Trace analysis of endectocides in milk by high performance liquid chromatography with fluorescence detection.

An analytical method has been developed for the simultaneous determination of the following endectocide drugs in milk: ivermectin, abamectin, doramectin, moxidectin, eprinomectin, emamectin and nemadectin. Samples were extracted with acetonitrile, purified with solid-phase extraction on a reversed phase C(8), derivatised with N-methylimidazole, trifluoroacetic anhydride and acetic acid to a stable fluorescent derivative, and were further analysed by gradient high performance liquid chromatography (HPLC) on an endcapped reversed phase Supelcosil LC-8-DB. The derivatisation step was mathematically optimised and the method was validated according to the requirements of Commission Decision 2002/657/EC, using fortified raw bovine milk. Mean recovery was between 78 and 98%. The repeatability (CV(r)) and within-laboratory reproducibility (CV(W)) ranged from 4.6 to 13.4% and from 6.6 to 14.5%, respectively. Decision limits (CCalpha) for analytes with MRL values, namely eprinomectin and moxidectin, were determined to be 24.8 and 50.6 microg kg(-1), respectively. CCalpha values for unauthorised endectocides ranged from 0.1 to 0.2 microg kg(-1). Due to high acceptability regarding the required criteria and applicability to ovine and caprine milk, giving similar results, this multi-analyte method has been successfully implemented in pharmacokinetic research studies as well as statutory residue monitoring in Slovenia.

Linearity of eprinomectin pharmacokinetics in lactating dairy sheep following pour-on administration: excretion in milk and exposure of suckling lambs.

Pharmacokinetics of eprinomectin (EPR) were studied in blood plasma and milk in two groups of six Istrian Pramenka dairy sheep and their suckling lambs following pour-on administration of EPR to ewes at dose levels of 0.5 and 1mg/kg. Maximum concentration in plasma was 2.22 and 5.25 microg/l, and AUC was 13.6 and 33.7 microg day/l for the 0.5 and 1.0mg/kg dose, respectively. These results indicate that drug exposure with a dose of 0.5mg/kg, which is commonly used in cattle, may be subtherapeutic. The concentration time course in milk paralleled plasma concentrations. In the dose range studied, linear pharmacokinetics of EPR were demonstrated. Milk-to-plasma AUC ratio was 0.79+/-0.12 and 1.12+/-0.43; the fraction of dose recovered in milk was 0.037+/-0.011 and 0.058+/-0.027% for the low and high dose, respectively. Maximum residual levels in milk were below the maximum acceptable level of 20 microg/kg; however, EPR was detected in all samples investigated. Despite low permeability in milk, AUC in plasma of suckling lambs was between 20 and 30% of the AUC in plasma of ewes.

Analytical procedure for determination of the time profile of eprinomectin excretion in sheep faeces.

An analytical procedure has been introduced to enable study of the time profile of eprinomectin excretion in sheep faeces. Eprinomectin was extracted from sheep faeces with acetonitrile, the extract was cleaned by solid-phase extraction (SPE), and, after derivatization by reaction with N-methylimidazole, trifluoroacetic anhydride, and acetic acid, eprinomectin was analysed by high-performance liquid chromatography (HPLC) with fluorescence detection. The method has a low detection limit (1.0 ng g(-1) of moist sheep faeces), a low quantification limit (2.5 ng g(-1) of moist sheep faeces), good recovery (in the range 78.8 to 87.1%), and good reproducibility (RSD<10%). The method was used to study the time-profile of excretion of eprinomectin in sheep faeces after a single topical administration of 0.5 mg kg(-1) b.w. of the drug. Because of its good recovery, precision, and sensitivity, the method has also proved applicable to further ecotoxicological studies of eprinomectin.