Evaluation of therapeutic and prophylactic effectiveness of levofloxacin in experimental colibacillosis of chickens with regard to infecting dose

Abstract

The goal of the present research was to investigate therapeutic and prophylactic effectiveness of levofloxacin following experimental challenge of chickens with varying doses of Escherichia сoli namely 1 minimum lethal dose (DLM) and 4 minimum lethal doses (DLM). We conducted two experiments on two-day-old Hisex Brown chickens. For the first experiment we used 6 groups of chicks (n = 25, in each group). The drug was administered via drinking water (with free access) 24 hours before the challenge. Chicks of Groups 1 to 4 received levofloxacin via drinking water at concentrations 50 mg/L, 100 mg/L, 200 mg/L and 300 mg/L for 5 days. Group 5 was control, Group 6 was intact. The chicks were challenged with 1.5 х 108 E. сoli bacterial cells per 0.5 mL (1 minimum lethal dose (DLM)) intraperitoneally. The second experiment was conducted similarly but the infecting dose was increased by 4 times (4 minimum lethal doses (DLM)).Administration of levofloxacin at concentration 300 mg/L both in the first experiment, when the infecting dose was 1 minimum lethal dose, and in the second experiment, when the infecting dose was 4 minimum lethal doses, proved that the drug has the same high therapeutic and prophylactic effectiveness of 96 %. Administration of the drug at concentration 200 mg/L showed 100 % effectiveness in the first experiment. But in the second experiment levofloxacin at the same concentration ensured survival of only 88 % of the challenged chicks. When the drug was administered at concentration 100 mg/L we observed reliable change in indices. Accordingly in the first experiment 88 % of the chicks survived. In the second experiment, when the infecting dose increased to 4 minimum lethal doses, only 52 % of the chicks survived. Administration of levofloxacin at concentration 50 mg/L did not show significant therapeutic effect.