Ethinylestradiol levels are reduced by fosamprenavir with
ritonavir, lopinavir/
ritonavir, nelfinavir and
ritonavir alone, and norethisterone levels are slightly reduced by fosamprenavir with
ritonavir,
lopinavir/ritonavir, nelfinavir and
tipranavir in patients taking combined oral
contraceptives. Concurrent use of hormonal contra- ceptives with
amprenavir is not recommended, as
amprenavir levels are reduced. There is no direct information about progestogen-only pills but since lopinavir/
ritonavir and nelfinavir cause small reductions in the levels of norethisterone (given as part of a combined oral contraceptive) it is possible that these
protease inhibitors could reduce the contraceptive
efficacy of progestogen-only oral
contraceptives containing norethisterone. The
efficacy of emergency hormonal
contraceptives may also be decreased.
There have been unconfirmed reports of contraceptive failure in patients taking indinavir, nelfinavir,
ritonavir and saquinavir. To avoid this potential risk, and the risk of breakthrough bleeding, it has been suggested that a contraceptive preparation with a higher dose of ethinylestradiol or an alternative or additional non-hormonal form of contraception should be used during and for one cycle after
ritonavir is stopped. Similar advice applies to other
protease inhibitors given with
ritonavir. Note that the progestogen-only oral
contraceptives have a higher failure rate than the combined oral
contraceptives. Despite the lack of evidence it would seem prudent to use additional contraceptive measures in this situation as well. For additional advice on the use of
enzyme inducers, such as
protease inhibitors, and
contraceptives, see
contraceptives. Note that whatever other methods of contraception are being used, barrier methods are also advisable to reduce the risk of HIV
transmission.