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Reporters Perpetuate Some Imprecision – The Tennessean and Antibiotics vs. Oral Contraceptives

May 28, 2009

Note: The piece in question apparently originated with Liz Szabo at USA Today rather than the Tennessean itself.
Today’s Tennessean (Nashville newspaper) has an article, “Doctors Perpetuate Some Myths,” which treats us to such ground-breaking knowledge as the fact that bacteria and viruses make you sick, not going out in the cold, and you won’t necessarily drown if you swim less than an hour after eating. Shocking, I know. And it never quite gets around to describing how doctors might be actively perpetuating any of these myths, rather than their just existing as part of the collective, erroneous consciousness. An insightful piece on evidence-based medicine it’s not.

Aside from these generalities, the article contains the following statement:

Birth control pills don’t work as well if you’re on antibiotics. – A review by the American Academy of Family Physicians found common antibiotics have no effect on the pill.

It bothers me enough when reporters refer to papers or studies and don’t provide any citations or links, but I understand it. The problem here is that the above statement is not exactly true, for a number of reasons:
1) At least one antibiotic drug, rifampin, *is* thought to potentially interfere with oral contraceptive efficacy (it is commonly used for tuberculosis, which many women may not be affected by, but it’s still worth knowing);
2) The AAFP didn’t actually say that there is absolutely “no effect” (and they do note the rifampin issue);
3) I’m bugged about the idea that a “review” “found” anything. This is more nitpicky for the librarians, clinicians, and such, who all know that reviews just examine and characterize the existing literature – they are not new investigations with their own findings.

Now, there is definitely a persistent idea that antibiotics interfere with oral contraceptives, and a fair bit of literature that fails to demonstrate any interaction or reduced levels of the drug in the body with concomitant antibiotic administration. There are also critiques of the existing literature that may suggest an association between antibiotic use and contraceptive failure, describing limitations of those study designs and sizes. One problem here is that, as one author notes – “There are also no prospective, randomized clinical trials of OC efficacy and antibiotic use” – but it seems unlikely that a large, prospective study would be done to randomize women to oral contraceptives with or without an antibiotic to see if those with get disproportionately knocked up – the consequences are too serious.

Some authors hedge by saying that if there is an effect, it may be unusual enough to be indistinguishable from the normal OC failure rate with typical use or that it may happen in some subset of women who cannot be identified in advance, so caution may be warranted. Others respond by calling out this wishy-washiness, with statements such as “This nonevidence-based opinion increases anxiety, liability, and expense without proven benefit.”

Getting back to point #2 – the AAFP never actually says definitively that “common antibiotics have no effect on the pill.” In their 1999 Update on Oral Contraceptive Pills, they write:

The possibility that some antibiotics decrease the effectiveness of oral contraceptive pills has been widely reported. Unfortunately, the literature supporting an oral contraceptive pill­/antibiotic interaction consists of anecdotal reports or descriptive studies that included no controls or gave questionable historical control rates.

Rifampin (Rifadin) is the only antibiotic that has been shown to decrease estrogen and progestin levels by hepatic enzyme induction and to significantly reduce the efficacy of oral contraceptive pills. Retrospective case studies indicate a weak association between ampicillin, amoxicillin, metronidazole (Flagyl) and tetracycline and ineffectiveness of oral contraceptive pills. Only isolated case reports have linked oral contraceptive pill failure to griseofulvin (Gris-Peg), clindamycin (Cleocin), cephalexin (Keflex), dapsone, isoniazid (INH), trimethoprim (both alone [Proloprim] and combined with sulfamethoxazole [Bactrim, Septra]) and erythromycin.

More importantly, antibiotic-related diarrhea may be associated with decreased absorption of oral contraceptive pills and a diminished therapeutic effect.

It is important to realize that the inherent failure rate of oral contraceptive pills is much higher than the small, theoretically increased failure rate in women who are taking antibiotics. Nevertheless, it may be prudent for women to use a back-up contraceptive method during antibiotic therapy and for seven days after completing the antibiotic course or having the last episode of vomiting and diarrhea.

Now, while acknowledging the lack of sufficient evidence demonstrating an interaction, does the above sound at all like the AAFP “found common antibiotics have no effect on the pill?”

In a 2000 review, Clinically Significant Drug Interactions, the organization revisits the topic, notes the controversy, the failure of definitive studies to demonstrate an effect of antibiotics on the pill, the difficulty in distinguishing any real failures due to antibiotics from the normal failure rate, and still concludes: “Although insufficient evidence is available to make a firm conclusion, it appears possible that oral contraception may fail while patients are taking an antibiotic. Thus, patients should be encouraged to consider using an alternative method of contraception for the duration of the cycle.”

Again, no strong statement that “common antibiotics have no effect on the pill.” Yes, it appears that the evidence is not really there – at present – to demonstrate any effect. But there are a whole bunch of factors, mentioned above, that cause authors to decline to come out and say “nope, there is definitely no effect.” It feels irresponsible to me to pretend otherwise in a one-sentence oversimplification for newsy purposes.

Some references, if you’re interested, mostly reviews (follow the citations in those if you’re even more interested):

  • Archer JS, Archer DF. Oral contraceptive efficacy and antibiotic interaction: a myth debunked. J Am Acad Dermatol. 2002 Jun;46(6):917-23. Review. PMID: 12063491
  • Dickinson BD, Altman RD, Nielsen NH, Sterling ML; Council on Scientific Affairs, American Medical Association. Drug interactions between oral contraceptives and antibiotics. Obstet Gynecol. 2001 Nov;98(5 Pt 1):853-60. Review. PMID: 11704183
  • Lindsey JL, Hugin M. Drug interactions between oral contraceptives and antibiotics. Obstet Gynecol. 2002 May;99(5 Pt 1):841-2; author reply 842. PMID: 11978298 [letter]
  • Weaver K, Glasier A. Interaction between broad-spectrum antibiotics and the combined oral contraceptive pill. A literature review. Contraception. 1999 Feb;59(2):71-8. Review. PMID: 10361620
4 Comments leave one →
  1. May 28, 2009 10:16 am

    It’s the Tennessean. Their reporting is lousy, and their headlines are notoriously wrong. Recently they had a headline about preparing for medical procedures and the article was inter alia about getting bikini waxes.

  2. May 28, 2009 10:24 am

    I know, and it really bothers me when their lack of accuracy/quality control may have real and serious consequences. Blech.

  3. May 28, 2009 4:03 pm

    I had to go on amoxicilin last December, and my pharmacist warned me that it could weaken the Pill and that I should use a backup form of birth control during that week (I would have anyway, and this was right before exams so it’s not like I was having sex with anyone right then!). You better believe I trust my pharmacist far more than I trust the Tennessean.

  4. May 30, 2009 6:11 pm

    What a smart breakdown. Please please cross-post this one. I may even forgive Hawaii!

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