Dear Colleagues:

I wish to issue a word of clarification concerning the use of tetracyclines and
more importantly, doxycycline in breastfeeding mothers.

Whereas it has been the rule of thumb that calcium and aluminum containing
products (antacids, milk) significantly reduce the bioavailability of the older
tetracyclines,   this is not necessarily the case for the newer more
bioavailable tetracyclines such as doxycycline.

While, coadministered calcium and aluminum salts reduce the bioavailability of
doxycycline to some degree, the actual plasma levels drop only from about 1.4
to 0.9 mg/L. So while we caution people not to take doxycycline with antacids,
it is now sometimes recommended that doxycycline can be administered with milk
to reduce its GI distress.  True,  milk and probably antacids reduce or slow
the bioavailability of doxycycline,  they do not "eliminate" its absorption
totally.  So lets not misconstrue some reduction in total bioavailability with
"complete" that is often misquoted.

In a breastfeeding mother,  the concentration secreted in breastmilk is small,
about 0.77 mg/L,  so the risk is not paramount.  But long term exposure, such
as 1-6 months when the mom is taking it for acne, etc,  may produce unwanted
sequalae in breastfed infants, such as stained teeth or premature closure of
the epiphyseal growth plate and shortened stature.

So we still need to be cautious of the newer tetracyclines, and with older
misconceptions.

Regards
Tom Hale, Ph.D.