To compare the efficacy of a 5-day course of clarithromycin extended-release tablets (2 x 500 mg QD) with that of a 7-day course of clarithromycin immediate-release tablets (1 x 500 mg BID) in the treatment of acute bacterial exacerbation of chronic bronchitis.

Inclusion Criteria:

• Ambulatory subject who does not require intravenous antibiotic therapy.
• Subject who has a medical history of chronic bronchitis.
• A history of regular medication use (>=3 consecutive months within the past 2 years) to treat pulmonary disease.
• Subject must have evidence of pulmonary function test abnormalities.
• The onset of signs and symptoms of the current exacerbation must occur within 14 days before Evaluation 1.

Exclusion Criteria:

• Medical history of hypersensitivity, allergic or adverse reactions to clarithromycin, erythromycin, or any of the macrolide antibiotics.
• A female who is pregnant or is lactating.
• Subject who has suspected or known (positive chest radiograph) pneumonia.
• Subject who has evidence of significant bronchiectasis (by CT) or atelectasis, active tuberculosis or other mycobacterial infection, bullous emphysema, pulmonary embolism, lung abscess, tumor (primary or metastatic) involving the lung, pleural effusion, or cystic fibrosis that could confound the assessment of signs and symptoms of ABECB.
• Subject who requires parenteral antibiotic therapy.
• Subject who requires hospitalization for treatment of current episode of ABECB.
• Subject who has any other infection or condition, which necessitates use of a concomitant systemic antibiotic.
• Subject who has any underlying condition/disease, which would be likely to interfere with the completion of the course or absorption of study drug therapy or follow-up.
• Subject who has a severe or complicated lower respiratory tract infection or a severely compromised respiratory status (i.e., oxygen dependent, requiring hospitalization).
• Known significant renal or hepatic impairment.