Avermectin's pharmacokinetic profiles significantly affected by important factors, such as species, age, sex and physiological condition of the animal, aplication route and formulation of drug, nutrition, intra-species and interspecies variatons, differences at metabolism or elimination process^8-10. Avermectins has less soluble ratings in water and highly soluble in oil¹¹. Due to high soluble rating in oil, adipose tissue has been served as drug storage. High proportion fat soluble of this group of drugs; has a large volume of distribution and accumulated at liver and adipose tissue to be eliminated slowly².

There is no data on the kinetic disposition of selamectin following topical administration in sheep and goats. Thus, the aim of study was to determine plasma concentrations and some pharmacokinetic profiles during 35 days after administration topically selamectin used widely at animals to treat ecto and endoparasitic diseases and a new product avermectin derivation with doses of 12 mg/kg at sheep and goats.

Analytical procedures: The plasma concentration of selamectin was analysed by high performance liquid chromatography (HPLC) according to the method of Sutra et al.¹² and Walker and Fenner¹³ using HPLC system (Schimadzu LC-20 AT, Japan). The mobile phase¹³ consisted of acetonitrile- watertetrahidrofuran (68:17:15, v/v/v) and at a flow rate of 1 mL/minute. A C18 analytical column (5 μ; 250x4.6 mm, Phenomenex, UK) was used for analysis. Fluorescence detection was at an excitation wavelength of 360 nm and emission wavelength of 450 nm. Each sample run was 15 min.

Pharmacokinetic and statistical analysis of data: The plasma concentration-time data after administration of drug for each animal were created by using WinNonlin® 4.1 software programme (Scientific Consulting Inc., USA). Pharmacokinetic parameters for each animal were analyzed using topical route of administration and non-compartmental model. SPSS software (for Windows 11.5) was used for the statistical analysis. Mann Whitney U-test was used to test for between species differences in plasma concentration and some pharmacokinetic parametres. Results mean ± standart deviation (SD) were expressed and mean values were considered statistically was different at P<0.05.

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Table 1: Mean (±SD) pharmacokinetic parameters of selamectin in sheep and goats following topical administration at a dose rate of 12 mg/kg (n: 20)

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Figure 1: Mean (±S.D.) plasma concentration time profile after topical administration selamectin at a dose of 12 mg/kg in sheep

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Figure 2: Mean (±S.D.) plasma concentration time profile after topical administration selamectin at a dose of 12 mg/kg in goats

As a result of the analysis, for sheep mean plasma concentration, C_max, AUC, MRT and T_max values determined as 1427.27±90.52 pg/mL, 4.78±0.61ng/mL, 810.35±115.95 ng.h/mL, 10.86±0.89 days and 72 hours, respectively and for goats plasma concentration, C_max, AUC, MRT and T_max values determined as 1195.03±70.81 pg/mL, 3.27±0.52 ng/mL, 664.42±72.62 ng.h/ml, 10.46±0.74 days and 72 hours, respectively.

In a study conducted by Sarasola et al.^15, after topically administration of selamectin C_max and T_max values were determined as 86.5±34.0 ng/mL and 3 days in dogs, respectively and for cats 5513±2173 ng/mL and 15 hours, respectively.

In a study conducted by Dupuy et al.^1, after topically administration of selamectin with 6 mg/kg dose C_max, AUC, MRT, T_max values determined as 12.72±5.13 ng/mL, 192.08±63.85 ng.d/mL, 12.55 days, 4.86±3.56 days at male dogs, respectively and 22.65±11.95 ng/mL, 370.97±146.87 ng.d/mL, 12.55 days, 5.2±1.87 days for female dogs, respectively.

As a result, selamectin was topically administired for treatment and control of parasitic diseases of sheep and goats, mean plasma concentration, C_max and AUC values were found higher in sheeps compared to goats and no significant difference were identified between goats and sheep for MRT and T_max values.

This study has contributed to pharmacokinetic values of selamectin at sheep and goats. We believe that new studies must be conducted for dose and dose limits, planned a variety of pharmacokinetic studies, revealing drug interactions and determination of residual period of selamectin at sheep, goat and cattle.

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