A method was developed and validated to determine eprinomectin marker residue in bovine liver, kidney, muscle, and fat. The overall percent recovery (( CV) was 93 ( 12% (n ) 66) for liver, 100( 13% (n ) 34) for muscle, 87 ( 13% (n ) 42) for kidney, and 95 ( 11% (n ) 42) for fat. The limit of detection was 1 ng/g, the lower limit of quantitation was 2 ng/g, and the upper limit of quantitation was 5000 ng/g (µg/kg). Accuracy, precision, linearity, selectivity, and ruggedness were demonstrated. For the determination, tissue is mixed with sodium sulfate, homogenized, and extracted. The reconstituted extract is loaded onto an aminopropyl cartridge. After solvent exchange, a portion of the eluate is derivatized precolumn via automated addition of TFAA in acetonitrile and analyzed using fluorescence detection. The method is rapid, sensitive, and selective and provides for determination of eprinomectin marker residue in edible bovine tissue from the low parts per billion (ng/g) level to the parts per million level. The method has been successfully performed by several different analysts.
An analytical method has been developed for the extraction, derivatization, and fluorescence HPLC determination of MK-0244 [4"-deoxy-4"-(epimethylamino)avermectin B1 benzoate salt] and its delta 8,g-isomer from lettuce and celery at trace (parts per billion) levels. MK-0244 and its delta 8,g-isomer are extracted with methanol, and the extract is cleaned up on a reverse-phase CS cartridge followed by a liquid-liquid extraction with ethyl acetate before passing through a propyl sulfonyl cation-exchange cartridge. MK-0244 and its delta 8,g-isomer are then derivatized with trifluoroacetic anhydride/ 1-methylimidazole/acetonitrile reagent system to form a fluorescent derivative which is separated on a reverse-phase HPLC system and detected with a fluorescence detector. The average recoveries were 95 f 10% for celery and 96 f 8% for lettuce. For both lettuce and celery matrix, concentrations as low as 2 ppb (SIN = 10) can be detected in a 10-g sample. This method was used to determine the MK-0244 levels in samples from a lettuce field trial.
A series of 10 dose confirmation studies was conducted to evaluate the persistent activity of an extended-release injectable (ERI) formulation of eprinomectin against single point challenge infections of gastrointestinal and pulmonary nematodes of cattle. The formulation, selected based on the optimal combination of high nematode efficacy, appropriate plasma profile, and satisfactory tissue residue levels, includes 5% poly(D,L-lactide-co-glycolic)acid (PLGA) and is designed to deliver eprinomectin at a dose of 1.0mg/kg bodyweight. Individual studies, included 16-30 cattle blocked based on pre-treatment bodyweight and randomly allocated to treatment with either ERI vehicle or saline (control), or the selected Eprinomectin ERI formulation. Treatments were administered once at a dose volume of 1 mL/50 kg bodyweight by subcutaneous injection in front of the shoulder. In each study, cattle were challenged with a combination of infective stages of gastrointestinal and/or pulmonary nematodes 100, 120 or 150 days after treatment and were processed for parasite recovery according to standard techniques 25-30 days after challenge. Based on parasite counts, Eprinomectin ERI (1mg eprinomectin/kg bodyweight) provided >90% efficacy (p<0.05) against challenge with Cooperia oncophora and Cooperia surnabada at 100 days after treatment; against challenge with Ostertagia ostertagi, Ostertagia lyrata, Ostertagia leptospicularis, Ostertagia circumcincta, Ostertagia trifurcata, Trichostrongylus axei, and Cooperia punctata at 120 days after treatment; and against challenge with Haemonchus contortus, Bunostomum phlebotomum, Oesophagostomum radiatum and Dictyocaulus viviparus at 150 days after treatment. Results of a study to evaluate eprinomectin plasma levels in cattle treated with the Eprinomectin ERI formulation reveal a characteristic second plasma concentration peak and a profile commensurate with the duration of efficacy. These results confirm that the Eprinomectin ERI formulation can provide high levels of parasite control against a range of nematodes of cattle for up to 5 months following a single treatment.
Pharmacokinetics and anthelmintic activity of topical eprinomectin in goats prevented from physical contact to others and self-grooming were studied. Sixteen approximately 7 months old male castrated German White Noble goats harbouring induced infections of gastrointestinal nematode parasites were included in the study. They were blocked based on pre-treatment body weight (range 22.4 to 36.4 kg) and then randomly allocated to the untreated control group or the group treated with topical 0.5% w/v eprinomectin (EPRINEX Pour-on, Merial) at 1 mg/kg body weight. Plasma samples were collected prior to and at intervals up to 14 days following treatment and analyzed to determine the concentrations of eprinomectin (B1a component). Parasites were recovered, identified, and counted following necropsy 14 days after treatment. Goats treated with topical eprinomectin had significantly fewer (≥99% reduction, p < 0.01) adult Cooperia curticei, Haemonchus contortus, Nematodirus battus, Oesophagostomum venulosum, Ostertagia circumcincta, and Trichostrongylus colubriformis than the untreated controls. Basic pharmacokinetic parameters for eprinomectin B1a were AUCinfinity, 37.1 ± 15.2 day ng/mL; T½, 5.11 ± 2.83 days; and Cmax, 5.93 ± 1.87 ng/mL; individual maximal concentrations were observed 1 or 2 days after treatment. Results of this study indicate that oral ingestion is not required to achieve adequate exposure for excellent anthelmintic efficacy following topical administration of eprinomectin at 1 mg/kg body weight to goats.
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