Microbial models of soil metabolism: biotransformations of danofloxacin.

Danofloxacin is a new synthetic fluoroquinolone antibacterial agent under development for exclusive use in veterinary medicine. Such use could lead to deposition of low levels of danofloxacin residues in the environment in manure from treated livestock. This study was conducted to evaluate the potential for indigenous soil microorganisms to metabolize danofloxacin. Cultures of 72 soil microorganisms representing a diverse panel of bacteria, fungi and yeast were incubated with danofloxacin mesylate substrate and samples analyzed periodically by high performance liquid chromatography for loss of danofloxacin and formation of metabolites. Some samples were further analyzed by liquid chromatography-mass spectrometry and mass spectrometry to confirm metabolite identification. Twelve organisms, representing eight different genera, biotransformed danofloxacin to metabolites detectable by the chromatographic methods employed. Two Mycobacterium species, two Pseudomonas species, and isolates of Nocardia sp, Rhizopus arrhizus and Streptomyces griseus all formed N-desmethyldanofloxacin. The formation of the 7-amino danofloxacin derivative, 1-cyclopropyl-6-fluoro-7-amino-4-oxo-1,4-dihydroquinoline-3-carboxylic acid by cultures of Candida lipopytica, Pseudomonas fluorescens, two Mycobacterium species and three Penicillium species demonstrates the propensities of these cultures to completely degrade the piperazine ring. At least two additional and unidentified metabolite peaks were observed in chromatograms of Aspergillus nidulans and Penicillium sp cultures. Radiolabled [2-14C]danofloxacin added to cultures of the fungus Curvularia lunata was apparently mineralized, with approximately 31% of the radiolabel recovered as volatile metabolites after 24 h of incubation, indicating the susceptibility of the quinolone ring to microbial metabolic degradation.

Pharmacokinetics and bioequivalence of parenterally administered doramectin in cattle.

Plasma concentrations of doramectin in 40 cattle dosed by subcutaneous (sc) or intramuscular (i.m.) injection (200 micrograms/kg) were compared to assess the bioequivalence of the two routes of administration. Peak concentration (Cmax), and areas under the concentration curve (AUC0-infinity) were determined from plasma concentrations. Animals treated by the sc route showed a mean AUC0-infinity of 457 +/- 66 ng.day/mL (+/- SD) and a mean Cmax of 27.8 +/- 7.9 ng/mL. Results from the i.m. treatment group showed a mean AUC0-infinity of 475 +/- 82 ng.day/mL and a mean Cmax of 33.1 +/- 9.0 ng/mL. Absorption constants (ka) determined by modelling were 0.542 +/- 0.336 day-1 after sc administration and 0.710 +/- 0.357 day-1 after i.m. administration. The 90% confidence limits on the difference between mean AUC0-infinity values for the sc and i.m. groups fell within 20% of the mean value for the subcutaneous group. Cmax was somewhat greater for the i.m. route. The 90% confidence limits on the difference in mean In(Tmax +1) also fell within 20% of the mean sc value. Based on this analysis, bioequivalence of the sc and i.m. formulation has been established.