PARENT SESSION

TP5 Ecotoxicity and Environmental Chemistry Antibiotics
Room 17A/B, Level 4
2:10 PM - 5:30 PM, Tuesday, 11 November 2003
Chair: Aga, Diana ,

(283) Environmental Fate of the Veterinary Antimicrobial Ceftiofur (Excenel®, Naxcel®).

Smolenski, Walter¹, Hummel, Bernard¹, Lesman, Steven¹, ¹ Pfizer Animal Health, Kalamazoo, MI, USA

ABSTRACT- Ceftiofur (CF) is a late-generation cephalosporin used solely for veterinary purposes and is the active ingredient in Excenel® and Naxcel®. The fate of antibiotics excreted by food animals is of environmental concern. Degradation of active molecules provides less opportunity for detrimental environmental effects to occur. Ceftiofur residues excreted from cattle are inactive in feces but active in urine. Urine residues become inactive when mixed with feces. Ceftiofur is light sensitive, and aqueous hydrolysis occurs with a 8 day half-life (t) at pH 7. Ceftiofur has a K_oc in soil of 276. Methods: For biodegradation studies, ¹⁴C-Ceftiofur was added to 4 soils at 5 ppm and incubated at 20°C. Mineralization to ¹⁴CO₂ was measured, ceftiofur and production of metabolites analyzed by LC/MS. An assay that converted active metabolites including ceftiofur to a common metabolite, desfuroylceftiofur (DFC) and then stabilized by conversion to DFC-acetamide (DCA) was used to measure total active residue. Results: The t of ceftiofur and active metabolites (DCA) ranged from 0.1 to 1.9 h. and 0.2 to 2.4 h, respectively. All radioactive metabolites were transient without accumulation. The ultimate fate of the carbon in the molecule was mineralization to ¹⁴CO₂. At only 3 days ¹⁴CO₂ recovery in 3 soils was >12%, and by 120 days mean recovery increased to 54%. The overall mass balance of ¹⁴CO₂, soil-bound and extractable radioactivity was 99%. Conclusion: Ceftiofur is rapidly inactivated and transformed in aerobic soil systems, and ultimately mineralized to CO₂. All metabolites detected were transient and did not accumulate. With the short residence time of the molecule and its metabolites in soil and other environments, the likelihood for environmental effects to occur is low.

Key words: biodegradation, antibiotic, ceftiofur, soil