Eprinomectin

Eprinomectin or [4’’-(epiacetylamino)-4’’-deoxyavermectin B₁] has recently been approved for use in the European Communauty as a beef and dairy topical endectocide under the tradename Eprinex pour-on for cattle. Eprinomectin is a new 16-membered macrocyclic lactone that belongs to the avermectin/milbemycin class of potent endectocides. It is a new endectocide consisting of a 90 + 10 mixture of two homologues: 4-epiacetyl-amino-4-deoxyavermectins B_1a and B_1b, which differ by one methylene unit at the C-25 portion of the macrocyclic ring (Fig 1). Eprinomectin was selected for development based on its potency and safety profile. One method for the detection of eprinomectin in bovine tissue has been reported, which involves solvent extraction and a solvent partioning clean-up step. Unfortunately, this method is time consuming and unusable for pharmacokinetic investigations.

In many instances, IVM is administered in conjunction with other related parasitic formulations to animals. Fig. 4 shows the GC separation of IVM from two other macrolide components, eprinomectin and moxidectin, which are often present with IVM in veterinary antiectoparasitic composite drug mixtures. As can be seen, the peaks due to moxidectin and eprinomectin had retention times of 11.7 and 24.2 min and were well resolved from those of IVM (14.0 min) and the Bp-d₁₀ internal standard (11.5 min). In addition, these two components could be quantitated using the same GC-MS method following TMS derivatization as described for IVM. Detection limits of 3.72 and 5.44 ng g^-1 were determined for eprinomectin and moxidectin, respectively (MS signals determined in the selective ion mode, Table 1). The linear dynamic ranges for these two components were ca. 0.28–71.4 μg g^-1 for eprinomectin and moxidectin, respectively.

The avermectins, a series of macrocyclic lactone endectocides, are the derivatives of natural fermentation products derived from the genus Streptomyces. The avermectin family mainly includes ivermectin, doramectin, moxidectin, emamectin, and eprinomectin (EPR). They are extremely effective against (endo-) internal and (ecto-) external parasites even in very low doses. Among the avermectin family, EPR was the first drug licensed for the treatment of parasitic infections in lactating cows because of its low residue level in cattle milk. Besides, EPR has a high activity for all the stages of the major gastrointestinal nematodes, lungworms, lice, horn flies and the mange mites of cattle, and has a significantly persistent activity for a range of major nematodes. However, the low water solubility (6.0–9.0 μg L^-1) of EPR reduces its bioavailability and persistence in oral or injection preparations. Therefore, the main dosage form of EPR is pour-on solutions. The repeated and indiscriminate application has resulted in treatment failures and resistance in some animal species. Worse still, with the pour-on solutions it is difficult to kill the endoparasites of livestock. These shortcomings of pour-on solutions restrict the application of EPR to a certain degree.