Danofloxacin is a new fluoroquinolone antibacterial, developed specifically for veterinary use. Its in vitro activity and pharmacokinetic properties have been investigated to assess its potential for use in the therapy of respiratory disease in cattle. The minimum inhibitory concentration of danofloxacin against 90% (MIC90) of contemporary European and North American field isolates of Pasteurella haemolytica, Pasteurella multocida and Haemophilus somnus, the most important bacterial respiratory pathogens of cattle, was 0.125 micrograms/ml. The plasma and lung kinetics of danofloxacin following parenteral administration of 1.25 mg/kg were evaluated in two studies. Danofloxacin was rapidly absorbed following intramuscular and subcutaneous injection and bioavailability was virtually complete (101% and 94% respectively). Plasma concentration profiles of danofloxacin were similar for intramuscular and subcutaneous routes with no significant differences in the area under the plasma concentration-time curves (AUC) following one, three or five consecutive daily doses, although slightly higher peak plasma concentrations were achieved by the intramuscular route. Following intramuscular administration, the mean peak lung concentration of danofloxacin was 4.1 times greater than that of plasma. Similarly, the AUC for lung tissue was 3.7 times greater than that for plasma. These data indicate that danofloxacin should be particularly appropriate for the therapy of bacterial respiratory disease in cattle.

A technique is described for determining the antimicrobial susceptibility of Mycoplasma gallisepticum, using the Sensititre broth microdilution system. Fourteen M. gallisepticum field isolates and one reference isolate (R-strain) were tested in duplicate against seven antimicrobials. Isolates were susceptible to oxytetracycline, furaltadone, and lincomycin/spectinomycin, but not to amoxycillin and apramycin. Susceptibility to erythromycin and tylosin varied. These data are in agreement with those reported by other workers using more traditional methods, but this adaptation of the broth microdilution technique eliminates any variation attributable to the time-consuming preparation of antimicrobial dilutions associated with these methods.

The in vitro susceptibility of 839 isolates of Actinobacillus pleuropneumoniae, 969 isolates of Pasteurella multocida and 104 isolates of Salmonella choleraesuis from pigs to the fluoroquinolone danofloxacin, and eight other commonly used antimicrobial drugs was determined by veterinary diagnostic laboratories in Europe, Japan, South Africa and North America between 1989 and 1991, by using a broth microdilution technique. The minimum inhibitory concentrations of danofloxacin, amoxycillin, ceftiofur, erythromycin, gentamicin, lincomycin, oxytetracycline, spectinomycin and trimethoprim:sulphamethoxazole (ratio 1:19) that prevented the growth of 90 per cent of the bacteria were 0.125, < or = 0.5, < or = 0.125, 8, 8, 32, 32, 64 and < or = 0.25 microgram/ml for A pleuropneumoniae, 0.06, 1, < or = 0.125, 8, 4, 64, 8, 32 and 8 micrograms/ml for P multocida, and 0.125, > 64, < or = 1, > 64, 1, > 64, > 64, 64 and < or = 0.25 microgram/ml for S choleraesuis. These data confirm the high in vitro potency of danofloxacin against field isolates that show significant resistance to several other antibacterial drugs.

The in vitro susceptibility of Escherichia coli and Pasteurella multocida isolated from poultry was determined to danofloxacin, a novel fluoroquinolone, and five other commonly used antimicrobials. A total of 1737 E. coli field isolates and 107 P. multocida isolates were tested by veterinary diagnostic laboratories in Europe, Japan, South Africa, and North America during the period 1989-91. The antimicrobial susceptibility of these isolates was determined using the Sensititre broth microdilution technique. The minimum inhibitory concentrations (MIC) of danofloxacin, furaltadone, lincomycin, oxytetracycline, spectinomycin, and trimethoprim:sulfamethoxazole that prevented growth of 90% of the bacteria were 0.25 > 64, > 64, > 64, > 128, and > 16 micrograms/ml, respectively, against E. coli isolates and 0.25, 64, 64, 16, 128, and 8 micrograms/ml, respectively, against P. multocida isolates. Danofloxacin demonstrated considerable in vitro potency against these important poultry pathogens, many of which showed extensive resistance to the other antimicrobials tested.

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