I'm glad your friend is willing to educate herself on what's known --
and not known -- about these drugs, and the choices she faces. And
glad, too, that you're willing to assist her in this.
As I'm sure you know -- and can see by the disclaimer at the page
bottom -- Google Answers is not a source of medical advice, and is
certainly no substitute for seeking input from a medical professional.
However, I can certainly provide available information on the
medicines you mentioned, with a particular emphasis on risks during
Taking any drugs during pregnancy is always a difficult choice,
because -- in general -- very little is known about actual or
potential effects of drugs on the developing fetus.
Much of the information available about the safety of drugs comes from
animal studies, which provide useful -- but limited -- insights into
possible effects in humans.
Observational studies may also be carried out on pregnant women who do
decide to take medicines during pregnancy, but these types of studies
generally involve fairly small numbers of women and, again, can only
provide limited insight into the relative safety or dangers of
Even the classifications into category B can sometimes mean something
along the lines of "we simply don't know enough about this drug to
move it into category A".
Your friend is basically faced with a choice between the following:
--use a single dose of Zithromax in the first trimester
--use erythromycin over the course of a few weeks during the first trimester
--delay treatment with either drug until later in the pregnancy
--take no drugs at all
--use a different drug for treating Chlamydia
The drugs themselves pose risks, but so does delaying treatment or
leaving the disease untreated.
Hopefully, having a better background on the drugs in question will
help your friend in coming to her decision.
--Azithromycin (Zithromax) has not raised any serious red flags in
terms of affects on a developing fetus. At the same time, the drug
has not been the object of intensive study on this front, so any
conclusions that can be drawn are necessarily tentative.
--In animal studies (rats and mice), even very high doses of the drug
did not result in adverse effect on the animal fetus, even at doses
where the drug began to have toxic effects on the mother.
--In humans, there is very little transfer of azithromycin across the
placenta, so that exposure of the fetus is presumed to be low.
--There is very little literature on the use of azithromycin during
the first trimester. One study looked at such use in eleven women,
with no apparent effects on the fetus (the eleven women had ten normal
and healthy births, and the 11th women had an elective abortion).
--There is at least one case report of a women who miscarried three
weeks after using azithromycin early in her pregnancy. However, the
women had a history of prior miscarriages, and was ill...it is not
known whether the use of the drug contributed at all to the
miscarriage that was reported.
--The use of azithromycin to treat Chlamydia was explicitly studied in
42 women, who used the drug during their 2nd or 3rd trimesters. No
unusual level of adverse effects on the fetus/infants were reported.
--In the most recent (2006) study, 277 pregnant women treated for
Chlamydia were studied. Treatment with azithromycin (or amoxicillin)
was more effective than erithromycin, and there was no apparent
difference between drugs in the number of neonatal complications
--One study suggests that more women have a mild intolerance to
azithromycin than to amoxicillin, though the difference was not great.
--In general, azithromycin is not yet considered to be well-studied in
pregnant women. However, at least some medical organizations are
comfortable recommending azithromycin for use during pregnancy as an
apparently 'safe and effective' treatment, and the use of azithromycin
appears to be increasing.
--No serious red flags have been raised regarding the use of
erythromycin during pregnancy.
--In animal studies, erythromycin comes up pretty clean...that is, no
effects on mothers or infants.
--However, the literature on human beings is regarded as incomplete
and, hence, not conclusive as to safety.
--Recent studies suggest that erythromycin is not as effective as
either azithromycin or amoxicillin for the treatment of Chlamydia
--Erythromycin is generally (in the US) recommended as a 7-day course
of multiple daily 500 mg doses, or a 14 day course of 250 mg doses,
for the treatment of Chlamydia.
--Again, no serious red flags.
--High dose animal studies did not reveal any effects on newborns
--Dosage is similar to that of erythromycin
--Amoxicillin appears to be more effective than erythromycin in the
treatment of Chlamydia, and equally as effective as azithromycin
--There is little direct human study on safety during pregnancy,
though observations on pregnancy and birth outcomes among women using
amoxicillin have not raised any alarms as far as safety.
--Amoxicillin is chemically similar to penicillin, which is generally
regarded as safe during pregnancy.
--Amoxicillin is a category B drug.
I must say, that, were it a friend of mine, I would certainly
recommend either amoxicillin or azithromycin over erythromycin, since
the latter seems to be the least effective of the three, and there is
no notable difference in safety concerns. And while I share your
"common sense" notion that one dose is better than 25 or 50, this
certainly seems something to discuss in more detail with a doctor.
Here is a list of some of the key resources used in compiling this
information, along with a few annotated comments of my own:
[The three links that follow are from a well-regarded site for drug information]
Diagnosis and Treatment of Chlamydia in Pregnancy
[a little bit dated, but worth reading just the same]
Sex Transm Dis. 2006 Feb;33(2):106-10.
An observational cohort study of Chlamydia trachomatis treatment in pregnancy.
Rahangdale L, Guerry S, Bauer HM, Packel L, Rhew M, Baxter R, Chow J, Bolan G.
[NOTE that Dr. Rahangdale's email address at the University of
California is given as RahangdaleL@obgyn.ucsf.edu As this is a
very recent study comparing the three drugs in the treatment of a form
of Chlamydia, you may want to have your friend's doctor contact the
study's author for guidance]
Am J Obstet Gynecol. 2001 Jun;184(7):1352-4; discussion 1354-6.
Related Articles, Links
A randomized controlled trial comparing amoxicillin and azithromycin
for the treatment of Chlamydia trachomatis in pregnancy.
Jacobson GF, Autry AM, Kirby RS, Liverman EM, Motley RU.
Department of Obstetrics and Gynecology at University of Wisconsin
Medical School-Milwaukee Clinical Campus, Wisconsin 53233, USA.
[Again, a bit dated, but worth noting]
Please let me know if there's anything else I can do for you on this,
and all the best to your friend her baby-to-be.
search strategy -- Numerous Google searches on the names of the
individual drugs along with the terms [ pregnant OR pregnancy ] [