The assay of antimicrobial compounds

The earliest antibiotic assays evolved from attempts to qualitatively demonstrate antimicrobial activity in biological fluids. The need for rapid, selective, accurate assays of antibiotics present in blood arises from the fact that many potentially toxic, commonly used antibiotics have narrow toxic: therapeutic ratios; no single dosage regimen can insure adequate therapeutic levels that are not toxic, because of individual variation in excretory patterns and in susceptibility of infecting bacteria. This need for rapid quantitative information about the serum antibiotic concentration can be met by agar diffusion assays, enzymatic assay, or radioimmunoassay. Other assay techniques less commonly used to meet this clinical need are both dilution assay, turbidimetric assay, potentiometric assay, and chemical assay. Details for one agar diffusion assay are presented, as well as principles and references for other techniques.