#Grand Rounds

Are Drug Interactions between Antibiotics and Hormonal Birth Control a Reality or Myth?

BACKGROUND AND PURPOSE:

Limited data regarding hormonal contraception and antibiotics
Rifamycin antibiotics (rifampin, rifabutin) induce key hepatic enzymes that are part of hormonal birth control pathway metabolism but this mechanism may not be generalizable to other more common antibiotics
There is data that most pharmacists recommend backup contraception for women who use antibiotics with hormonal contraception due to concern for unintended pregnancy
Simmons et al. (AJOG, 2018) sought to examine potential interactions between non-rifamycin antibiotics and hormonal contraceptives

Systematic review
- Search included trials, cohort, case-control, and pharmacokinetic studies when non-rifamycin antibiotics and hormonal contraceptive that addressed:
- pregnancy rates
- pharmacodynamics
- pharmacokinetic outcomes
Reviews were independently assessed by two authors to avoid bias
Risk of bias was assessed using the USPSTF evidence grading system
Findings were tabulated by drug class

Study quality ranged from good to poor and addressed only oral contraceptive pills, emergency contraception pills, and the combined vaginal ring
Ethinyl estradiol was affected when administered with dirithromycin (a macrolide) and showed increased clearance but this effect was not seen with any other drug
Two studies demonstrated no difference in pregnancy rates in women who used oral contraceptives with and without non-rifamycin antibiotics
There was no observed differences in ovulation suppression or breakthrough bleeding in any study that combined hormonal contraceptives with any antibiotic
No significant decreases in any progestin pharmacokinetic parameter occurred during co-administration with any antibiotic

Clinical and pharmacokinetic outcome studies do not support the existence of a drug interaction between hormonal birth control and non-rifamycin antibiotics
Authors do note that
- There may be individual differences in drug metabolism and they suggest a small subset of women (likely <1%) may be at risk for hormonal contraceptive failure when taking antibiotics
- Switching to another contraceptive or backup method if compliance is good and there is an unintended pregnancy
- Obesity may play a role in drug metabolism that could impact these study results

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