Reader,

I seek medical facts regarding the following issue.

I am on the birth control pill Ortho Tri-Cyclen. I have recently been
prescribed to an antibiotic: amoxicillin. I have just recently
finished a 10 day dosage of amoxicillin. On the 9th day of my
antibiotic, I finished my 3-week dosage of birth control and started
the 1-week of placebo pills.

1. How antibiotics such as this one affect birth control pills such as
Ortho Tri-Cyclen with regards to pregnancy prevention
2.  I would like to know the minimum time to wait before I can have
unprotected intercourse without the increased risk of pregnancy. Of
course I know there is always a risk of pregnancy while on the pill.

I would strongly prefer medical resources from or similar to
www.webmd.com (that is, reliable facts, not opinion).

Thank you.

Hello jgortner~

According to the Mayo Clinic, ?Certain antibiotics, such as rifampin
(Rifadin), amoxicillin (Amoxil), metronidazole (Flagyl), tetracycline
(Sumycin) and cephalexin (Keflex), may decrease the effectiveness of
birth control pills. However, no large studies have confirmed this.
Though the evidence is weak, the possibility that this can occur in a
very small percentage of women can't be ruled out.? (?Birth control
pill: The right form of birth control for you?? by the Mayo Clinic
staff, http://www.mayoclinic.com/invoke.cfm?objectid=287D1ABE-1807-41DF-A121B6D1FF492B12
)

However, in another section of Mayo?s site, they state: ?Studies
clearly show that rifampin decreases the effectiveness of birth
control pills in preventing ovulation. Anecdotal evidence suggests
this effect may also occur with other antibiotics, such as:
Amoxicillin, Metronidazole, Tetracycline, Cephalexin, Erythromycin,
Isoniazid ? (Emphasis mine. ?Birth control pills: Can antibiotics
decrease their effectiveness?? by the Mayo Clinic staff,
http://www.mayoclinic.com/invoke.cfm?id=AN00099 )

They conclude: ?Consider using a barrier method of contraception such
as a condom while taking antibiotics.?

Very few sites specify how long a woman should use a back-up method of
birth control, but according to BC Health Files, you should ?continue
to use the barrier form of birth control for two weeks after you
finish the antibiotics.? (?Oral Contraceptives (Birth Control Pills)
and Antibiotics,? Ministry of Health Planning,
http://www.bchealthguide.org/healthfiles/hfile38d.stm )


Regards,
Kriswrite

KEYWORDS USED:
"Birth Control pill" antibiotics
http://www.answers.google.com/answers/threadview?id=300371#a

"Birth Control" antibiotics 
http://www.answers.google.com/answers/threadview?id=300371#a

---

Request for Answer Clarification by jgortner-ga on 26 Jan 2004 13:02 PST

Thank you for you very well thought out answer.

The focus of my question was how long I must wait after stopping
antibiotics to have unprotected sex. You did answer this, but only
with one source.

I would like multiple sources for how long I must wait, instead of
just the one you quoted. If possible please find a couple more.

I do appriciate your time and energy in this matter. Thank you.

---

Clarification of Answer by kriswrite-ga on 26 Jan 2004 14:10 PST

No problem! I was just giving what I felt was the more credible
source.  Here ya go:

According to drugstore.com: ?To help women avoid pregnancy while
taking an antibiotic--and for at least one week afterward--doctors
generally recommend they use a condom or spermicide as a back-up
method of birth control.?   (?Do antibiotics interact with birth
control pills?,? Ask Your Pharmacist, Drugstore.com,
http://www.drugstore.com/qxa1091_333181_sespider-do_antibiotics_interact_with_birth_control_pills.htm
)


?The effectiveness of the pill will be reduced for the first 3 weeks
that you take the antibiotics. You should use extra precautions, such
as condoms for this time, but then you can trust the pill again,? says
another U.K. site (?Acne & Birth Control Pills,? Student Health,
http://www.studenthealth.co.uk/problemPage/Acne%20and%20Birth%20Control%20Pills.htm
)


The Oregon State University health site says, ?However, you may want
to consider a backup method for the duration of the antibiotic plus 7
days?? (?General Birth Control Pill Counseling Points,? OSU Health
Center, http://www.wm.edu/OSA/Health/general_birth_control.html )

On a Google cache page for Brown University: ?While the risk is very
low, we encourage women to use condoms for the duration of their
antibiotic prescription and for the following 7 days.? (?Birth Control
Pills,? Health Services, Brown University, temporarily found at:
://www.google.com/search?q=cache:pLYTIv_xTQwJ:www.brown.edu/Student_Services/Health_Services/Health_Education/Sexual_Health/Contraceptive_Options/Birth_Control_Pills.htm+%22Birth+Control%22+antibiotics+&hl=en&ie=UTF-8
)

About.com suggests a longer time period, and while they give a very
credible source, they are the only site I can find recommending this
length: ??the recommendations from the journal Contraceptive
Technologies include the use of an alternative contraceptive for the
longer of either the length of antibiotic therapy or 14 days, plus 7
additional days. This plan should be implemented on Day 1 of
antibiotic therapy.? (?5 Reasons For Contraceptive Failure,? Women?s
Health, About.com, http://womenshealth.about.com/cs/birthcontrol/l/blcontraceptfai.htm
)


Also, I see that somehow the links in the ?Keywords Used? section
somehow got messed up when I copied and pasted my Answer. Here?s what
they should look like:

"Birth Control pill" antibiotics
://www.google.com/search?hl=en&ie=ISO-8859-1&q=%22Birth+Control+pill%22+antibiotics&btnG=Google+Search

"Birth Control" antibiotics 
://www.google.com/search?hl=en&lr=&ie=ISO-8859-1&q=%22Birth+Control%22+antibiotics+&btnG=Google+Search

Simply put: Exactly what I was looking for. Very quick response on the
clarification. A+ answer.