ABSTRACT
Tilmicosin is a novel macrolide antibiotic developed for exclusive use in veterinary medicine. The first tilmicosin-containing product was approved to treat bovine respiratory disease associated with pasteurellae. The development of antimicrobial susceptibility testing guidelines for tilmicosin was predicated on the relationship of clinical efficacy studies that demonstrated a favorable therapeutic outcome, on pharmaco-kinetic data, and on in vitro test data, as recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The NCCLS-approved breakpoints for the MIC dilution testing are resistant > or = 32 micrograms/ml, intermediate 16 micrograms/ml, and susceptible < or = 8 micrograms/ml. The zone of inhibition interpretive criteria for disk diffusion testing with a 15-micrograms disk are resistant < or = 10 mm, intermediate 11-13 mm, and susceptible > or = 14 mm.
Subject(s)
Anti-Bacterial Agents/pharmacology , Cattle Diseases , Macrolides , Pasteurella Infections/veterinary , Pasteurella/drug effects , Tylosin/analogs & derivatives , Animals , Anti-Bacterial Agents/therapeutic use , Cattle , Erythromycin/pharmacology , Mannheimia haemolytica/drug effects , Mannheimia haemolytica/isolation & purification , Microbial Sensitivity Tests , Pasteurella/isolation & purification , Pasteurella/pathogenicity , Pasteurella Infections/drug therapy , Pasteurella multocida/drug effects , Pasteurella multocida/isolation & purification , Predictive Value of Tests , Reproducibility of Results , Tylosin/pharmacology , Tylosin/therapeutic useABSTRACT
Quality control guidelines for tilmicosin, a novel veterinary-use-only macrolide, were developed in a multi-laboratory study according to established National Committee for Clinical Laboratory Standards (NCCLS) procedures (M23-T2). Tilmicosin was incorporated into Sensititre plates for broth microdilution endpoint testing and into two lots of 15-micrograms disks for Kirby-Bauer agar disk diffusion testing. One common lot and five unique lots of Mueller-Hinton media were used. (Broth was cation adjusted, and agar was supplemented with 5% defibrinated sheep blood.) Bacteria used for reference strains included Pasteurella haemolytica 128K, Pasteurella multocida ATCC 43137, and Staphylococcus aureus ATCC 29213 (microdilution) and ATCC 25923 (disk). Replicate tests were conducted. Disk diffusion and broth microdilution quality control ranges are proposed.
