Biomedical subjects
Publications and source records attributed to J V Dietz.
Computational procedures specified for the FDA single-dose diffusion assay for antibiotics may cause substantial error in estimated sample potency. An unrecognized mistake in reference solution concentration is the source of error. It is caused by correcting responses from standard and sample plates differently. The error can be avoided by correcting both standard and sample responses to the observed reference response.
Cefaclor solutions in pH 2.5 and 4.5 buffers contained at least 90% of their initial activity after 72 h at 4 degrees C. Samples in pH 6.0, 7.0, and 8.0 buffers contained 70, 46, and 34%, respectively, of their initial activity after 72 h at 4 degrees C. After 72 h at 25 degrees C, samples prepared with pH 2.5, 4.5, 6.0, 7.0, and 8.0 buffers contained 95, 69, 16, 5, and 3%, respectively, of their initial activity. After 72 h at 37 degrees C, cefaclor solutions in pH 2.5 buffer contained 80% of the initial activity, whereas samples prepared in pH 4.5, 6.0, 7.0, and 8.0 buffers contained less than 20%. Laboratory-prepared plasma and serum samples showed an 8% loss in activity when incubated for 6 h at 4 degrees C, a 51% loss when incubated for 6 h at 25 degrees C, and a 48% loss when incubated for 2 h at 37 degrees C. Clinical samples demonstrated a similar stability pattern. Degradation rates for cefaclor in commercially prepared serum increased from 4- to 10-fold in comparison to rates obtained when samples were made in human serum freshly prepared in our laboratory. Consequently, serum standards should be made in freshly prepared human serum.