OBJECTIVE: To review the pharmacology, microbiology, chemistry, pharmacokinetics, efficacy, safety, tolerability, dosage, administration, and economic issues of intravenous azithromycin. DATA SOURCES: A MEDLINE search from 1978 to May 1998 of the English-language literature and an extensive review of journals and meeting abstracts was conducted. Due to the lack of published literature concerning the efficacy, safety, and pharmacokinetics of the intravenous formulation of azithromycin, the manufacturer was also contacted and requested to supply information concerning intravenous azithromycin. DATA EXTRACTION: In vitro and preclinical studies were included, as well as data from Phase II and III clinical trials. Efficacy, pharmacokinetic, safety, and tolerability data were also supplemented with information from the manufacturer, due to the lack of published reports. DATA SYNTHESIS: Azithromycin, an azalide subclass of the macrolide antibiotics, is now available as an intravenous formulation. The intravenous form is approved for the treatment of community-acquired pneumonia caused by Chlamydia pneumoniae, Haemophilus influenzae, Legionella pneumophila, Moraxella catarrhalis, Mycoplasma pneumoniae, Staphylococcus aureus (methicillin-sensitive), and Streptococcus pneumoniae, and for the treatment of pelvic inflammatory disease caused by Chlamydia trachomatis, Neisseria gonorrhoeae, and Mycoplasma hominis in situations in which intravenous therapy is required. Its spectrum of activity, unique pharmacokinetics, and high and sustained tissue penetration allow for once-daily dosing with monotherapy in many cases. Clinical and bacteriologic response rates as well as the adverse event profile have been similar to or better than comparative agents. CONCLUSIONS: Azithromycin offers advantages over other agents due to its unique pharmacokinetics, high and sustained tissue penetration, and spectrum of activity. This allows for monotherapy and once-daily intravenous dosing for mild-to-moderate community-acquired pneumonia or pelvic inflammatory disease in many instances. Future research should focus on total duration of antibiotic therapy and the need, or lack thereof, for extensive oral antibiotic follow-up.