Pharmacokinetics and clinical assessment of amoxicillin for the control of necrotic enteritis in broiler-breeders under field conditions

Abstract

Necrotic enteritis (NE) is an acute clostridium infection characterised by sudden onset, high mortality and severe necrosis of intestinal mucosa. The present study was conducted to clinically assess the efficacy of amoxicillin to control naturally occurring NE caused by Clostridium perfringens type A in broiler-breeders and to further support the clinical outcome of drug administration with evidence of efficacy based on the pharmacodynamic/pharmacokinetic correlation. A flock of 34,000 broiler-breeders exhibited an abrupt increase in mortality and a mild decrease in egg production, together with a reduction in body weight (BW). No signs of gross lesions were apparent, except a necrotic pseudomembrane covering the intestinal mucosa. Microbiological cultures from the intestine and PCR revealed the presence of Clostridium perfringens type A. After the administration of an amoxicillin compound (Animox (R) 500 water soluble powder50%, PHARMAQUA) at the dose of 20 mg kg(-1) BW diluted in the drinking water for five consecutive days, the flock recovered normally, the production data reached levels prior to induction of the disease and the intestine tissue was rapidly improved. The minimal inhibitory concentrations (MIC) of the isolated pathogen was determined and a pharmacokinetic study was performed under field conditions. The pharmacodynamic/pharmacokinetic correlation revealed a C-max/MIC ratio of 167.9, well above the value of 10-12 for a bactericidal and eliminatory effect to be expected. Furthermore, the AUC/MIC ratio was 1383.2, supporting the efficacy of the drug even if used in immunocompromised patients. Based on both clinical and pharmacological evidence amoxicillin can be used for the control of NE during an outbreak.