My son had a boil positive for mrsa. They put him on eryped (erythromycin ethyl succinate)?

Ok. If the MRSA is sensitive to ertythromycin, that is fine, nasal swab is also a good idea to find out if he colonized with this resistant bacteria.
Question? It is not clear what you are asking. Assume it is whether or not this therapy is appropriate? Erythromycin may be effective against many strains of mrsa, but only the sensitivity pattern from the lab can tell you this, or clinical failure. It sounds reasonable since the other choices may not be usable in children, have a high degree of allergic reactions or are very expensive.