Stability and Blood Level Determinations of Cefaclor, a New Oral Cephalosporin Antibiotic

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Cefaclor solutions in pH 2.5 and 4.5 buffers contained at least 90% of their initial activity after 72 h at 4°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°C. After 72 h at 25°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°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°C, a 51% loss when incubated for 6 h at 25°C, and a 48% loss when incubated for 2 h at 37°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.

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