A sensitive method for the measurement of the novel pet endectocide, selamectin (UK-124,114), in dog and cat plasma by chemical derivatisation and high-performance liquid chromatography with fluorescence detection

Distribution of emamectin benzoate in Atlantic salmon (Salmo salar L.)

The aims of this study were to investigate the content of emamectin in blood, mucus and muscle following field administration of the recommended dose, and correlation with sea lice infection on the same fish (elimination study). The tissue distribution of tritiated emamectin benzoate after a single oral dose in Atlantic salmon was also investigated by means of whole-body autoradiography and scintillation counting (distribution study). In the elimination study, concentrations of emamectin benzoate reached maximum levels of 128, 105 and 68 ng/g (p.p.b.) for blood, mucus and muscle respectively, on day 7, the last day of administration. From day 7, the concentration in the blood declined until concentration was less than the limit of detection on day 77. The concentration was higher in mucus compared with plasma (P < 0.05) except on days 7 and 21. The concentration of emamectin benzoate decreased gradually from the end of treatment (day 7) to day 70 with half-lives of 9.2, 10.0 and 11.3 days in muscle, plasma and mucus respectively. The distribution study demonstrated a high quantity of radioactivity in mucous membranes (gastrointestinal tract, gills) throughout the observation period (56 days). Activity was high in the epiphysis, hypophysis and olfactory rosette throughout the study. The highest activity was observed in the bile, indicating this to be an important route for excretion. The distribution study confirmed the results from the elimination study with respect to concentrations in blood, skin mucous and muscle.

Use of near-infrared spectrometry for quantitative determinations of selamectin and moisture in topical formulations

A rapid near-infrared spectrometric (NIR) method was qualified for use with the quantitative analysis of selamectin and moisture in topical formulations. Selamectin is currently marketed as a pet endectocide and is available in several formulations for cats and dogs. The use of NIR in this investigation replaces the in-process testing by liquid chromatography and concurrently provided moisture content that would otherwise only be available with additional Karl Fischer titration investigations. A seven-factor partial least square regression (PLS) of the second derivative spectra encompassing the wavelength region of 1450-2200 nm was used to quantify both selamectin and moisture content. A second three-factor PLS solely for water content was also applied and compared with the full model. This qualification confirms that this method may be used to quantitate selamectin and moisture as a process tool or to examine finished good samples. Each sample can be rapidly analyzed within 5 min on the current bench top system.

Pharmacokinetics of selamectin following intravenous, oral and topical administration in cats and dogs

The pharmacokinetics of selamectin were evaluated in cats and dogs, following intravenous (0.05, 0.1 and 0.2 mg/kg), topical (24 mg/kg) and oral (24 mg/kg) administration. Following selamectin administration, serial blood samples were collected and plasma concentrations were determined by high performance liquid chromatography (HPLC). After intravenous administration of selamectin to cats and dogs, the mean maximum plasma concentrations and area under the concentration-time curve (AUC) were linearly related to the dose, and mean systemic clearance (Clb) and steady-state volume of distribution (Vd(ss)) were independent of dose. Plasma concentrations after intravenous administration declined polyexponentially in cats and biphasically in dogs, with mean terminal phase half-lives (t(1/2)) of approximately 69 h in cats and 14 h in dogs. In cats, overall Clb was 0.470 +/- 0.039 mL/min/kg (+/-SD) and overall Vd(ss) was 2.19 +/- 0.05 L/kg, compared with values of 1.18 +/- 0.31 mL/min/kg and 1.24 +/- 0.26 L/kg, respectively, in dogs. After topical administration, the mean C(max) in cats was 5513 +/- 2173 ng/mL reached at a time (T(max)) of 15 +/- 12 h postadministration; in dogs, C(max) was 86.5 +/- 34.0 ng/mL at T(max) of 72 +/- 48 h. Bioavailability was 74% in cats and 4.4% in dogs. Following oral administration to cats, mean C(max) was 11,929 +/- 5922 ng/mL at T(max) of 7 +/- 6 h and bioavailability was 109%. In dogs, mean C(max) was 7630 +/- 3140 ng/mL at T(max) of 8 +/- 5 h and bioavailability was 62%. There were no selamectin-related adverse effects and no sex differences in pharmacokinetic parameters. Linearity was established in cats and dogs for plasma concentrations up to 874 and 636 ng/mL, respectively. Pharmacokinetic evaluations for selamectin following intravenous administration indicated a slower elimination from the central compartment in cats than in dogs. This was reflected in slower clearance and longer t(1/2) in cats, probably as a result of species-related differences in metabolism and excretion. Inter-species differences in pharmacokinetic profiles were also observed following topical administration where differences in transdermal flux rates may have contributed to the overall differences in systemic bioavailability.

Isolation and multiresidue detection of macrolide endectocides present in animal matrices

A simple, rapid, and sensitive method for isolation and detection of macrolide endectocides (moxidectin, doramectin, selamectin, ivermectin, and eprinomectin) in animal sera and liver is described. Fortified sera or homogenized liver samples were treated with sodium chloride followed by organic solvent extraction. No additional steps were required prior to analysis. Separation of analytes and collection of mass information was achieved by liquid chromatography/mass spectrometry with positive atmospheric pressure chemical ionization set in selected ion monitoring mode with each sample analysis complete in 15 minutes. Presence of each compound was confirmed based on 2 separate extracted ion profiles. Detection of avermectins and moxidectin in a range of working standards was achieved at 10, 50, and 100 ppb. Quantitation of these compounds in fortified samples was based on standard calibration curves with R2 > 0.99. Detection limits of 10 ppb for ivermectin, moxidectin, and doramectin, 50 ppb for selamectin, and 100 ppb for eprinomectin were achieved in spiked sera. Recoveries of avermectins and moxidectin in 500 ppb fortified sera fell between 61 and 89% (+/-5.7-15.7). Analysis of fortified liver gave comparable results with recovery of selamectin of 83-91% +/- 18.3. A complete mass spectral fragmentation pattern of selamectin and affordable screening method for 6 macrolide endectocides are reported. Method comparison for salt treatment and solid-phase extraction of fortified samples is discussed.