Dirithromycin (Dynabac) is a macrolide glycopeptide antibiotic used to treat different types of bacterial infections, such as bronchitis, pneumonia, tonsillitis, skin infections. Dirithromycin is a semi-synthetic derivative of erythromycin - the hemi-aminal resulting from the condensation of (9S)-erythromycyclamine with 2-(2-methoxyethoxy) acetaldehyde. Being unstable under both acidic and alkaline conditions, dirithromycin functions as a more lipid-soluble prodrug for (9S)-erythromycyclamine. Erythromycylamine exerts its activity by binding to the 50S ribosomal subunits of susceptible mircoorganisms resulting in inhibition of protein synthesis. Dirithromycin has been shown to be active against most strains of the following microorganisms both in vitro and in clinical infections: Staphylococcus aureus (methicillin-susceptible strains only), Streptococcus pneumoniae, Streptococcus pyogenes, Haemophilus influenzae, Legionella pneumophila, Moraxella catarrhalis, and Mycoplasma pneumoniae. Dirithromycin showed better activity in vitro against Campylobacter jejuni and Borrelia burgdorferi than erythromycin or clarithromycin but in general demonstrated less activity than erythromycin, clarithromycin, or azithromycin against a majority of microorganisms. The pharmacokinetic profile of dirithromycin has advantages over other microlides of once-daily dosing and high and prolonged tissue concentrations but adverse effect profiles similar to those of the other macrolides, with reported problems most often related to the gastrointestinal tract.