FIG. 2.

Left panel, effect of diluting deproteinized plasma in water on cefepime degradation. Samples were serially diluted in water before addition of cefepime (100-mg/liter final concentration) and incubation at 37°C. Symbols represent no dilution (Δ) and fourfold (+) and 16-fold (×) dilutions. The resulting degradation rates for these conditions were 0.407, 0.068, and 0.008 h⁻¹, respectively. Further dilutions of plasma resulted in nonmeasurable degradation over the experimental time frame. Right panel, effect of temperature on the degradation of cefepime in deproteinized human plasma. Samples containing a final cefepime concentration of 100 mg/liter were incubated at 4°C (×), 20°C (+), and 37°C (Δ). The degradation rates for these kinetics were 0.0059, 0.062, and 0.31 h⁻¹, respectively. Inset, according to the Arrhenius law, the energy of activation computed from these constants was 20,520 cal/mol.