Efficacy of emergency contraception may be reduced when taken with other medicines
Women seeking the Norlevo or Levodonna emergency contraceptives should be aware that the efficacy may be reduced when taken with other medicines.
The contraceptive efficacy of levonorgestrel-containing emergency contraceptives may be reduced if they are taken with other medicines or herbal medicines affecting the metabolism of levonorgestrel. For example, medicines used to treat fungal infections, epilepsy, tuberculosis and HIV as well as herbal medicines containing St John’s wort.
Consequently, doctors and pharmacies should advise women who are seeking levonorgestrel-containing emergency contraception to use alternative contraception, e.g. a copper intrauterine device, if they have used enzyme-inducing medicine or herbal medicines within the last 4 weeks (mainly inducers of CYP3A4 enzymes).
If this is not an option, they should be advised to double the usual dose of levonorgestrel from 1.5mg to 3mg. Women are also recommended to have a pregnancy test since some enzyme-inducing medicines have been associated with birth defects.
Medicines which may affect levonorgestrel levels
The following medicines may affect contraceptive efficacy of emergency contraception:
- Some medicines to treat epilepsy, e.g. Barbiturates (phenemal), primidone, phenytoin or carbamazepine
- Some medicines to treat tuberculosis, e.g. rifampicin, rifabutin
- Some medicines to treat HIV, e.g. ritonavir, efavirenz
- Some medicines to treat fungal infections, e.g. griseofulvin
- Herbal medicines containing St John’s wort (Hypericum perforatum)
The above medicines or herbal medicines are liver enzyme inducers, mainly inducers of CYP3A4 enzymes, that may increase metabolism of levonorgestrel. This may lead to a reduction in plasma levonorgestrel levels and may thus reduce contraceptive efficacy.
The European Commission has decided that the current summaries of product characteristics for emergency contraceptives should be updated. The amendments to the product information will be made as soon as possible.