To :Mary Kay Re : Levofloxacin(Levaquin) Levofloxacin is a the S(-) enantiomer of ofloxacin so its breastmilk kinetics would probably be similar to ofloxacin (0.05-2.41 mg/Liter..see '97 edition of my book). In general the quinolones are not preferred antibiotics in breastfeeding mothers for a number of reasons including pseudomembranous colitis in one reported infant. I have two suggestions, norfloxacin(another quinolone) apparently does not enter milk in significant levels and could be used instead. Secondly, the fluoroquinolones chelate strongly with magnesium, and calcium, significantly reducing their oral bioavailability. I doubt that signficant levels would be absorbed while dissolved in milk. Lastly, using quinolone antibiotics in respiratory tract infections is really rare and I'm wondering why choose this drug? Is this supported by culture, or can some other antibiotic be used instead ( like a cephalosporin). Regards Tom Hale, Ph.D.