4. An OC with a novel estrogen
Even as use of intrauterine devices and contraceptive implants continues to grow, OCs remain the reversible contraceptive most used by US women. While OCs have been widely studied and represent a safe method of contraception for most reproductive-age women, combination estrogen-progestin OCs are well recognized to increase the risk of VTE. Although the primary role of the progestin component of combination OCs is to suppress ovulation, estrogen is included in combination OCs to stimulate endometrial proliferation, thereby causing predictable bleeding. EE, the potent synthetic estrogen used in the great majority of current OC formulations, induces hepatic production of prothrombotic proteins while inhibiting synthesis of antithrombotic proteins. While the lower EE doses (10–35 µg) in today’s OC formulations are associated with a lower VTE risk than older OCs that contained higher doses of estrogen, VTE continues to represent the principal health risk associated with use of combination OCs. Accordingly, development of a combination OC that has less impact on risk of VTE would be appealing.
In April 2021, the FDA approved an OC formulation that combines 15 mg of the novel estrogen estetrol with 3 mg of drospirenone (Nextstellis). This dose of drospirenone is the same as that used in commonly prescribed EE/drospirenone OC formulations. Also known as E4, estetrol is a natural estrogen synthesized by the fetal liver. Plant-derived E4 is used in this new OC.
Depending on the tissue, E4 acts differently than other estrogens. Similar to other estrogens, E4 acts as an agonist on the nuclear receptor to produce beneficial effects in bone, vaginal mucosa, and heart.8 Unlike other estrogens, E4 inhibits proliferation of mammary gland cells and has a neutral impact on the liver.9
In contrast with EE, E4 is not inhibited by the liver’s P450 enzymes; accordingly, the risk of drug-drug interactions is reduced. Because E4 is primarily excreted through the urine and not through the biliary tract, the risk of gallstone formation may be lower than with an EE OC. Likewise, E4 has substantially less impact on triglycerides, which are increased with EE. Finally, because of E4’s reduced effect on the liver, the impact on clotting parameters is less than that observed with an OC formulated with EE.10 This latter observation raises the possibility that VTE risk is lower with the E4/drospirenone OC than an OC formulated with EE.
A 13-cycle phase 3 trial of the E4/drospirenone OC conducted in the United States and Canada enrolled 1,864 women aged 16 to 50 years, including 1,674 who were aged 16 to 35 years.11 Among women in this latter age group, the PI was 2.65 per 100 woman-years. Bleeding/cycle control patterns were similar to those observed in recent trials of other combination contraceptives. Likewise, the proportion of trial participants who discontinued the study due to adverse effects was similar to or lower than that noted in recent trials of other combination contraceptives. Of particular note, no cases of VTE were noted among trial participants of any BMI, a finding which contrasts with recent phase 3 trials of other combination contraceptives. The result of this pivotal trial suggests that the theoretic advantages of E4 when used in a combination OC formulation may translate into a safer, effective, and well-tolerated contraceptive.
Refinements in hormonal contraceptives continue
The 4 new short-acting hormonal contraceptives we reviewed represent enhancements on existing pills, patches, and rings. We hope that, financially, women will have access to these innovative methods and, in particular, that third-party payers will facilitate women’s access to these enhanced short-acting hormonal contraceptives. ●