In Vitro Activity of Difloxacin against Canine Bacterial Isolates

Abstract

Abstract. The in vitro activity of difloxacin against canine bacterial isolates from clinical cases was studied in the United States and The Netherlands. Minimal inhibitory concentrations (MIC), the postantibiotic effect, the effect of pH on antimicrobial activity, and the bacterial killing rate tests were determined according to standard techniques. The MICs of American and Dutch isolates agreed in general. The MICs of the American gram-negative isolates ranged from 0.06 to 2.0 g/ml, and the MICs of the Dutch gram-negative isolates ranged from 0.016 to 8.0 g/ml. A few European strains of Proteus mirabilis and Klebsiella pneumoniae had relatively high MICs. Bordetella bronchiseptica also was less susceptible to difloxacin. The MICs of the American grampositive cocci ranged from 0.125 to 4.0 g/ml, and the MICs of Dutch isolates ranged from 0.125 to 2.0 g/ ml. Difloxacin induced a concentration-dependent postantibiotic effect that lasted 0.2-3 hours in cultures with Escherichia coli, Staphylococcus intermedius, Streptococcus canis, Proteus spp., and Klebsiella pneumoniae. There was no postantibiotic effect observed against canine Pseudomonas aeruginosa. Decreasing the pH of the medium increased the MIC of Proteus mirabilis for difloxacin. The MICs of Escherichia coli and Klebsiella pneumoniae were lowest at neutral pH and were slightly increased in acid or alkaline media. At a neutral pH, most tested bacterial species were killed at a difloxacin concentration of 4 times the MIC. Similar results were obtained when these same bacteria were tested against enrofloxacin. A Klebsiella pneumoniae strain in an acidic environment was readily killed at difloxacin or enrofloxacin MIC, but at neutral pH the drug concentration had to be raised to 4 times the MIC for a bactericidal effect. After 24 hours of incubation at pH 7.1, difloxacin and enrofloxacin had similar bactericidal activity for all bacteria tested except Staphylococcus intermedius. Against S. intermedius, difloxacin was more bactericidal than enrofloxacin.Difloxacin HCl is a difluorinated quinolone, 1-pfluorophenyl-6-fluoro-1,4-dihydro-4-oxo-7-(4-methyl-1-piperazinyl)-3-quinolone-carboxylic acid hydrochloride, marketed for use in veterinary medicine in the United States and Europe for the treatment of canine bacterial infections in the urinary tract, the respiratory tract, and the skin. Difloxacin is an amphoteric molecule with relatively nonpolar characteristics for a quinolone. 5 Difloxacin HCl is rapidly absorbed following oral administration. Like other fluoroquinolones, difloxacin exhibits bactericidal activity primarily by binding to the A subunit of bacterial DNA-gyrase. 5 However, there is also the possibility that difloxacin might also bind to and inhibit topoisomerase. 10 Difloxacin's potency against gram-negative bacteria is similar to that of orbifloxacin and enrofloxacin, 2 other fluorinated quinolones marketed for the treatment of canine bacterial infections. Difloxacin differs from Received for publication June 28, 1999. these 2 compounds by it...

Post-antibiotic effect of orbifloxacin against Escherichia coli and Pseudomonas aeruginosa isolates from dogs

“…In previous studies, van den Hoven et al [3] reported that difloxacin had PAEs of 0.5 h for E. coli and -0.4 h for P. aeruginosa . Spreng et al [2] reported PAEs for marbofloxacin that ranged from 0.6 to 0.9 h for E. coli .…”

In vitro and in vivo pharmacodynamic properties of the fluoroquinolone ibafloxacin

“…For example, in the present studies, MIC determinations were carried out once using Iso‐sensitest as the growth medium, whereas MIC was performed at least in duplicate using Mueller Hinton broth for the other fluoroquinolones. Nevertheless, despite variations in media and in vitro methods, ibafloxacin tends to present similarities in terms of efficacy as compared with enrofloxacin, orbifloxacin, difloxacin and marbofloxacin marketed for use in companion animals (van den Hoven et al ., 2000; Walker, 2000).…”

“…At present this information is lacking in veterinary medicine where the fluoroquinolones are relatively new antimicrobial agents. Four other fluoroquinolones, enrofloxacin, marbofloxacin, orbifloxacin and difloxacin, are used routinely in companion animals (Brown, 1996; Ihrke et al ., 1999; van den Hoven et al ., 2000; Walker, 2000; Heinen, 2002).…”

Pharmacokinetics and milk penetration of difloxacin after a long-acting formulation for subcutaneous administration to lactating goats

“…aureus in up to 37% of subclinical mastitis isolates (Silva et al, 2004). Efficacy of difloxacin treatment of mastitis in goats has not been tested, but the efficacy of the drug against respiratory infections of lambs (Mavrogianni and Fthenakis, 2005), calves (Olchowy et al, 2000), dogs (van den Hoven et al, 2000), and poultry (Kempf et al, 1998) Antimicrobial drugs that act predominantly by concentration-dependent mechanisms generally exert significant postantibiotic sub-MIC effects. Such drugs continue to inhibit bacterial growth for a period of hours after they have been completely removed from the system.…”