pH and temperature effects on the hydrolysis of three beta-lactam antibiotics: Ampicillin, cefalotin and cefoxitin

An understanding of antibiotic hydrolysis rates is important for predicting their environmental persistence. Hydrolysis rates and Arrhenius constants were determined as a function of pH and temperature for three common beta-lactam antibiotics, ampicillin, cefalotin, and cefoxitin. Antibiotic hydrolysis rates at pH 4-9 at 25 degrees C, 50 degrees C, and 60 degrees C were quantified, and degradation products were identified. The three antibiotics hydrolyzed under ambient conditions (pH 7 and 25 degrees C); half-lives ranged from 5.3 to 27 d. Base-catalyzed hydrolysis rates were significantly greater than acid-catalyzed and neutral pH hydrolysis rates. Hydrolysis rates increased 2.5- to 3.9-fold for a 10 degrees C increase in temperature. Based on the degradation product masses found, the likely functional groups that underwent hydrolysis were lactam, ester, carbamate, and amide moieties. Many of the proposed products resulting from the hydrolysis of ampicillin, cefalotin, and cefoxitin likely have reduced antimicrobial activity because many products contained a hydrated lactam ring. The results of this research demonstrate that beta-lactam antibiotics hydrolyzed under ambient pH and temperature conditions. Degradation of beta-lactam antibiotics will likely occur over several weeks in most surface waters and over several days in more alkaline systems. (C) 2013 Elsevier B.V. All rights reserved.