A macrolide is class of antibiotics discovered in Streptomyces. It is characterized by molecules made up of large-ring lactones. An example is erythromycin. A macrolide works by inhibiting protein synthesis.
Macrolides are considered bacteriostatic at therapeutic concentrations, but they can be slowly bactericidal, especially against streptococcal bacteria; their bactericidal action is described as time-dependent. The antimicrobial action of some macrolides is enhanced by a high pH and suppressed by low pH, making them less effective in abscesses, necrotic tissue, or acidic urine.
Macrolides are used in the treatment of infections such as respiratory tract and soft tissue infections. The antimicrobial spectrum of macrolides is slightly wider than that of penicillin, and therefore macrolides are a common substitute for patients with a penicillin allergy.