Every year about five million people die of acute respiratory tract infections. Among these, pneumonia represents the most frequent cause of mortality, hospitalization and medical consultation (Bariffi, 1995).

A prospective multicenter study of 359 cases of community‐acquired pneumonia in the United States reported that 58.5% had identifiable pathogens, 32.9% had unknown etiology and 8.6% were aspiration and post‐obstructive pneumonia. The most frequent etiologic agent was Streptococcus pneumoniae(15%), followed by Hemophilus influenza (10.9%), Legionella spp(6.7%) and Chlamydia pneumoniae(6.1%) (Fang, 1990).

During the last 30 years strains of Streptococcus pneumoniae with diminished susceptibility to penicillin have emerged and spread worldwide (Austrian, 1994). Cross‐resistance to other antibiotics has also been reported in many strains of S. pneumoniae that have diminished susceptibility to penicillin and cephalosporin (Goldstein, 1996).

Interestingly, a number of studies indicated the importance of Mycoplasma pneumoniae as the main etiologic agent in ambulatory patients with pneumonia (Berntsson, 1986; Langille, 1993; Marrie, 1996). Co‐infection by more than one pathogen was also reported, and ranged from less than 10% to 38.9% (Lieberman, 1996).

The aim of microbial investigations in lower respiratory tract infections is to reduce the misuse of expensive broad‐spectrum antibiotics. The prescription of antimicrobial agents then can be performed for each specific pathogen. However, the value of routine microbial investigation in all patients with lower respiratory tract infections is uncertain (Woodhead, 1991). A survey on the management of 2,056 such infections obtained from general practitioners in France, Germany, Italy, Spain and the UK reported that microbiological examination was performed in only 7% of cases compared to 22% for chest radiography (Woodhead, 1996).

Recently, the guidelines from the Infectious Diseases Society of America for management of community‐acquired pneumonia in adults recommended that diagnostic studies include blood cultures, gram staining and cultures of expectorated sputum for patients who require hospitalization. Some immunological testings for specific microbial pathogens are also recommended, but not considered routine. The goal is a specific diagnosis allowing for more precise and often more cost effective use of antimicrobial agents. However, the utility of diagnostic studies for patients with less severity (not requiring hospitalization) is still unclear (Bartlett, 1998).

A meta‐analysis of prognosis and outcomes of 33,148 patients with community‐acquired pneumonia was performed with 127 study cohorts (Fine, 1996). It reported the overall mortality was 13.7% ranging from 5.1% for hospitalized and ambulatory patients to 36.5% for intensive care unit patients. Mortality was strongly associated with pneumonia etiology. By bacterial agents, mortality was lowest for patients with Chlamydia psittaci(0%), Coxiella burnetii(0.5%), and Mycoplasma pneumoniae(1.4%) and highest for patients with Pseudomonas aeruginosa(61.1%), Klebseilla species(35.7%), Escherichia coli(35.5%) and Staphylococcus aureus(31.8%). Among patients with pneumonia due to S. pneumoniae, the most prevalent bacterial pathogen had an over all mortality of 12.3%, ranging from 6.4% in patients treated in an ambulatory and hospital setting to greater than 37% in patients treated in an intensive care unit (Fine, 1996).

Antimicrobial treatment in lower respiratory tract infections has to be effective, partly because of the need to reduce the cost and also the problem of increasing resistance to the commonly used antibiotics (Legnani, 1997). It has also been suggested that the start of therapy should not be delayed for longer than six hours for diagnostic studies (Brown, 1998). The importance of early antimicrobial treatment was supported by a study in elderly patients with pneumonia which showed that 30 day mortality was lower after administration of antibiotics within 8 hours of arrival at hospital than after delayed treatment (Meehan, 1997).

Compliance is also important, particularly in ambulatory patients. A study related to medical compliance for the out‐patient management of infectious diseases indicated that there was an inverse relationship between frequency of dose and compliance. A short term regimen with administration once a day was found to have the highest compliance rate, 80% compared to 69% and 38% for administration twice a day and three times a day respectively (Sclar, 1994).

Amoxycillin, an oral antibiotic, constitutes extended spectrum penicillin and is active against many aerobic gram‐negative bacilli encountered in patients with pneumonia. By combining the beta‐lactamase inhibitor, clavulanic acid with amoxycillin, the in vitro spectrum of penicillin is expanded to include beta‐lactamase producing organisms which would otherwise be resistant to this drug (Mandell, 1994). Amoxycillin has been accepted to be one of the first choice antibiotics in patients with community‐acquired lower respiratory tract infections. Amoxycillin‐clavulanic acid is recommended particularly in the high prevalence area of beta‐lactamase producing organisms, and also when an etiologic agent is not identified (Huchon, 1998; Bartlett, 1998).

Azithromycin is a new macrolide antibiotic structurally modified from erythromycin with an expanded spectrum of activity and improved tissue pharmacokinetic characteristics relative to erythromycin. The drug is noted for its activity against some gram‐negative organisms associated with respiratory tract infections, particularly Haemophilus influenzae. Azithromycin has similar properties to other macrolides against Streptococcus pneumoniae and Moraxella catarrhalis, and is active against atypical pathogens such as Legionella pneumophilae, Chlamydia pneumoniae and Mycoplasma pneumoniae (Dunn, 1996).