You can tell which doctor I would prefer to believe.

July 16, 2009 7:18 AM

Which doctor should I believe?

I take doxycycline for acne and Apri for birth control. When I went to Planned Parenthood a few months ago for information on methods other than the pill, I asked about interactions between the two and was completely reassured by the doctor there that I had nothing to worry about and the pill would work fine while i was taking the antibiotics (this was one of the main reasons I decided not to get an IUD). I went back about two weeks ago to get a new prescription, and the (different) doctor noted the medications I was taking and made no comment. But yesterday I went to the dermatologist to get a new antibiotics prescription and she warned me that I should be extra careful with my birth control and that the antibiotics could lessen the pill's effects. So now I'm mildly freaking out. We use condoms too, but after a little bit of initial entry. Who can I believe about this? Who could I ask to get a definitive answer? Is there any definitive answer?

posted by sarahj to health & fitness (8 comments total)

From wikipedia:

"Previously, it was believed that doxycycline impairs the effectiveness of many types of hormonal contraception due to CYP450 induction. Recent research has shown no significant loss of effectiveness in oral contraceptives while using most tetracycline antibiotic (including doxycycline), although many physicians still recommend the use of barrier contraception for people taking the drug to prevent unwanted pregnancy."
posted by splice at 7:28 AM on July 16

I see this at mayoclinic.com, where it states that rifampin is the only antibiotic that has been clearly shown to have an effect on the pill:

Hypothetically speaking, other antibiotics, particularly penicillin and tetracycline derivatives, could impair the effectiveness of birth control pills in a small percentage of women. Researchers can't rule out this possibility, but no large studies have proved such an effect.

It goes on to say that if you're concerned, you should use a barrier method, which it sounds like you are already doing. (IANAD)
posted by cabingirl at 7:29 AM on July 16

There isn't a definitive answer. The current consensus seems to be that amoxicillin can indeed decrease effectivity in certain women, but other antibiotics haven't really been tested. Some people think there's no problem, but most doctors would recommend erring on the safe side. I've breezed through these warnings before and have been fine (which was stupid in retrospect), but when I started spotting while taking penicillin a couple of months ago, I hopped right on the condom train.

It sounds like you'll be fine, though-- if the doxycycline has any effect, it'd be to lessen, not negate, the pill's effectivity. So as long as you're careful about taking the pill every day at the same time, the worst you're probably looking at about the same risk you'd be at if you missed a couple of pills.
posted by oinopaponton at 7:31 AM on July 16

I would probably ask a pharmacist here. In my experience, pharmacists will look this sort of stuff up for you. This is what DRUGDEX says about the interaction between contraceptive combinations and doxycycline:

1) Interaction Effect: decreased contraceptive effectiveness
2) Summary: Tetracyclines may alter intestinal flora which, in turn, may alter the enterohepatic circulation of combination contraceptives. Concomitant use has been associated with unintended pregnancies and menstrual changes (Prod Info Ortho Evra(TM), 2001d; Szoka & Edgren, 1988; True, 1982a; Back et al, 1981a). During a four-year period documenting 163 cases of oral contraceptive failure in reliable pill takers, 37 cases of pill failures (23%) were attributed to the concomitant use of antibiotics. Tetracyclines, including doxycycline, were featured in six of these 37 cases (Sparrow, 1987).
3) Severity: moderate
4) Onset: delayed
5) Substantiation: probable
6) Clinical Management: During concurrent use of doxycycline and combination contraceptives, an additional form of birth control should be used.
7) Probable Mechanism: decreased enterohepatic circulation
8) Literature Reports
a) The effect of doxycycline on serum levels of estradiol and norethindrone was studied in 24 women taking oral contraceptives (Neely et al, 1991). The subjects had been taking an oral contraceptive containing 1 mg norethindrone and 35 mcg ethinyl estradiol for at least two months prior to the study. Administration of doxycycline 100 mg daily for seven days starting on day 14 of the 28-day cycle had no significant effect on the average serum levels of estradiol and norethindrone, however, there was substantial variability. Progesterone levels indicated that ovulation had not occurred in any of these subjects. Although no significant effect was observed in this study, antibiotics may have an effect in patients with unusually low oral contraceptive hormone levels.
b) The interaction between oral contraceptives and tetracycline has been suggested to be due to an alteration of the gut flora (True, 1982). The normal gut flora is thought to be responsible for the hydrolysis of the glucuronide moiety (estrogen metabolite found in the bile) to free drug. When the gut flora is altered, enterohepatic recirculation is reduced and the metabolite is simply excreted. This causes a decrease in body levels of the estrogen and reduced effectiveness.

posted by grouse at 7:32 AM on July 16

I looked up some of the supporting links from the Wikipedia blurb that splice quoted, from an article called "Oral contraceptive efficacy and antibiotic interaction: A myth debunked" in the Journal of the American Academy of Dermatology. The authors really did not seem to think much of the Sparrow study, and among other things note that the study participants might have been lying. Wow.

It should also be noted that the women described in the study by Sparrow were seeking a therapeutic abortion and could have used their antibiotic history as a justification for this procedure.

posted by grouse at 7:41 AM on July 16

I'll second grouse to say you should ask a pharmacist. I don't know about the USA, but in the UK a licensed pharmacist should know a great deal about drugs, covering their mechanism, stability and interactions. By contrast, a doctor is far better at diagnoses and choosing treatments but probably has less detailed knowledge about how the drugs work and how they'd be expected to interact.

(My experience talking to medical doctors sometimes makes me scared about how little they tend to understand about what various drugs and pathogens are actually doing inside the body. A great deal of the training seems to be along the lines "see these symptoms > give this treatment" without much discussion of the whys and wherefores. Still, it does seem to work for them so it's probably just me being irrational.)
posted by metaBugs at 8:53 AM on July 16

Seconding the pharmacist.

This is an area where pharmacists are trained and in the US are really underutilized for it.

I've called our pharmacists multiple times about OTC meds we had for the baby, and always her answer was the same as our doctor's --- and was often faster to get.
posted by zizzle at 11:02 AM on July 16

Definitely consult a pharmacist. They know far more about drugs and their interactions than doctors do. It is their specialty, after all.
posted by geeky at 11:36 AM on July 16