The aim of the study was to compare the accumulation of β-adrenergic agonist residues clenbuterol (CLB) and salbutamol (SAL) in internal tissues, non-pigmented eyes and hair of laboratory animals repeatedly administered with CLB and SAL during 7 days. Experimental albino guinea pigs (n = 20) were treated with CLB (n = 10) and SAL (n = 10) in anabolic doses of 0.25 and 2.5 mg/kg, whereas the control animal group (n = 10) was left untreated. Methodology validation showed that the ELISA assay to be suitable for β-agonists' semiquantitative determination. The results revealed a significantly higher (P < 0.05) accumulation potential of CLB in comparison with SAL in all investigated tissues. Despite of their lack of pigmentation and the applied dose, the highest residual CLB concentrations were determined in the eyes of the studied animals, followed by their hair, liver, lungs, kidney, heart and adipose and muscle tissue, whereas residual SAL concentrations found in the eyes and hair of the administered animals did not significantly differ (P > 0.05) from those obtained in their internal tissues.

A study of florfenicol (FF) and its metabo- lite florfenicol amine (FFA) in pig cerebrospinal fluid was conducted following repeated intramuscular administration of the original (reference) and a generic veterinary medicinal product (VMP) under the same experimental conditions (20 mg FF/kg body weight, 48-hour interval). Both VMPs are solutions for injection containing FF as an active substance in the concentration of 300 mg/mL and have been authorized in Croatia for use in cattle and pigs. In this study, clinically healthy pigs were randomly divided into three groups. The first group was treated with the reference VMP, the second with the generic VMP, while the third served as the control group. Animals were sacrificed at 216, 288 and 384 hours after the first drug administration. Cerebrospinal fluid samples were analysed by the optimized and validated high-performance liquid chromatography-diode array detector method (HPLC-DAD). The solid-phase extraction (SPE) technique was chosen for sample preparation. The HPLC-DAD method provides good linearity over the concentration range of 0.05 to 5.00 μg/mL for FF and FFA. Limits of detection were 0.0023 μg/mL for FF and 0.0100 μg/mL for FFA. Extraction recoveries of FF were from 86.6% to 111.8%, and of FFA from 91.7% to 98.8%. The SPE-HPLC-DAD method has been demonstrated to be a selective, sensitive and suitable analytical method for the determination of FF and FFA in cerebrospinal fluid. The present study was based on a preliminary study that quantified FF in pig plasma at 216 hours after the first application of reference or generic VMP. However, FF and FFA were not detected in any of the cerebrospinal fluid samples during the experimental period. According to the nature of biological fluids, the SPE-HPLC-DAD method can be suitable for further pharmacokinetic studies of FF in pig plasma and serum after intramuscular administration of VMPs.

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The aim of the present study was to assess the accumulation of ractopamine residues in the hair and ocular tissues of guinea pigs during repeated ractopamine administration and after treatment. The experiment was conducted in 38 guinea pigs (30 treated and eight controls). Treated animals were orally administered ractopamine hydrochloride in a dose of 3.5 mg/kg body mass per day using probes for seven consecutive days. Ractopamine concentration was determined in hair during the treatment (Days 1, 3 and 7) with ractopamine hydrochloride and in ocular tissues and hair on defined days after exposure (Days 1, 10, 20 and 30). Residues were present in hair in high concentrations as early as Day 3 (86.15 ± 87.71 ng/g) and Day 7 (85.25 ± 56.97 ng/g). After exposure, residues were found to persist, having depleted from 68.06 ± 30.54 ng/g on Day 1 to 8.01 ± 2.22 ng/g on Day 30, with a significantly higher concentration in hair in contrast to low residue levels in ocular tissues (1.20-0.34 ng/g). The results of the study pointed to high ractopamine accumulation, even in non-pigmented hair, suggesting hair to be used as a matrix in the control of ractopamine abuse in farm animals because of its many advantages over ocular tissues.