Comparative persistent efficacy of doramectin, ivermectin and fenbendazole against natural nematode infections in cattle.

A study was conducted in Argentina, to investigate the period of protection of a single injection of doramectin administered subcutaneously (s.c.) at 200 micrograms kg-1 (1 ml/50 kg) compared with single treatments of ivermectin (200 micrograms kg-1 s.c.) and fenbendazole (5 mg kg-1 p.o.), against field infections of gastrointestinal parasites of cattle. Eighty-three animals were selected and ranked on the basis of serial fecal egg counts (e.p.g.'s). From this group, three animals were slaughtered before treatment and their lungs, abomasum, small and large intestines, were processed for parasite counts and identification. The remaining 80 animals were allocated in ranked groups of four to a control or one of three treated groups. Animals of the four groups were grazed together in the same pasture for the duration of the study. Treatments were administered on Day 0. Individual fecal samples were collected at weekly intervals for the first 49 days post-treatment and twice a week from Day 52 to Day 84 (end of study). At each collection day fecal samples were pooled for coprocultures. On Day 28 and 56, two animals from each group, previously identified on Day 0, were killed and their parasite burdens determined. The duration of protection of a single injection of doramectin was longer than ivermectin or fenbendazole treatment. On Day 56, the total number of parasites found in doramectin-treated animals was significantly (P < 0.05) lower than parasite burdens found in either ivermectin- or fenbendazole-treated animals. The longer persistent activity of doramectin was expressed by the lower number of adults and L4 stages of Ostertagia ostertagi. Data from this experiment demonstrated the limitations of using fecal egg counts to evaluate the persistent efficacy of anthelmintics. The duration of activity of doramectin was demonstrated more accurately by parasite counts in cattle from each group since decreasing e.p.g.'s were seen in non-medicated animals without changes in total parasite burdens.

Antimicrobial susceptibility of Actinobacillus pleuropneumoniae, Pasteurella multocida and Salmonella choleraesuis isolates from pigs.

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.

In vitro susceptibility of avian Escherichia coli and Pasteurella multocida to danofloxacin and five other antimicrobials.

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.