Development of a microbiological assay to determine the potency of ceftiofur sodium powder

Ceftiofur sodium is a third-generation broad-spectrum cephalosporin antibiotic, formulated as an intramuscular injection, that is approved for use in pigs, cattle, poultry, and dogs. The present work reports a method to quantify ceftiofur in powder for injection by comparing the cylinder plate assay and the liquid chromatographic (LC) method. The assay is based on the inhibitory effect of ceftiofur upon the strain of Micrococcus luteus ATCC 10240 used as the test microorganism. Ceftiofur sodium at concentrations ranging from 2.0 to 8.0 microg/mL can be measured in powder for injection. A prospective validation showed that the method is linear (r2 = 0.9998), with precise relative standard deviation (RSD) of 0.8% for product A (Excenel; Pharmacia and Upjohn Co., Kalamazoo, MI) and of 0.6% for product B (Topcef; Eurofarma Lab. Ltda, São Paulo, Brazil), with intermediate precision; between-day RSD = 1.0 and 1.1%, between-analyst RSD = 0.8 and 0.8% for products A and B, respectively and accurately. The comparison between bioassay and LC by analysis of variance and Student's t-test showed no significant difference among methodologies. The results demonstrated the validity of the proposed bioassay that is simple and a useful alternative methodology for analysis of ceftiofur in routine quality control.