Possible drug interactions

Ulipristal acetate e.g. ellaOne®

FSRH Clinical Guideline: Emergency Contraception (March 2017, amended July 2023) has been updated to include more detailed advice on delaying versus immediate starting combined oral contraception (COC) after ulipristal acetate (UPA) EC use.

If UPA-EC is chosen, hormonal contraception should not generally be started for 5 days after the UPA-EC has been taken.

There is one exception to this. In the specific situation in which combined oral contraceptive pills are restarted after a scheduled hormone-free interval and then pills are missed later in the first week of pill taking, use of LNG-EC should be considered but if UPA-EC is chosen, pill-taking can be resumed immediately.

• Increase the metabolism of estradiol and progestogens and the efficacy of CHC may be reduced.
• Risks of CHC use and taking liver enzyme inducing drugs outweigh potential benefits (UKMEC 3) and an alternative method unaffected by enzyme inducing drugs is recommended.
• Further information regarding the effects of CHC on other medications
  can be found in FSRH CEU Guidance: Drug Interactions with Hormonal Contraception (May 2022)

• Short term (< 2months) liver enzyme inducing drug use:
  Can continue using CHC but they should be advised to use additional contraceptive precautions (e.g. condoms) while taking the enzyme-inducing drug and for 28 days after stopping treatment. To minimise the risk of contraceptive failure the CEU recommends an extended regimen (taking CHC continuously or tricycling with a shortened pill-/patch- or ring-free interval of 4 days.

• Long term liver enzyme inducing drug use:
  If still chooses to use COC as a long-term method, she should use a regime containing at least 50 micrograms of Ethinylestradiol.
  A 50 micrograms EE dose may be made up from an appropriate 30 micrograms plus 20 micrograms preparation.
  An extended or tricycling regime with a pill-free interval of 4 days should be followed Additional contraception is not required.
  If women are on Rifampicin or Rifabutin, an alternative method of contraception should be advised as the regimen above may not be effective.
• Breakthrough bleeding:
  This may indicate low serum EE concentrations. If other causes (e.g. chlamydia) have been excluded, the dose of EE can be increased up to a maximum of 70 micrograms EE.
• For women using the combined contraceptive patch or ring, information should be given on the use of alternative contraceptive methods if liver enzyme-inducers are to be used long term. The use of two patches or two rings is not recommended.

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Please note that Lamotrigine is not a liver enzyme inducing drug and that use of CHC in women taking antiepileptic drugs is UKMEC1.

However the estrogen in CHC can reduce Lamotrigine levels which may result in change in seizure frequency.  Therefore women on lamotrigine should not start CHC without informing their neurologist.

Withdrawal of CHC in a client already on lamotrigine can result in Lamotrigine toxicity, and patients should be made aware of this.

Further information is available in the Lamotrigine SPC which is available on line.

Non-enzyme inducing antibiotics: The CEU no longer advises that additional precautions are required to maintain contraceptive efficacy when using antibiotics with combined hormonal methods.
However if the antibiotics (and/or the illness) caused vomiting or diarrhoea, then the usual additional precautions relating to these conditions should be observed.

Rifampicin: Women who are given Rifampicin short term (.e.g. for meningococcal meningitis prophylaxis) should be advised to use the barrier method in addition to COC during treatment and for 28 days after stopping Rifampicin.

Orlistat (Xenical/Alli) – these may cause diarrhoea and reduce absorption. Additional precautions are advised in these situations.