Enrofloxacin is a synthetic, broad spectrum antimicrobial substance, belonging to the fluoroquinolone group of antibiotics.

Enrofloxacin is bactericidal in action with activity against a wide range of Gram positive and Gram negative bacteria and mycoplasmas. The mechanism of action of the quinolones is unique among antimicrobials - they act primarily to inhibit bacterial DNA gyrase, an enzyme responsible for controlling the supercoiling of bacterial DNA during replication. Resealing of the double stranded helix is inhibited resulting in irreversible degradation of the chromosomal DNA. The fluoroquinolones also possess activity against bacteria in the stationary phase by an alteration of the permeability of the outer membrane phospholipid cell wall.

Molecular resistance to fluoroquinolones has been observed to arise from two principal sources, (i) alteration to DNA gyrase or topoisomerase IV and (ii) alterations in drug permeability of the bacterial cell. Both mechanisms lead to a reduced susceptibility of the bacteria to fluoroquinolones. Clinical resistance is dependent on several mutations accumulating in a step-wise manner. The pharmacokinetics of enrofloxacin are such that oral and parenteral administration leads to similar serum levels. Enrofloxacin possesses a high distribution volume. Tissue levels 2-3 higher than that found in the serum, have been demonstrated in laboratory animals and target species. Organs in which high levels can be expected are the lungs, liver, kidney, skin, bone and lymphatic system. Enrofloxacin also distributes into the cerebrospinal fluid, the aqueous humour and the foetus in pregnant animals.

After an intravenous dose of 5 mg enrofloxacin per kg body weight (bw) to lactating dairy cattle, the total systemic exposure over the dosing interval of 24 h was at 7.1 mg*h/L. In cattle serum, approximately 30% of drug exposure (2.31 mg*h/L) consisted of ciprofloxacin, the active metabolite of enrofloxacin. The drug was well distributed into the body compartments (Venro = 1.5 L/kg, Vcipro = 8.51 L/kg). Total body clearance was 0.71 L/h/kg. In milk, most of drug activity consisted of ciprofloxacin. Overall drug concentrations peaked at 4.1 mg/kg two hours after treatment. Overall drug exposure over 24 h was

22.1 mg*h/L. The actives were eliminated from milk with a mean exposure half-life of 2.8 h.