Ritonavir Hormonal contraceptives

Although information is limited, the pharmacokinetic interaction between the ethinylestradiol component of combined hormonal contraceptives and nelfinavir or ritonavir appears to be established and is likely to be clinically important. Similar decreases in plasma levels of ethinylestradiol caused by other drugs have resulted in reduced efficacy and reliability of combined oral contraceptives, and one retrospective report suggests that this has occurred with nelfinavir. It seem likely that the reduced contraceptive levels seen with fosamprenavir, lopinavir and tipranavir were due to the concurrent use of ritonavir (as would be common in practice). Similarly, although no interaction was reported with saquinavir, and raised contraceptive steroid levels were reported with amprenavir and atazanavir, in practice these drugs would be given with ritonavir (as a pharmacokinetic enhancer), and so the levels of combined hormonal contraceptives can reasonably be expected to be reduced. The Faculty ofFamily Planning... 

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