No, antibiotics do not affect IUDs such as Kyleena, Mirena, or Skyla. In fact, there are not many contraceptive devices or even contraceptives that are affected by antibiotics, despite popular belief that this is the case.

There are only two situations where antibiotics can affect ORAL contraceptives (not IUDs, injectable or implantable contraceptives). These are:

• If the antibiotic or the bacterial condition being treated with the antibiotic causes diarrhea or vomiting. This may reduce the time the oral contraceptive has to be absorbed, which may lower levels of contraceptive hormones in the body, increasing the risk of pregnancy
• If the antibiotic being given is either rifampin or rifabutin, and it is being given for 2 months or longer. Both these antibiotics induce (speed-up) the metabolism of liver enzymes, which can lower the blood levels of oral hormonal contraceptives.

Hormone-releasing IUDs such as Kyleena, Mirena, or Skyla work directly in the uterine cavity and do not rely on absorption through the stomach or metabolism through the liver for their effect, making drug interactions far less likely.

Why do people think that antibiotics affect contraceptives?

Research has shown that with combined oral contraceptives, the estrogen component (usually ethinyl estradiol) undergoes enterohepatic recirculation. This means that it is absorbed through the stomach wall and then metabolized in the liver to form inactive conjugates with glucuronide, which are then excreted back into the duodenum in the bile. Bacteria within our stomach and intestine then cleave (break apart) these conjugates, and the active estrogen is then reabsorbed and can exert its effects.

Researchers also had a theory that if these bacteria were suppressed or killed (which happens if you take a broad-spectrum antibiotic) then this would prevent these conjugates from being cleaved, which could result in lower than normal concentrations of estrogen which might cause contraceptive failure, increasing the risk of pregnancy.

However, subsequent research has shown two things. Firstly, the enterohepatic recirculation of estrogen is not important and large studies investigating women taking oral contraceptives in conjunction with non-enzyme inducing antibiotics have not shown any decreased levels of ethinyl estradiol nor an increased incidence of pregnancy. If diarrhea or vomiting does occur, then a woman should be advised to follow the “seven-day rule”, which means using other methods of contraception (eg, condoms or abstinence) until seven active pills have been taken and the diarrhea has ceased.

Secondly, that the only antibiotics that could affect oral hormonal contraceptives are those that induce enzymes, and currently, there are only two of these available, rifampin and rifabutin which are used to treat tuberculosis and meningitis. Women who take either rifampin or rifabutin for more than two months are advised to change from their oral contraceptive to another method (such as an implant or IUD) that is not affected by these medications.

How do hormone-releasing IUDs work?

Kyleena, Mirena, and Skyla work by releasing a continuous, low-dose of levonorgestrel (a progesterone hormone) which is thought to prevent pregnancy by thickening cervical mucus which prevents the passage of sperm into the uterus, inhibiting the motility of sperm and their survival, and changing the endometrium so it is unable to accommodate a fertilized egg.

What are the differences between Kyleena, Mirena, and Skyla?

Kyleena, Mirena, and Skyla are all T-shaped contraceptive devices that slowly release levonorgestrel and are placed inside a woman’s uterus to prevent pregnancy. The main differences between them are how long they last for, how much levonorgestrel they release, and the size of the device.

For more information about the differences between Kyleena, Mirena, and Skyla, see here.