Q&A: Are Antibiotics Safe?
I am not aware of any antibiotic that is not compatible with continued breastfeeding. Drugs such as ciprofloxacin and norfloxacin (and others in the same family) were not recommended for nursing moms in the past because studies on beagle puppies suggested these drugs caused abnormal joint development. However, beagles are not humans, and the puppies were given large amounts directly, not the tiny amounts that would be passed through milk. In addition, more recent studies have shown this joint damage does not occur in humans.
It is generally thought that tetracycline shouldn't be used while breastfeeding because of its effects on children younger than eight (some say 12), namely staining of developing permanent teeth. However, this risk is very small when nursing. The reason? When you are prescribed tetracycline, the pharmacist will warn you not to take it with milk because the tetracycline binds to calcium and won't be absorbed into your body. Thus if you take tetracycline while nursing, the tiny amount that gets into your milk will bind to the calcium and not get absorbed but will come out in the baby’s poop.