AZITHROMYCIN - A REVIEW OF ITS PHARMACOLOGICAL PROPERTIES AND USE AS 3-DAY THERAPY IN RESPIRATORY-TRACT INFECTIONS

The azalide antibacterial agent azithromycin is a semisynthetic acid-s table erythromycin derivative with art expanded spectrum of activity a nd improved tissue pharmacokinetic characteristics relative to erythro mycin. The drug is noted for its activity against some Gram-negative o rganisms associated with respiratory tract infections, particularly Ha emophilus influenzae. Azithromycin has similar activity to other macro lides against Streptococcus pneumoniae and Moraxella catarrhalis, and is active against atypical pathogens such as Legionella pneumophila, C hlamydia pneumoniae and Mycoplasma pneumoniae. Once-daily administrati on of azithromycin is made possible by the ling elimination half-life of the drug from tissue. Azithromycin is rapidly and highly concentrat ed in a number of cell types after absorption, including leucocytes, m onocytes and macrophages. It undergoes extensive distribution into tis sue, form where it is subsequently eliminated slowly. A 3-day oral reg imen of once-daily azithromycin has been shown to be as effective as 5 - to 10-day courses of other more frequently administered antibacteria l agents [such as erythromycin, amoxicillin-clavulanic acid and phenox y-methylpenicillin (penicillin V)] in patients with acute exacerbation s of chronic bronchitis, pneumonia, sinusitis, pharyngitis, tonsilliti s and otitis media. Adverse effects of azithromycin are mainly gastroi ntestinal in nature and occur less frequently than with erythromycin. Azithromycin is likely to prove most useful as a 3-day regimen in the empirical management of respiratory tract infections in the community. Its ease of administration and 3-day duration of therapy, together wi th its good gastrointestinal tolerability, should optimise patient com pliance (the highest level of which is achieved with once-daily regime nts). Azithromycin is also likely to be useful in the hospital setting , particularly for outpatients and for those unable to tolerate erythr omycin.