This updated Medicines Q&A provides advice on a suitable oral contraceptive that can be used in a woman using an enzyme-inducing anti-epileptic or anti-tubercle drug.
For women taking very potent enzyme inducers such as rifampicin, the preferred method of contraception would be an IUD, LNG-IUS or an injectable such as DMPA. This is because drugs which induce hepatic enzymes are unlikely to affect the pharmacokinetics of DMPA or LNG-IUS.
This method should also be considered as first-line for other enzyme-inducing drugs (such as carbamazepine or phenytoin); however with these there is also some scope to consider other methods instead. Choice of an alternative method also depends upon the length of time the patient will be taking the enzyme-inducing drug.
For short term use of enzyme-inducing AEDs (<2 months), a minimum of 30 micrograms ethinylestradiol (EE) pill continuously or tricycle with a shortened 3 or 4 day pill-free interval (PFI), can be used for the duration of treatment and for a further 28 days (with additional precautions such as the use of condoms).
For longer term use (>2 months) of a hepatic enzyme-inducing AED, a daily dose of at least 50 micrograms of oestrogen (usually ethinylestradiol (EE)) should be used (to a maximum of 70 micrograms). This is taken continuously or as a tricycing regimen with a PFI of 4 days for the duration of treatment and a further 28 days.
Regional Medicines Information Manager, London Medicines Information Service