges (Q1–Q3) and statistically compared by the Mann-Whitney U-test between sheep and goats. The values were considered significantly different at P < 0.05.
The analytic procedures and HPLC analysis of LVM and OXZ were validated before analysis of experimental samples. Mean recoveries of LVM and OXZ from plasma were 86.31% and 74.12% with a relative SD < 10%, respectively. The limit of detections and limit of quantification for LVM and OXZ were 0.014 to 0.043 μg/mL and 0.011 to 0.032, respectively. The inter-assay and intra-assay precisions of the extraction and chromatography procedures were evaluated by processing on different days 6 replicate aliquots of drug-free sheep or goat plasma samples that contained known amounts of LVM and OXZ. The precision determined at each concentration was < 15% of the coefficient of variation, and accuracy ranged from 92% to 106% for both molecules.
Median (with Q1–Q3 ranges) pharmacokinetic parameters of LVM and OXZ combination in goats and sheep are shown in Table I with the plasma concentration versus time curves (Figures 1 and and2,2, respectively). This study indicated that the plasma dispositions of both LVM and OXZ in goats were significantly different to those observed in sheep following oral administration at same dose rates. Although no significant difference was found for maximum plasma concentration (Cmax: 1.63 μg/mL versus 1.07 μg/mL), significantly larger area under the concentration vs. time curve (AUC: 8.75 μg.h/mL versus 2.09 μg.h/mL), longer terminal half-life (t1/2λz: 7.91 h versus 3.81 h) and mean residence time (MRT: 7.11 h versus 2.69 h) were observed in sheep as compared with those observed in goats for LVM, respectively. In addition, Cmax (11.01 μg/mL versus 6.68 μg/mL), AUC (488.70 μg.h/mL versus 309.33 μg.h/mL) and t1/2λz (21.74 h versus 18.71 h) values of OXZ in sheep were significantly higher and longer compared with those values observed in goats, respectively.
Plasma disposition versus time curves of levamisole (LVM) in goats and sheep following single per os administration (n = 8).
Plasma disposition versus time curves of oxyclozanide (OXZ) in goats and sheep following single per os administration (n = 8).
Median pharmacokinetic parameters with the interquartile (IQ) ranges (Q1–Q3) of levamisole (LVM) and oxyclozanide (OXZ) combination in sheep and goats following single per os administration (n = 8)
The plasma concentrations of both LVM and OXZ in sheep were considerably higher and the plasma persistence of LVM was longer compared with those observed in goats following oral administration. The origin of the lower plasma concentration of both molecules in goats is unclear. The most likely explanation is that goats have greater metabolic capacity and elimination capability of anthelmintic compounds than do sheep, as has been previously demonstrated with LVM (21) and other broad-spectrum anthelmintic groups such as benzimidazoles (10) and macrocyclic lactones (22–24). Moreover, it was reported that goats were better adapted to tolerate and detoxify plant toxins compared with sheep (25,26).
Levamisole rapidly reached the plasma peak concentrations at 0.08 h in sheep and goats after oral administration. These values are similar to those obtained by Galtier et al (21) in sheep (0.083 h) and goats (0.166 h). On the other hand, Cmax (1.63 μg/mL and 1.07 μg/mL) and t1/2 (7.94 h and 3.67 h) values of LVM observed in the present study are higher and longer than those reported by Galtier et al (21) in sheep (Cmax: 1.06 μg/mL and t1/2: 1.2 h) and goats (Cmax: 0.63 μg/mL and t1/2: 1.25 h), respectively. In addition, Fernandez et al (27) and Sahagún et al (28) obtained much lower plasma concentration for LVM in sheep compared with the present study following per os administration at same rates. The origin of the differences between studies is unclear. These differences may in part be due to differences in methodology or experimental conditions since different feeding regime, formulation, and parasitological status could have caused differences in absorption, disposition, and persistence of anthelmintic drugs in the animals. In this study, tablet formulation of LVM/OXZ combination was administered to animals, whereas Galtier et al (21), and Fernandez et al (27), and Sahagún et al (28) administered LVM as an oral drench and solution, respectively. Moreover, there was the possibility of a drug-drug interaction, due to co-administration of both drugs. However, there is no information available in the literature on this kind of interaction for LVM and OXZ.
The present study indicates that the plasma concentration of OXZ in sheep is significantly greater than that in goats. The Cmax (13.24 μg/mL) and AUC (621.46 μg.h/mL) values of OXZ in sheep more than 2 times higher and larger than those observed in goats (6.83 μg/mL and 294.70 μg.h/mL) after per os administration, respectively. Moreover, terminal half-life of OXZ in goats is significantly shorter than that observed in sheep. Similar differences of OXZ as observed with LVM disposition between 2 species supports that goats have lower systemic availability and faster elimination process compared with sheep. As closantel and rafoxanide are the most widely used salicylanilide group anthelmintics, they are more extensively studied in different animal species [reviewed by Swan (29)]. Nevertheless, there is a paucity of data available in the literatures on the pharmacokinetics of OXZ in animals and this is reported first herein. A radiolabel study of 14C-oxyclozanide was conducted in sheep following a single dose rate of 15 mg/kg BW formulated as a commercial drench (30). The highest plasma radioactivity of 10 to 20 μg/mL (Cmax) was found at 8 h (tmax) after administration. Moreover, the plasma dispositions of rafoxanide, closantel, and OXZ in sheep following per os administration described by Mohammed- Ali and Bogan (31). The findings of OXZ from the present study in sheep are not similar to those obtain by Mohammed-Ali and Bogan (31). Cmax (19.0 μg/mL), AUC (1224 μg.h/mL), and t1/2 (153.6 h) values of OXZ were much greater and longer compared with those observed in this study, respectively. These differences are probably related to the methodology of the previous study, since the number of sampling times seems insufficient to determine the actual parameters such as Cmax and t1/2 values.
In conclusion, the plasma concentrations of both LVM and OXZ in goats were significantly lower and the plasma persistence of LVM was significantly shorter compared with those observed in sheep following per os co-administration. Goats treated with LVM-OXZ combination at the recommended dose for sheep may result in a reduced efficacy, because of under-dosing, which may increase the risk of drug resistance in internal parasites. Increased or repeated dose could be a strategy to provide higher and more persistent plasma concentration and thus improve the efficacy against the target parasites in goats compared with sheep. However, some adverse reactions may occur since LVM has a relatively narrow therapeutic index due to its nicotine-like structure and effect.
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Post time: Nov-15-2021