Antibiotic-Associated Diarrhea (AAD) is a common complication of antibiotic use. The frequency of AAD can be high (26 - 60%) or moderate (13-29%) during hospital outbreaks and is relatively infrequent in outpatients. The risk factors for AAD include broad-spectrum antibiotics, host factors (age, health status, and gender), hospitalization period and exposure to nosocomial pathogens. AAD occurs 2-8 weeks after exposure to antibiotics as a result of disrupting normal intestinal microflora. One of the roles of normal intestinal microflora is to act as a protective barrier that resists the colonization of intestinal pathogens. These patients are susceptible to infection by opportunistic pathogens without this protective barrier. Probiotic therapy is suited to AAD and Clostridium difficile disease. Probiotics assist in reestablishing the disrupted intestinal microflora, enhancing immune responses and clearing pathogens and their toxins from the host. Studies using probiotics have been reported for the past twenty-eight years (1977~2005), but the studies have been variable in trial designs and types of probiotics, had differing doses and durations of treatment, and thus have yielded controversial results. The investigators will conduct a multi-center, randomized, placebo-controlled, double-blind trial to assess the efficacy of the probiotic Lactobacilli (Lacidofil cap®) for the prevention of AAD in adults.

Inclusion Criteria:

• Male or female over 18
• Patients with respiratory tract infection who are receiving an oral or injection antibiotics.
• Signed informed consent form prior to inclusion in the study.
• Patients who begin receiving antibiotics within 48 hours before enrollment in this study.

Exclusion Criteria:

• Diagnosed Clostridium difficile colitis within the last 3 months
• Patients with tube feeding, ileostomy or colostomy
• Patients with basal diarrheal disease; acute enteritis, chronic diarrhea such as inflammatory bowel disease (IBD) etc, radiation enteritis, ischemic colitis and diarrhea caused by carcinoids etc.
• Patients receiving other probiotics during the last 15 days
• Patients treated with immunosuppressant drugs or immune deficiency patients
• Patients with radiotherapy and chemotherapy treatment for cancer.
• Patients treated with antidiarrheal, antispasmodic or motility agents for other diseases.
• Pregnant/Lactating women
• Patients with gastrointestinal (GI) surgery during the last 3 months.
• A history of hypersensitivity to cephalosporins, penicillin or clavulanic acid.
• Patients with verified diabetic autonomic neuropathy.
• Patients with organ transplants.
• Patients with underlying conditions or diseases which, in the opinion of the investigator, are unsuitable for inclusion.

Patients with respiratory tract infection who begin receiving antibiotic therapy (both hospitalized patients and out-patients)