Will This Antibiotic Interfere With My Birth Control?


January in North Carolina means the common cold and the flu kick into high gear. Over the past few weeks, I have seen an increase of prescriptions for antibiotics and cough syrups come to the Campus Health Pharmacy for sick students. Almost every day, I have been asked whether taking antibiotics will interfere with birth control.

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Image courtesy of by Nate Grigg on Flickr

The issue of whether or not antibiotics interfere with the effectiveness of birth control has been a controversial topic for many years. To provide a quick review, there are many forms of birth control that contain both an estrogen and a progestin – pharmacists call these combined hormonal contraceptives.

Combined hormonal contraceptives include:

  • The pill (Yaz, Tri-Sprintec, Cryselle, Heather, etc.)
  • The patch (Ortho Evra)
  • The ring (NuvaRing)

Combined hormonal contraceptives use multiple mechanisms to reduce the possibility of pregnancy. Estrogen suppresses the release of hormones from the pituitary. Progestin suppresses ovulation and thickens cervical mucus to prevent sperm from entering the upper genital tract. Progestin provides most of the contraceptive effects in hormonal contraceptive methods.

Broad-Spectrum Antibiotics and Common Antifungals = OK

Antibiotics routinely used to fight illnesses are the “broad-spectrum” antibiotics. These drugs are called “broad-spectrum” because they can be used to treat a variety of infections caused by many different organisms. These antibiotics include:

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Image courtesy of Global Panorama onFlickr
  • Amoxicillin
  • Azithromycin
  • Clarithromycin
  • Metronidazole
  • Quinolones (ciprofloxacin, ofloxacin)
  • Doxycycline

Common antifungal agents frequently used to treat vaginal yeast infections include:

  • Fluconazole
  • Miconazole

The Centers for Disease Control and Prevention (CDC) classifies broad-spectrum antibiotics and antifungals as category 1 interactions with contraceptives. This means that the CDC has determined that when using a broad-spectrum antibiotic or antifungal, there is no restriction to using them in combination with combined hormonal contraception. Many groups agree with the CDC, including the American College of Obstetricians and Gynecologists. Broad-spectrum antibiotics have not been found to reduce the concentration of hormones in the combined hormonal contraceptives to a sub-therapeutic level that could increase the risk of pregnancy. Therefore, a backup method of birth control is not required for women using combined hormonal contraceptives and broad-spectrum antibiotics. Even patients who may be on a long-term antibiotic, such as erythromycin for acne, will not require a backup method of birth control when taking both the antibiotic and their normal form of birth control.

Enzyme Inducers = Use a backup method

This being said t is still important to ask your pharmacist about whether or not your antibiotic is considered “broad-spectrum,” because there are some antibiotics that do significantly interact with combined hormonal contraceptives.

Antibiotics that are known to definitely affect the efficacy of combined hormonal contraceptives are called “enzyme inducers” because they essentially make your body chew up the hormones in the birth control faster than normal. These types of antibiotics include the following:

  • Rifampin (including some combination antibiotics that contain rifampin)
  • Rifabutin
  • Griseofulvin (used to treat fungal infections)

Rifampin, Rifabutin and griseofulvin are antibiotics known to reduce the levels of hormones in the pill, the patch or the ring. It is very important that women on these antibiotics who also use combined hormonal contraception use a backup method of birth control while they are taking these antibiotics. The CDC has classified these antibiotics as category 3 interactions with combined hormonal contraceptives because when used together, the effectiveness of the birth control is reduced and pregnancy risk is increased.

Remember:

No method of birth control is guaranteed to be 100% effective even when taken correctly and even when using category 1 antibiotics.

Using your contraceptive method correctly, no matter which antibiotic you may need to take, increases the efficacy of the contraceptive method and reduces the risk of pregnancy. Here are some methods recommended by the CDC for how to ensure that your method of birth control is the most effective:

  • If you are taking a pill, make sure to take the pill every day and at the same time every day.
  • If you are using a patch, make sure the patch stays in place and that you change the patch on time, once per week.
  • If you are using a vaginal ring, make sure to remove and replace the ring on time as directed.

When in doubt…

Ask your pharmacist! All of the pharmacists in the Campus Health Pharmacy, located in the basement of Campus Health Services James A. Taylor building, and the Student Stores Pharmacy, located on the third floor of the UNC Student Stores, are happy to talk to you about any questions or concerns you may have. The pharmacists are here to provide further education on how to appropriately take your method of birth control, what to do if you miss a dose, or whether or not you should use a backup method of birth control while you need to take a certain antibiotic for an infection. Asking questions and staying informed is the best way to ensure your health needs are being met.

Jordan Wood is a 4th-year student pharmacist at the UNC Eshelman School of Pharmacy. She grew up just down the road in Hillsborough and attended UNC-Chapel Hill for her undergraduate degree. In her free time, she enjoys horseback riding and baking. 

References:

  1. Hatcher, R. A. (2011). Combined Oral Contraceptives (COCs). Contraceptive Technology(p. 303). New York: Ardent Media Inc.
  2. Centers for Disease Control and Prevention (CDC). (2010). Appendix B: Classifications for Combined Hormonal Contraceptives. Retrieved from http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5904a3.htm
  3. ACOG practice bulletin. No. 73: Use of hormonal contraception in women with coexisting medical conditions. Obstet Gynecol. 2006;107(6):1453-72

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