Comparative activity of cefixime and cefaclor in an in vitro model simulating human pharmacokinetics

The dependence of the antibacterial activity of the two oral cephalosporins cefixime and cefaclor on pharmacokinetic properties was investigated in an in vitro model using strains of enterobacteria and a streptococcal strain. In the cultures the course of serum concentrations of the respective antibiotic was simulated. The more rapidly attained (1 h) high peak levels (17.5 µg/ml) of cefaclor (500 mg dose) in no case showed an advantage over the more slowly reached (3 h) low peak levels (2.5 µg/ml) of cefixime (200 mg dose). Cefixime was comparable to cefaclor with respect to its initial killing velocity, whereas it was generally superior with respect to maximum values for reduction of bacterial counts. Due to its long elimination half-life (2.5 h) cefixime prevented regrowth for at least twice as long as cefaclor, which has a short half-life (0.7 h). As a result of its antibacterial activity and pharmacokinetic properties cefixime can be administered less frequently than cefaclor.