F. Imperiale

Ivermectin disposition kinetics after subcutaneous and intramuscular administration of an oil-based formulation to cattle

Slight differences in formulation may change the plasma kinetics and ecto-endoparasiticide activity of endectocide compounds. This work reports on the disposition kinetics and plasma availability of ivermectin (IVM) after subcutaneous (SC) and intramuscular (IM) administration as an oil-based formulation to cattle. Parasite-free Aberdeen Angus calves (n = 24; 240-280 kg) were divided into three groups (n = 8) and treated (200 microg/kg) with either an IVM oil-based pharmaceutical preparation (IVM-TEST formulation) (Bayer Argentina S.A.) given by subcutaneous (Group A) and intramuscular (Group B) injections or the IVM-CONTROL (non-aqueous formulation) (Ivomec, MSD Agvet) subcutaneously administered (Group C). Blood samples were taken over 35 days post-treatment and the recovered plasma was extracted and analyzed by HPLC using fluorescence detection. IVM was detected in plasma between 12 h and 35 days post-administration of IVM-TEST (SC and IM injections) and IVM-CONTROL formulations. Prolonged IVM absorption half-life (p < 0.05) and delayed peak plasma concentration (p < 0.001) were obtained following the SC administration of the IVM-TEST compared to the IVM-CONTROL formulation. No differences in total plasma availability were observed among treatments. However, the plasma residence time and elimination half-life of IVM were significantly longer after injection of the IVM-TEST formulation. IVM plasma concentrations were above 0.5 ng/ml for 20.6 (CONTROL) and 27.5 days (IVM-TEST SC), respectively (p < 0.05). The modified kinetic behaviour of IVM obtained after the administration of the novel oil-based formulation examined in this trial, compared to the standard preparation, may positively impact on its strategic use in cattle.

Uptake of albendazole and albendazole sulphoxide by Haemonchus contortus and Fasciola hepatica in sheep.

The pattern of in vivo uptake of albendazole (ABZ) and its major metabolite, ABZ-sulphoxide (ABZSO), by Haemonchus contortus and Fasciola hepatica recovered from ABZ-treated sheep, was investigated. Concentration profiles of both compounds were simultaneously measured in target tissues/fluids from the same infected sheep. In addition, the proportion of the (+) and (-) ABZSO enantiomers was determined in plasma, bile and F. hepatica recovered from treated sheep. Sheep naturally infected with H. contortus were intraruminally (i.r.) treated with ABZ (micronized suspension, 7. 5mg/kg) and the plasma concentrations of ABZSO and ABZ-sulphone (ABZSO(2)) determined in addition to the concentration of ABZ and ABZSO in H. contortus, abomasal mucosa and fluid content samples. In addition, F. hepatica artificially infected sheep were treated i.r. with the same ABZ suspension (7.5mg/kg), and samples of blood, bile, liver tissue and adult flukes were collected and analysed by HPLC to determine the concentrations of ABZ and both enantiomers of ABZSO. ABZSO and ABZSO(2) were the analytes recovered in plasma with ABZ and ABZSO present in H. contortus. ABZ was the analyte recovered at the highest concentration in H. contortus and abomasal mucosa, whereas higher concentrations of ABZSO were measured in abomasal fluid content. Only low concentrations of ABZ were detected in F. hepatica and bile, but markedly higher concentrations of ABZ were measured in liver tissue. ABZSO was the main molecule recovered in F. hepatica, plasma and bile samples collected from ABZ-treated sheep. The (+) enantiomer of ABZSO was recovered at a higher proportion in plasma (75%), bile (78%) and F. hepatica (74%) after ABZ administration to infected sheep.

Thermal stability of antiparasitic macrocyclic lactones milk residues during industrial processing

The chemical stability of residues of different antiparasitic macrocyclic lactone compounds in milk subjected to thermal treatment was assessed. Concentrations of ivermectin (IVM), moxidectin (MXD) and eprinomectin (EPM) in sheep milk, equivalent to those measured in vivo in milk excretion studies, were subjected to 65°C over 30 min or to 75°C for 15 s. Residue concentrations of IVM, MXD and EPM in milk were measured by high-performance liquid chromatography (HPLC) (fluorescence detection) before and after heat treatment of the drug-fortified milk samples. No evidence of chemical loss was obtained in either of the thermal treatments under evaluation. The stability of the parent compounds in milk was evidenced by the lack of bioconversion products (metabolites) after both thermal treatments. Only very minor changes on drug concentrations were observed at the end of the treatments, which fell within the limits of the variation of the validated analytical method. In conclusion, residue concentrations of macrocyclic lactones are unaffected by industrial-simulated milk thermal procedures. Based on the reported findings, it can be postulated that residue concentrations of IVM, MXD and EPM measured in raw sheep milk may be used to estimate consumer exposure and dietary intake for these veterinary drugs.

Residual concentrations of the flukicidal compound triclabendazole in dairy cows’ milk and cheese

Triclabendazole (TCBZ) is a flukicidal halogenated benzimidazole compound extensively used in veterinary medicine. Liver fluke control in lactating dairy cattle is difficult because treatment should be implemented only during the dry period to avoid milk residues. However, control in endemic areas is usually implemented as regular treatments three to four times a year, even during the lactating period. Thus, information on TCBZ milk excretion and the risk of the presence of drug residues in fluid milk and milk-derivate products is essential. The experimental aims were to evaluate the comparative disposition kinetics of TCBZ and its sulpho-metabolites in plasma and milk in lactating dairy cattle after the oral administration (12 mg kg−1) of TCBZ and to assess the pattern of residues in cheese made with milk from treated dairy cows. Both TCBZ sulphoxide and sulphone metabolites but not TCBZ were detected in milk (up to 36 and 144 h, respectively) and plasma (up to 144 h) after oral administration of TCBZ. Residual concentrations of TCBZ sulpho-metabolites were found in cheese made with milk from treated animals. The total average residual concentration in fresh cheese was 13.0-fold higher than that obtained in milk used for its elaboration. The high concentrations of TCBZ sulpho-metabolites recovered in fresh cheese should be seriously considered before milk from treated cows is used for making dairy products.

Licking induced changes to the pattern of moxidectin milk elimination after topical treatment in dairy cows.

Pour-on administration of the macrocyclic lactones anti-parasitic compounds in beef and dairy cattle is now worldwide accepted. However, the information available on their milk excretion pattern, after topical administration is rather limited. Additionally, the cattle licking behaviour has been proven to affect the kinetics of these anti-parasitic compounds. The purpose of this study was to investigate the influence of the natural licking behaviour on the plasma and milk disposition of moxidectin (MXD), topically administered (500 microg/kg) in lactating dairy cows. Ten lactating Holstein dairy cows (705 kg body weight) were allocated into two experimental groups (n = 5). The licking was prevented during 5 days postadministration in animals in group I, and the remaining cows (group II) were allowed to lick freely. MXD concentrations profiles were measured in plasma and milk over 15 days posttreatment. The licking restriction period caused marked changes in MXD disposition kinetics both in plasma and milk. Both plasma and milk MXD concentrations (partial AUC 0-5 days) were significantly lower (P < 0.05) in licking-restricted cows. After the 5-day of restriction period, the animals were allowed to lick freely, which permitted the oral ingestion of MXD, situation clearly reflected both in plasma profile and milk excretion pattern. Despite the enhanced MXD milk concentrations measured in free-licking cows, drug concentrations did not reach the maximum MXD residues limit.

Failure of ivermectin and eprinomectin to control Amblyomma parvum in goats: Characterization of acaricidal activity and drug pharmacokinetic disposition

The therapeutic efficacies of ivermectin (subcutaneous injection) and eprinomectin (topical treatment) given at two different dosage levels to goats naturally infested with Amblyomma parvum were assessed. Treatments included subcutaneous injection of ivermectin at 0.2 and 0.4mg/kg and extra-label pour-on administration of eprinomectin at 0.5 and 1mg/kgb.w. Ivermectin and eprinomectin failed to control Amblyomma parvum on goats. Treatment with ivermectin resulted in a low number of engorged female ticks in relation to untreated control goats and, at the highest dose rate (0.4mg/kg), the female engorgement weights were significantly lower and the pre-oviposition period significantly longer than those observed in ticks recovered from untreated control goats. The tick efficacy assessment was complemented in a separate group of tick-free goats with a pharmacokinetic characterization of eprinomectin (topically administered at 0.5, 1.0 and 1.5mg/kg) and ivermectin (subcutaneous treatment given at (0.2 and 0.4mg/kg) in goats. Heparinized blood samples were taken between 0 and 21 days post-treatment. Higher and more persistent drug plasma concentrations were recovered after the subcutaneous treatment with ivermectin compared to those obtained for eprinomectin topically administered. The understanding of the relationship among the pattern of drug absorption, the kinetic disposition and the resultant clinical efficacy is relevant to improve the poor performance observed for ivermectin and eprinomectin against A. parvum on goats.

Determination of ivermectin and moxidecin residues in bovine milk and examination of the effects of these residues on acid fermentation of milk

Ivermectin (IVM) and moxidectin (MXD) are broad-spectrum antiparasitic drugs not approved for use in dairy animals, although their use in dairy sheep, goats and cattle nevertheless occurs in many parts of the world. The work reported here describes (1) the application of an HPLC method (including milk samples clean-up and chemical extraction) to quantify IVM and MXD residues in bovine milk, and (2) an assessment of the effect of different IVM and MXD concentrations on bovine milk acid fermentation. The latter was carried out using the ‘yoghurt test’ to determine the minimum IVM and MXD concentrations affecting milk acid fermentation. The sample clean-up, chemical extraction and the validated HPLC method allowed the quantification of IVM and MXD up to 0.1 ng ml-1 in milk with acceptable validation coefficients. Drug recoveries from fortified milk samples ranged between 72% (CV = 9.1%) and 75% (CV = 13.3%) for MXD and IVM, respectively. Neither IVM nor MXD affected the acid fermentation of bovine milk. In fact, there was no drug-induced changes on milk acidity even at IVM and MXD concentrations as high as 1000 ng ml-1. These results indicate that the yoghurt biological test is not suitable to evaluate the presence of milk residues for these antiparasitic compounds. Thus, a highly sensitive HPLC technique is the only reliable method for determining the presence of residual concentrations of IVM and MXD in milk and dairy products to assure consumer safety.

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

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

Eprinomectin accumulation in Rhipicephalus (Boophilus) microplus: Pharmacokinetic and efficacy assessment.

Eprinomectin (EPM) is a macrocyclic lactone used against endo-ectoparasites without withdrawal time in milk and meat after its pour-on administration at 0.5mg/kg. Previous experiments evaluated the efficacy of EPM against Rhipicephalus (Boophilus) microplus in cattle. This study assessed EPM efficacy against R. (B.) microplus after topical administration at two dose rates and investigated the relationship between EPM systemic exposure in the host and drug concentrations accumulated in ticks recovered from treated animals. A standardized pharmaco-parasitological study was performed in two phases. In phase 1 eighteen Braford cattle naturally infected with R. (B.) microplus were divided into three experimental groups with a similar level of infestation (Kruskal-Wallis test, P>0.05): control group and treated groups with EPM pour-on (1 and 1.5mg/kg). Samples of heparinized blood and ticks at different life stages were taken between 0 and 21 days (d) post-administration to measure EPM concentrations by HPLC. The efficacy trial (phase 2) included eighteen Braford calves naturally infected with R. (B.) microplus divided into control group and 1mg/kg and 1.5mg/kg EPM treated groups. Female ticks (4.5-8mm) on cattle were counted between 1 and 23 days post-treatment to evaluate the efficacy of EPM. The reproductive efficiency index (REI) and the fertility efficiency index (FEI) were evaluated. Plasma concentrations of EPM showed a linear relationship with the level of dose rate administered. Peak plasma concentrations were within a range between 13.8 and 90ng/ml, which guarantee milk drug concentrations below the maximum residues level. High EPM concentrations were detected in ticks. EPM concentrations in R. (B.) microplus were correlated to plasma concentrations between 1.25 days and 21 days post-administration (r 0.84; P<0.05). EPM efficacy calculated using the Henderson-Tilton formula was 98.9% and 99.1% (7 days post-administration) and 100% (23 days post-administration) after EPM treatment at 1 and 1.5mg/kg, respectively. EPM administered at 1.5mg/kg also showed a significantly higher deleterious effect on tick fertility as measured by FEI (P<0.01). Therefore, treatment with EPM may be useful for controlling ticks in cattle, particularly in dairy production systems.