CONTRACEPTIVES AND PHENYTOIN
Combined hormonal contraceptives and possibly progestogen-only oral contracep- tives are less reliable during treatment with phenytoin. Inter-menstrual breakthrough bleeding and spotting can take place, and pregnancies have occurred. Controlled studies have shown that phenytoin can reduce contraceptive steroid levels. Similarly, emergency hormonal contraceptives are considered to be less effective in those taking phenytoin. Fosphenytoin, a prodrug of phenytoin, may interact similarly.
The increase in failure rate appears small, but because of the consequences of an
unwanted pregnancy, especially with drugs that may cause foetal abnormalities,
adjustments should be made. If possible, change to another suitable,
non-interacting antiepileptic. For general advice on the use of enzyme inducers,
such as phenytoin, and contraceptives, see contraceptives. Reliable
contraception in most patients is said to be achievable with 80 to 100 micrograms
of ethinylestradiol daily. Additional barrier methods are considered the most
appropriate option for the short-term use of enzyme-inducing antiepileptics.
The increase in failure rate appears small, but because of the consequences of an
unwanted pregnancy, especially with drugs that may cause foetal abnormalities,
adjustments should be made. If possible, change to another suitable,
non-interacting antiepileptic. For general advice on the use of enzyme inducers,
such as phenytoin, and contraceptives, see contraceptives. Reliable
contraception in most patients is said to be achievable with 80 to 100 micrograms
of ethinylestradiol daily. Additional barrier methods are considered the most
appropriate option for the short-term use of enzyme-inducing antiepileptics.