Concentraciones de florfenicol en leche de vacas en lactancia postratamiento por vía intramuscular o intramamariaJohn Ruiz B, ABSTRACTObjective. To determine the florfenicol concentration in bovine milk after intramuscular or intramammary administration to establish the optimum withdrawal time, therapeutic efficacy, and its influence on milk yield. Materials and method. Twelve healthy lactating Holstein cows were selected from the University of Antioquia's teaching dairy herd (Colombia), were randomly assigned to a control (n=6) group or florfenicol (n=6) group that received 20 mg/kg of florfenicol by intramammary and intramuscular routes, with a 15 days washout period between treatments. Results. The Tmax and Cmax for the intramuscular route were 6 hours and 2.86 mg/L respectively. The Tmax and Cmax for the intramammary route, were estimated at 0 hour and about 20000 mg/L respectively by extrapolated from regression line. The florfenicol elimination phase in milk had an average half-life of elimination (t½) of 19.8 hours and 4.9 hours for intramuscular and intramammary administration, respectively. The therapeutic efficacy only was reached by intramammary route, when minimal inhibitory concentration (M.I.C.) of florfenicol by Stahphylococcus aureus, was used as reference value. There was no statistically significant difference in milk yield between treated and non-treated cows. Conclusions. According to these results, post-treatment milk withdrawal should be no less than 3 days for intramammary administration, and at least 7 days for intramuscular administration. The therapeutic efficacy only was reached by intramammary route. In addition, there was no statistically significant difference in milk yield between treated and nontreated cows. RESUMENObjetivo. Determinar la concentración de florfenicol en leche bovina después del tratamiento intramuscular o intramamario, para establecer el tiempo de retiro, la eficacia terapéutica, y su influencia sobre la producción láctea. Materiales y métodos. Se seleccionaron doce vacas Holstein en lactancia de la hacienda de Universidad de Antioquia (Colombia). Se asignaron al azar al grupo control (n=6) o al grupo florfenicol (n=6), al cual se le administró 20 mg/kg de florfenicol por vía intramamaria e intramuscular con 15 días de diferencia entre tratamientos. Resultados. La Tmax y Cmax para la vía intramuscular fueron 6 horas y 2.86 mg/L respectivamente. La Tmax y Cmax para la vía intramamaria, fueron estimados como 0 hora y aproximadamente 20000 mg/L respectivamente por extrapolación de la línea de regresión. La fase de eliminación del florfenicol en leche, tuvo una vida media de eliminación (t½) promedio de 19.8 horas y 4.9 horas para la vía intramuscular e intramamaria respectivamente. Cuando la concentración inhibitoria minima (C.I.M) del florfenicol para Stahphylococcus aureus, fue usada como el valor de referencia, la eficacia terapéutica sólo se alcanzó por la vía intramamaria. No existió diferencia estadística significativa entre las producciones lácteas de las v...