Hi All,
From T. Hale 3rd Edition:

ZITHROMAX
Generic = AZITHROMYCIN
Antibiotic. Belongs to the Erythromycin family.  Extremely long half-life.
 Azithromycin is concentrated for long periods in phagocytes which are known
to be present in human milk.  No data exists concerning the transfer into
breast milk.  As there are no pediatric indications for this medication,
caution should be observed in using this medication in nursing mothers.  AHL
= 68 hrs.  PB = 7-51%


Hope this helps!
Jay