Block protein synthesis but reversibly hence bacteriostatic rather than bacteriocidal cf aminoglycosides. Effective against a range of Gram-positive cocci so used as an alternative to penicillin in allergic patients. Variable resistance seen; sometimes effective against penicillin-resistant staphylococci including some MRSA, but poor activity against Haemophilus. Variable resistance seen in streptococcus and pneumococcus. They are also effective against a range of intracellular pathogens, particularly Chlamydia, Bordetella pertussis, Mycoplasma pneumoniae, and Legionella pneumophila. Also active against Corynebacterium diphtheriae, Treponema pallidum and Campylobacter species.
All have gastrointestinal side effects. Newer macrolides tend to achieve better plasma levels and have less side effects.
They have lots of drug interactions!