9:37 pm - 08/30/2013

Keflex, the pill & chance of pregnancy?

Hello Superstars!

Some background - taking Levlen ED daily, once a week i may take it a couple or hours late, rarely, if ever, miss a pill.


On the 9th of august i had all 4 wisdom teeth out and was prescribed Keflex for 7 days to ward off any infections. I finished taking keflex on the 16th and 7 Days after that, the 23rd august (a week ago today), My partner and I had sex and he did not pull out. I usually stack my pill for 2 to 3 months and then have a break. I think my last period was the 2nd last or last week of july. Im usually very careful when it comes to antibiotics, but this time i just didnt give it a thought and now its playing on my mind.

what could be my risk? Is there a reasonable chance i could fall pregnant and if so, when should i test and should i try for a breakthrough bleed before then?

elialshadowpine 30th-Aug-2013 01:24 pm (UTC)
I believe it's actually specific kinds of antibiotics that cause problems with birth control. I'm not finding any concrete information on a Google search (most of the results are coming up of people giving the standard "all antibiotics can do this", which isn't true). Maybe someone else will have better luck with google than me.

However, I would note that pregnancy rarely happens on the first try. Most people who are trying to get pregnant take awhile before they actually do. Chances are possible, I'd say, but pretty low.

Standard time that you can get a reliable test is 19 days after the sex in question.
archangelbeth 30th-Aug-2013 07:37 pm (UTC)
The trick is to add site:gov to your search. This screens out the cesspool of misinformation that is, for instance, Yahoo Answers. *shudder*
archangelbeth 30th-Aug-2013 07:37 pm (UTC)
Last time I went digging around... Basically, except for Rifampin and its "family," there are no antibiotics that definitely affect the level of pill-hormones in the bloodstream.

There are a few, nearly anecdotal, instances of people ovulating when on antibiotics and the pill -- but the thing is... well, http://www.ncbi.nlm.nih.gov/pubmed/12436822 says: "Considering that both drug classes are prescribed frequently to women of childbearing potential, one would expect a much higher rate of oral contraceptive failure in this group of patients if a true drug:drug interaction existed. On the other hand, if the interaction does exist but is a relatively rare event, occurring in, say, 1 in 5000 women, clinical studies such as those described in this article would not detect the interaction."

So if antibiotics could compromise protection, it would be in rates undetectable from the normal typical-use failure rate. However, there is a chance some people might be susceptible to having their protection compromised, so using backup is advised because such people cannot be predicted in advance.

So. Your chance of pregnancy is Really Really Low, statistically. Testing 19 days after the sex in question is when you can generally trust a negative result. I wouldn't try for a withdrawal bleed before then. Just do a test and don't stress.

Good luck!
tsemed_chemed 31st-Aug-2013 09:06 pm (UTC)
My Lippincott's Nursing Drug Guide does mention interactions between birth control and antibiotics when there is some minor risk of pregnancy, but for Keflex it doesn't say anything, so hopefully you're in the clear.
tinykristen 31st-Aug-2013 11:11 pm (UTC)
did a little research.. Levlen is levonorgestrel/ethinyl estradiol

Check out this info from eMPR (electronic Monthly Prescribing Reference. We receference it a lot in the office to check drug interactions..

http://www.empr.com/drug-interactions-checker/section/2462/#


So, although it isn't a "class 1" interaction, it's still a high classed interaction. Whenever we put a patient on antibiotics who is also on birth control, we recommend a backup protection for the rest of their cycle. So if you did have unprotected sex during the cycle when you were on antibiotics, and you don't get your withdraw bleed (period) this month, it wouldn't hurt to take a pregnancy test. Good luck!!
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