Validation of erythromycin microbiological assay using an alternative experimental design

The agar diffusion method, widely used in antibiotic dosage, relates the diameter of the inhibition zone to the dose of the substance assayed. An experimental plan is proposed that may provide better results and an indication of the assay validity. The symmetric or balanced assays (2 x 2) as well as those with interpolation in standard curve (5 x 1) are the main designs used in the dosage of antibiotics. This study proposes an alternative experimental design for erythromycin microbiological assay with the evaluation of the validation parameters of the method referring to linearity, precision, and accuracy. The design proposed (3 x 1) uses 3 doses of standard and 1 dose of sample applied in a unique plate, aggregating the characteristics of the 2 x 2 and 5 x 1 assays. The method was validated for erythromycin microbiological assay through agar diffusion, revealing its adequacy to linearity, precision, and accuracy standards. Likewise, the statistical methods used demonstrated their accordance with the method concerning the parameters evaluated. The 3 x 1 design proved to be adequate for the dosage of erythromycin and thus a good alternative for erythromycin assay.