A randomized, double-blind, double-dummy trial was performed comparing 200 mg of cefditoren-pivoxil twice daily for 5 days versus standard cefuroxime-axetil treatment (250 mg twice daily for 10 days) of Anthonisen type I or II acute exacerbations of chronic bronchitis. The modified intention-to-treat population included 541 patients. Patients were assessed during therapy, at the end of therapy (visit 3; primary evaluation time point), and at follow-up. Clinical success was obtained in 79.9% of the 264 patients included in the cefditoren-pivoxil group and in 82.7% of the 277 patients in the cefuroxime-axetil group (treatment difference, 95% confidence interval [CI]: -2.8, -9.7 to 3.6%). Treatment clinical effects were more clearly seen in sputum signs (decreasing volume and purulence from approximately 80% to approximately 10% of the patients). At the end of treatment, exploratory analysis of the per-pathogen bacteriological response showed 72.8% (of 103 isolates) in the cefditoren-pivoxil arm versus 67.0% (of 94 isolates) in the cefuroxime-axetil group (treatment difference; 95% CI: 5.8, -7.0 to 18.6%). Globally, the per-pathogen bacteriological response correlated well with clinical success: 83.5% of 164 baseline isolates from patients with a clinical success were eradicated or presumably eradicated, in contrast to only 3% of 33 isolates from patients with a clinical failure. Clinical success in patients infected with Haemophilus influenzae, the most frequent isolate, was 84% (of 50) and 82.5% (of 40) (treatment difference; 95% CI: 1.5, -14 to 17%) in the cefditoren-pivoxil versus the cefuroxime-axetil group. Although this study does not prove that either drug is better than a placebo, cefditoren-pivoxil and the standard 10-day cefuroxime-axetil course had similar point estimates of success in acute exacerbations of chronic bronchitis.