The AAP considers tetracycline compatible with breastfeeding.  Very
little gets into the milk.  Tetracycline causes staining of the teeth
because it binds to calcium which is incorporated into teeth and bones
in the growing child.  However, this very quality makes it compatible
with breastfeeding.  The very little that gets into the milk will bind
to calcium in the milk and not be absorbed by the baby.  Therapeutics
teaching has always been not to take tetracycline with milk.

Periodontal problems can be treated with other antibiotics, by the way.

Jack Newman, MD, FRCPC