I?ve found several reports on research conducted on the impact on
contraceptive failure rates while using antibiotics. The statistics
are similar to what you recall reading. As I said in my earlier
clarifications, many of the literature reviews on this subject
conclude that there aren?t definitive findings on this subject. Below
I?ve included the articles confirming your general impressions as well
as the cautionary articles about the state of the current research.
Wishing you well for your projects.
~ czh ~
CONTRACEPTIVE FAILURE RATES WHILE USING ANTIBIOTICS
Vol. No: 29:01 Posted: 1/15/04
Potential Interactions Between Oral Contraceptives and Other
Medications and Natural Substances
Drugs That Increase the Metabolism of OCs
Anti-infective Agents: By increasing the metabolism of OCs,
anti-infective agents increase the likelihood of pregnancy. Although
antibiotics are commonly associated with decreased OC efficacy, not
all antibiotics affect OCs, and in many cases, the interactions have
not been proven clinically.3 A set of retrospective surveys found the
concomitant use of OCs and antibiotics had a contraceptive failure
rate of 1.2% to 1.6%.2 While this may seem large, the failure rate of
OCs with typical use, which can mean improper use, is about 5%.5
Recognition of the potential for drug and herbal products to interact
with OCs provides the pharmacist with the opportunity to help patients
make better and more educated decisions about using natural products
with their prescription drugs. By staying informed, pharmacists can
share information about new drug interactions with patients. As more
people opt for herbal remedies, such as red clover or St. John's wort,
instead of pharmaceutical agents to manage health conditions, new OC
drug interactions will come to light. Additionally, pharmacists need
to monitor professional materials to learn about OC interactions with
existing drugs. Not only can pharmacists educate their patients on
avoiding adverse effects but they can also dispel myths about drug
interactions, including the notion that all antibiotics decrease the
efficacy of OCs.
***** This article provides a comprehensive overview of the concurrent
use of oral contraceptives and other medications.
Interactions Between Oral Contraceptives and
Antifungals/Antibacterials: Is Contraceptive Failure the Result?
Author: Weisberg E.1
Source: Clinical Pharmacokinetics, Volume 36, Number 5, May 1999, pp. 309-313(5)
All women using combined oral contraceptives should be informed of the
very low level of risk of interactions with antimicrobials (probably
about 1%) and that it is not possible to identify who may be at risk.
Women concerned about this low level of risk should be given
information about the use of barrier methods or avoidance of
intercourse during the first 7 days of concomitant antimicrobial
therapy and for 7 subsequent days.
OC failure rates and oral antibiotics - oral contraceptives - JFP Journal Club
Journal of Family Practice, August, 1997 by Valerie J. King
Results The OC failure rate for combined OC and oral antibiotic use
was 1.6 pregnancies per 100 woman-years of exposure, compared with the
control group's failure rate of 0.96. The authors state that this
difference is not statistically significant (P = .4) but do not
provide 95% confidence intervals around each of these rates. Age group
weighting resulted in a rate of 1.3 pregnancies for subjects and 1.05
for controls. The five total pregnancies that occurred in the
antibiotic-exposed group were all among women in their 20s, and three
of the five occurred in unmarried women. All five had used OCs for at
least 6 months at the time of pregnancy and had been taking
antibiotics for at least 3 months. Three of the pregnancies were in
women taking minocycline, and the other two women were taking
cephalosporins. Overall, both the subject and control groups had lower
failure rates than the 3% that is generally reported for OC users.
Failure rates as high as 18% have been reported in particular groups
J Am Acad Dermatol. 1997 May;36(5 Pt 1):705-10. Related Articles, Links
Oral contraceptive failure rates and oral antibiotics.
Helms SE, Bredle DL, Zajic J, Jarjoura D, Brodell RT, Krishnarao I.
RESULTS: Five pregnancies occurred in 311 woman-years of combined
antibiotic/OC exposure (1.6% per year failure rate) compared with 12
pregnancies in 1245 woman-years of exposure (0.96% per year) for the
425 control patients. This difference was not significant (p = 0.4),
and the 95% confidence interval on the difference (-0.81, 2.1) ruled
out a substantial difference (> 2.1% per year). There was also no
significant difference between OC failure rates for the women who
provided data under both conditions, nor between the two control
groups. All our data groups had failure rates below the 3% or higher
per year, which are typically found in the United States. CONCLUSION:
The difference in failure rates of OCs when taken concurrently with
antibiotics commonly used in dermatology versus OC use alone suggests
that these antibiotics do not increase the risk of pregnancy.
Physicians and patients need to recognize that the expected OC failure
rate, regardless of antibiotic use, is at least 1% per year and it is
not yet possible to predict in whom OCs may fail.
OVERVIEW OF RESEARCH ON ANTIBIOTICS AND ORAL CONTRACEPTIVES
Antibiotics and Oral Contraceptive Failure
Kevin E. Burroughs, MD; M. Lee Chambliss, MD, MSPH
Arch Fam Med. 2000;9:81-82.
Are antibiotics related to oral combination contraceptive failures?
A MEDLINE search was performed (1966 to present, limited to the
English language) on the following medical subject heading (MeSH)
terms: antibiotics and contraceptives, oral, hormonal.
To date there have been few controlled studies and no prospective
randomized trials of the effects of antibiotics on combination oral
contraceptives. The literature does not specifically delineate
warnings between intravenous and oral contraceptives; therefore, the
same warnings would apply to both. Most of the available data do not
indicate any major reduction in the efficacy of OCPs with concurrent
common antibiotic use. However, these studies cannot reliably exclude
a small decrease in efficacy especially in the "low-dose" (<35 µg of
estrogen) combination OCPs. With several well-known resources
suggesting alternative contraception during antibiotic use,
pragmatically it is important to inform all female patients of the
Antibiotics and Oral Contraceptive Failure
Drug Interactions: Insights and Observations
Pharmacy Times November 2003
The available data produce this conclusion: In any given patient,
antibiotics are unlikely to impair the efficacy of oral
contraceptives. The data emphatically, however, do not establish that
any antibiotic can be used in any woman on any oral contraceptive
without increasing the risk of unintended pregnancy. Thus, only 2
possibilities are left: (1) antibiotics cause contraceptive failure in
a very small percentage of patients, or (2) antibiotics have no effect
on oral contraceptive efficacy. With the available data, it is simply
not possible to choose which of these 2 possibilities is correct, so
pharmacists must continue to warn patients accordingly.
For an electronic version of this article, including references if
any, visit www.hanstenandhorn.com.
Obstetrics & Gynecology 2001;98:853-860
© 2001 by The American College of Obstetricians and Gynecologists
Drug Interactions Between Oral Contraceptives and Antibiotics
METHODS OF STUDY SELECTION: A total of 167 articles were retrieved for
analysis. Another 32 articles were identified by review of the
references cited in these publications. Articles were selected based
on their ability to provide information on the relationship between
antibiotic therapy and OC efficacy in otherwise compliant users
(defined as women with unplanned pregnancies who reported compliance
with their OC regimen). Additionally, studies that either directly
measured the effects of antibiotics on the pharmacokinetics of OC
components, or that analyzed the effects of antibiotics on measures of
ovulation in OC users were accepted.
CONCLUSION: Rifampin impairs the effectiveness of OCs. Pharmacokinetic
studies of other antibiotics have not shown any systematic interaction
between antibiotics and OC steroids. However, individual patients do
show large decreases in the plasma concentrations of ethinyl estradiol
when they take certain other antibiotics, notably tetracycline and
penicillin derivatives. Because it is not possible to identify these
women in advance, a cautious approach is advised.
Birth control pill FAQ: From menstruation to menopause ? and everything in between
Can antibiotics decrease the effectiveness of birth control pills?
The effects of antibiotics on birth control pills may be overstated ?
except in the case of one antibiotic, rifampin. Studies clearly show
that rifampin decreases the effectiveness of birth control pills in
Hypothetically speaking, other antibiotics, particularly penicillin
and tetracycline derivatives, could impair the effectiveness of birth
control pills. However, no large studies have proved such an effect.
Researchers can't rule out the possibility that a small percentage of
women may experience decreased effectiveness of birth control pills
while taking an antibiotic. And if you're taking a newer, extremely
low-dose oral contraceptive, you could be more susceptible to these
potential effects from antibiotics. If you're concerned, consider
using a barrier method of contraception for the duration of your
antibiotic interference with oral contraceptives
antibiotics "oral contraceptives" failure rate