Rapid, precise, turbidometric assay for low levels of ampicillin in serum after single-dose oral administration.

A turbidometric assay is described for the quantitative measurement of ampicillin in serum. Standard curves prepared with known concentrations of ampicillin in serum exhibited acceptable linearity over a concentration range of approximately 0.2 to 1.8 mug/ml. Data are presented to show the excellent precision of the assay and the application of the assay to clinical studies. The advantages of this method over other procedures are discussed. Because of the questionable stability of ampicillin, samples containing known concentrations of ampicillin in serum were assayed after storage for various lengths of time. Serum samples maintained in the frozen state until the time of assay exhibited approximately 12% degradation after 7 days, whereas those samples which were subjected to repeated thawing and refreezing exhibited approximately 25% degradation after the same time interval.