Penetration of enrofloxacin into the nasal secretions and relationship between nasal secretions and plasma enrofloxacin concentrations after intramuscular administration in healthy pigs

The pharmacokinetic behaviour of enrofloxacin (ENRO) in plasma and nasal secretions of healthy pigs was investigated, after a single-dose intramuscular administration of 2.5 mg/kg body weight of the drug. Blood samples and nasal secretions were collected at predetermined times after drug administration. Concentrations of ENRO and its active metabolite ciprofloxacin (CIPRO) were determined in plasma and nasal secretions by high-performance liquid chromatography (HPLC). CIPRO was not detected probably because we investigated young weaned pigs. The data collected in 12 pigs for ENRO were subjected to noncompartmental analysis. In plasma, the maximum concentration of drug (C-max), the time at which this maximum concentration of drug (T-max) was reached, the elimination half-life (t(beta)(1/2)) and the area under the concentration vs. time curve (AUC) were, respectively, 694.7 ng/mL, 1.0 h, 9.3 h and 8903.2 ng h/mL. In nasal secretions, Cmax, Tmax, t(beta)(1/2) and AUC were, respectively, 871.4 ng/mL, 2.0 h, 12.5 h and 11 198.5 ng.h/mL. In a second experiment conducted in 10 piglets, the relationship between concentrations of ENRO measured in the plasma and the nasal secretions has been determined following single-dose intramuscular administration of 2.5, 10 or 20 mg/kg body weight of the drug. It has been demonstrated that, among several variables, i.e., (1) the dose administered, (2) the time between intramuscular injection and blood sampling, (3) the age, (4) the sex, (5) the animal body weight and (6) the plasma concentration of the drug, only the latter influenced significantly the ENRO concentration in nasal secretions. Practically, using a generalized linear mixed model, ENRO concentrations in the nasal secretions (mu g/mL) can be predicted taking into account the ENRO concentrations in plasma (mu g/mL), according to the following equation: ENROnasal secretion 1.94 ENROplasma - 0.24.