Disposition of norfloxacin in broiler chickens and turkeys after different methods of oral administration.

Norfloxacin was administered orally to chickens and turkeys at 15 mg/kg body weight by pulse dosing at 24 h intervals and by continuous dosing at 100 mg/L in drinking water for five days. Blood samples were taken serially. Plasma norfloxacin concentrations were determined by high-performance liquid chromatography. The plasma norfloxacin concentrations increased slowly during continuous dosing and reached the MIC(90) (250 ng/mL) for Gram-negative pathogens by 12 h in chickens and 18 h in turkeys. The steady-state plasma concentration was attained in 36 h and remained at approximately 776.67+/-33.23 ng/mL in chickens and 682.50+/-28.55 ng/mL in turkeys. After pulse dosing, the plasma norfloxacin concentrations increased rapidly and exceeded the MIC(90) at 2 h in both species and remained above MIC(90) for 8 h in chickens and 6 h in turkeys. Pulse dosing provided half the steady-state concentration that was achieved by continuous dosing, 365.32+/-39.31 ng/mL in chickens and 306.03+/-32.26 ng/mL in turkeys, during the dosing interval of 24 h. Data for daily pulse dosing suggested that every administration corresponded to a single, daily repeated bolus administration although pulse dosing produced higher plasma concentrations more readily. Continuous and pulse dosing are both rational for the administration of norfloxacin to flocks of chickens and turkeys. We recommend that treatment be commenced with a pulse oral dose administered over a 4 h period and maintained by continuous oral medication for three to five consecutive days.