Evaluation of the Chemical Integrity of Beta-Lactam Antibiotics by Iodine-Based Assay

Abstract

One of the major problems associated with the therapeutic application of β-lactam antibiotics is their significant instability [1]-[3]. Analogs from that group are easily degraded in aqueous solu-tions and in solid state, which happens predominantly as a result of β-lactam ring chemical de-gradation. Because of this, the chemical integrity of β-lactam antibiotics must be closely monitored to meet FDA requirements. The original iodometric method based on visual detection of the end products of beta-lactamase hydrolysis that has been used to test beta-lactamase activity [4] was modified to quantitatively assess the amount of degraded product in amoxicillin. A UV-visible spectrophotometric method has been used, focusing on the ability of the products from the de-gradation of β-lactam analogs to absorb iodine from bulk solution, resulting in a significant reduc-tion in the absorption spectra. Amoxicillin trihydrate tablets with different expiration dates and amoxicillin samples pre-loaded with known amounts of degraded amoxicillin have been used to generate a calibration curve and quantify the presence of degraded materials. Results show that the changes in the absorption spectra of iodine reagent directly correlate with the fraction of de-graded β-lactam antibiotics, such as amoxicillin, in commercial products. The proposed assay might be as close as one step from simpler and cheaper methods of quantitative analysis of de-graded β-lactam analogs, with estimated sensitivity in the range of 1% -2%, which is better than the current FDA requirements.