Contraceptives and antibiotics: how do they interact?

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Oral hormonal contraceptives, also known as contraceptive pills, act by preventing ovulation in the menstrual cycles of women who take them and, therefore, preventing pregnancy from occurring. Taking antibiotics can affect the effectiveness of these contraceptives. Therefore, if you do not want to get pregnant, it is important that you inform yourself well of the interaction between both compounds.

Below you have an index with all the points that we will discuss in this article.

Index

Contraceptives and antibiotics: how do they interact?

Previous concepts

Before analyzing the effect of taking antibiotics on contraceptives, it is important to make clear what they are and what their role is.



What is a hormonal contraceptive?

These are drugs that usually combine two active principles corresponding to two female hormones:

  • Estrogens (estradiol)
  • Progestin (progesterone)

For this reason, they are known as combined oral contraceptives (ACO). However, there are also oral hormonal contraceptives that contain only progestin.

This type of contraceptives alter the hormonal regulation of the menstrual cycle. In this way, the release of the ovum is prevented and the cervical mucus is altered, making it difficult for the sperm to reach the ovule. The uterine lining is also modified, making implantation of the embryo more complicated.

Most ACOs contain 21 tablets with active ingredient and 7 tablets that do not contain medication, known as placebo. The last 7 pills are given so that the woman does not lose the routine of taking a daily pill and knows when she has to start again a new blister pack or package. During these 7 pills is when you should lower menstrual bleeding, which will be mild and short-lived due to the hormonal situation.

There are also boxes that contain only 21 pills, leaving 7 days off in which the woman should not take anything. The risk of this type of presentation of the contraceptive is that the woman forgets some intake and the contraceptive effect decreases.



What is an antibiotic?

An antibiotic is a medicine indicated to fight infections caused by bacteria. Its main function is to kill bacteria or prevent their reproduction.

It is important to keep in mind that antibiotics act only in the presence of a bacterial and non-viral infection. In addition, taking antibiotics can reduce part of our "good" bacterial flora, so its generic use is not recommended for any infection.

Interaction between contraceptives and antibiotics

When the ingestion of a contraceptive pill is combined with other medications, an interaction between both can occur that prevents the adequate absorption of the contraceptive and loses its effectiveness. This would lead to an increase in the probability of pregnancy.

Reduced contraceptive efficacy

The basic compounds of contraceptives and antibiotics are metabolized in the liver. Therefore, consuming them at the same time could cause a decrease in the concentration of hormone absorbed by the body and, with it, the reduction of contraceptive efficacy and the possibility of ovulation occurring and with it, an unwanted pregnancy.

However, the majority of studies conducted in this regard do not observe a significant loss of the contraceptive effect in those women who are treated with antibiotics, with the exception of one type of antibiotic: rifampicin.

Based on the scientific evidence of the effect of the antibiotic on the contraceptive, we distinguish three main groups or categories:

  • Category A: in this group we find rifampicin. It is the only antibiotic that has been shown to reduce plasma levels of estrogen.
  • Category B: ampicillin, amoxicillin, metronidazole, penicillin and tetracycline are the antibiotics included in this category. They have been infrequently related to a reduction in the effectiveness of the contraceptive.
  • Category C: antibiotics such as cephalexin, clindamycin, dapsone, erythromycin, griseofulvin, isoniazid, trimethoprim and the quinolones are some of those that have shown interaction very rarely or in isolated cases.

Although not all antibiotics influence the contraceptive effect, many specialists embrace "prevention is better than cure" and, therefore, recommend using an additional barrier contraceptive (such as a condom) in cases where it is combined the administration of any type of antibiotic with a hormonal contraceptive.

It is advisable to follow these indications not only during the treatment with the antibiotic but also in the 7 days after the end of the same, that is, 7 days after the withdrawal of the antibiotic drug. What should not be done is to abandon the intake of the contraceptive pill so as not to alter the hormonal pattern.

If the woman should take the antibiotic treatment for a long period of time, an alternative contraceptive method should be prescribed to safely avoid the unwanted pregnancy.

Questions from users

Are there any symptoms that indicate that the antibiotic is reducing the effectiveness of the contraceptive?

Intermenstrual bleeding (metrorrhagia), that is, between one menstruation and the next, may be caused by a hormonal imbalance. This is unusual during hormonal treatment with contraceptives because, if taken properly, the regulation is strict. Therefore, bleeding out of place may indicate a failure in such regulation, perhaps caused by the interaction with the antibiotic.

Is this interaction only with oral contraceptives or also with other types of hormonal contraceptives?

Although most studies refer to oral contraceptives, indications regarding the effect of antibiotics generally apply to other types of hormonal contraceptives such as injections, subdermal implants, vaginal ring and patches.

In addition to antibiotics, are there any other medications that can affect the hormonal regulation of birth control pills?

Whenever a woman goes to take a medication during the contraceptive treatment it is advisable that she consult with the specialist the possible interaction between both. This advice is given, not only because of the possibility of pregnancy due to the loss of contraceptive effectiveness, but also because the contraceptive could reduce the effect of the indicated medication.

In addition to rifampicin, other drugs that show interaction with oral contraceptives are anticonvulsants such as phenytoin, phenobarbital, primidone, bitobarbital, carbamazepine, ethosuximide or methylphenolbarbital.

For other specific medications, as we have already mentioned, it is advisable to consult with the doctor, because there is little clarity of the studies and also, there may be specific changes due to the situation of each woman.

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