Modification of the Colorimetric Assay for Chloramphenicol in the Presence of Bilirubin

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Abstract
We recently found that bilirubin interferes with the colorimetric chloramphenicol assay of Kakemi et al. (K. T. Kakemi, T. Arita, and S. Ohashi, Yakugaku Zasshi 82:342–345, 1962). Levels of serum bilirubin alone (4 to 6 mg/dl) resulted in apparent concentrations of chloramphenicol which appear to be in the therapeutic range. Concentrations of serum bilirubin greater than 8 mg/dl resulted in levels of apparent chloramphenicol associated with toxicity (>50 μg/ml). Small amounts of activated charcoal added to the isoamyl acetate extraction step of the assay eliminated this interference by bilirubin.