Impact of Combined Hormonal Contraceptives on UPA

Emergency contraception (EC) provides women with an additional line of defense against unintended pregnancy during an act of unprotected intercourse. An antiprogestin, ulipristal acetate (UPA; ellaTM), has emerged as one of the most effective oral options. However, there is currently a lack of information regarding the practical use of UPA. Basic science studies have shown that UPA binds to and prevents progesterone receptor from working, leading to the possible concern that hormonal contraceptives, like the birth control pill, would prevent UPA from working. Ideally, women should start their regular method of birth control soon after EC use but by doing this, they may prevent the UPA EC from working. A woman could just delay starting her regular method of birth control but then she is still at risk for pregnancy.

This proposal has been designed to address this gap in knowledge and will focus on the impact of the birth control pill on UPA's ability to delay ovulation (or the release of an egg). Subjects will undergo a referent cycle UPA only (Cycle 1, 1 month), followed by a washout cycle (Cycle 2, 1 month) and finally UPA with combined oral contraceptives (COCs) dosed 2 days later (Cycle 3, 1 month treatment cycle). The hypothesis is that starting the birth control pill shortly after UPA adversely impacts UPA's ability to delay ovulation.

Inclusion criteria

• Generally healthy women aged 18 to 35 with regular menses (every 21-35 days).
• Normal BMI
• Proven ovulation with a screening serum progesterone of >3ng/mL
• Willing to use condoms (if sexually active with a male partner), willing to not have sex with men during the study, or have had a tubal ligation (or have a partner who has had a vasectomy) or have a copper intrauterine device (IUD).

Exclusion criteria

• Known intolerance or allergy to any of the study medication
• Known metabolic disorders including polycystic ovarian syndrome or uncontrolled thyroid disorder
• Overweight or obese BMI
• Any Centers for Disease Control and Prevention (CDC) Medical eligibility criteria category 3 or 4 for combined oral contraception (COC) use 12.
• Pregnancy, breastfeeding, or seeking pregnancy; recent (8 week) use of hormonal contraception
• Current use of drugs that interfere with metabolism of sex steroids
• Smokers.