ANALYSIS OF THE SAFETY AND TOLERANCE OF A NOVEL ORAL SUSPENSION WITH IVERMECTIN IN SHEEP

Ivermectin is a macrocyclic lactone with a wide therapeutic range, being active against many species of parasitic nematodes and arthropods in animals. The mechanism of action of Ivermectin consists of paralysis, death and elimination of these pathogens by interfering with neurotransmitters at the level of GABA receptors and glutamate-sensitive channels of chlorine. The selectivity of the pharmacological action of Ivermectin is mammalian specific, being correlated with the lack of target receptors for glutamate and the limitation of GABA encephalic receptors. In dogs, neurointoxications with Ivermentin are possible, due to stimulation of GABA receptors, with extremely high encephalic concentrations compared to liver and plasma concentrations. The aim of this research was to monitor the health of a sheep batch after oral administration of two suspensions of Ivermectin, in order to evaluate the bioequivalence, safety and tolerance of the proposed test formula for interchanges in sheep antiparasitic therapy. The main clinical and paraclinical health indices were also monitored in a sample of native sheep (no=36), during the bioequivalence testing of two formulas with Ivermectin, using a single-center, randomized, single-dose, two-sequence protocol, two periods and a break of 2 weeks. The study required clinical, hematological (with the Abacus junior Vet automatic analyzer and Dia-Quick Panoptic colored smears) and blood biochemistry (with the VetScan automatic analyzer and Large Animal Profile kits). These were grouped into the following four sets of assessments: initial (for selection of healthy animals), pre-dose (before product administration), post-dose (on the day of product administration) and final. Clinical and paraclinical examinations were also based on the detection, characterization, and possible adverse reactions, in order to evaluate the safety and tolerance of the investigated products. Bioequivalence testing required the collection of serial blood samples (on EDTA), pre- and post-dose (6 mL/10 kg), at different time intervals (0-480 hours), from each subject, during the two phases of the study. The freshly collected blood samples were centrifuged for 10 minutes at 2000 rpm, and from the obtained plasma, Ivermectin concentrations were determined by using liquid chromatography method coupled with mass spectrometry (LC-MS/MS). Plasma concentration analysis was the basis for determining the pharmacokinetic parameters and assessing the bioequivalence of test/reference (T/R) formulas. By using a non-compartmental model, the primary pharmacokinetic parameters (C-max, T-max and AUC) have been extrapolated to infinity, and the bioequivalence is confirmed based on the evaluation of 90% confidence intervals (CI) of C(max )and AUC(last). We also used the Tukey and Dun biostatistic tests to calculate the mean, median, standard deviation, standard error, 95% CI and probability index "p". In the clinical and hemato-biochemical examinations, no subjects presented adverse side effects, these developments revealing a good tolerance and therapeutic safety of oral suspensions with Ivermectin in sheep. The maximum plasma concentrations of Ivermectin reached very close levels, the mean values for the T/R ratio being 41.22 (+/- 8.7)/42.18 (+/- 10.46) ng/mL. In this respect, the evolution of the average values of the main pharmacokinetic parameters, which for the T/R groups, showed statistically insignificant differences in the case of T-max (17.5/18.33 hours) and T-1/2 (84.29/91.04 hours), indicating absorption and the slow elimination of Ivermectin after digestive administration. The analysis of the values obtained in the calculation of CI 90%, for the T/R ratio, of the C-max (0.92-1.04), AUC(last) (0.86-1.06) and T-1/2 (0.85-1.05), revealed statistically insignificant variations, with the framing of the average values in the reference interval (0.8-1.25), indicating the bioequivalence of the two suspensions with Ivermectin. In conclusion, the investigation of the two suspensions,proven to be bioequivalent and interchangeable in ovine therapy, outlined a good tolerance and therapeutic safety, their pharmacokinetic profiles indicating a slow absorption rate of Ivermectin and a sufficiently long contact time with gastrointestinal parasites.