Therapeutic efficacy of cefadroxil and cephalexin for pneumonia in a rat test model.

The therapeutic efficacies of cefadroxil and cephalexin were compared in a Streptococcus pyogenes-induced lung infection in rats. Although MICs, rates of in vitro killing in rat serum, and antibiotic serum levels after oral administration were similar for both drugs, cefadroxil was about eight times more effective than cephalexin in reducing the number of viable streptococci at the site of infection. This excellent in vivo bactericidal activity of cefadroxil in lung tissue and bronchial secretions was reflected in the 50% protective dose (PD50) after single or multiple oral treatments. A single treatment given 24 h after infection resulted in a PD50 of 2.8 mg of cefadroxil per kg, compared with 21 mg of cephalexin per kg. When treatment was administered three times, at 24, 27, and 30 h postinfection, the PD50s of cefadroxil and cephalexin were 0.7 and 8.0 mg/kg, respectively. In infected animals, treated 24 h postinfection, the area under the lung tissue concentration versus time curve for cefadroxil was significantly greater than that of cephalexin. This difference in pharmacokinetic behavior may account, at least in part, for the superior therapeutic results obtained with cefadroxil in this experimental pulmonary infection.