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#Grand Rounds

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

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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 

METHODS: 

  • 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 

RESULTS: 

  • 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 

CONCLUSION: 

  • 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 

Learn More – Primary Sources: 

Drug interactions between non-rifamycin antibiotics and hormonal contraception: a systematic review 

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