Comparative Pharmacology
Head-to-head clinical analysis: ESTROSTEP 21 versus NORINYL 1 50 21 DAY.
Peer-Reviewed Evidence
Head-to-head clinical analysis: ESTROSTEP 21 versus NORINYL 1 50 21 DAY.
ESTROSTEP 21 vs NORINYL 1+50 21-DAY
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Estrostep 21 is a combination oral contraceptive containing ethinyl estradiol and norethindrone acetate. It works primarily by suppressing gonadotropin-releasing hormone (GnRH) from the hypothalamus, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion from the pituitary, thereby inhibiting ovulation. Additionally, it thickens cervical mucus to impede sperm penetration and alters the endometrium to reduce implantation likelihood.
Norinyl 1+50 21-Day contains norethindrone (a progestin) and mestranol (an estrogen). Mestranol is converted to ethinyl estradiol, which provides negative feedback on gonadotropin release, inhibiting ovulation. Norethindrone suppresses gonadotropins and alters cervical mucus and endometrial lining to prevent implantation.
One tablet orally once daily for 21 days, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg.
One tablet (1 mg norethindrone + 0.05 mg mestranol) orally once daily for 21 days, followed by 7 placebo tablets. Start on day 1 of menstrual cycle or first Sunday after onset.
None Documented
None Documented
Ethinyl estradiol: 13-27 hours (terminal); norethindrone acetate: 5-14 hours (terminal). Steady-state achieved within 3-5 days.
Norethindrone: 5-8 hours; Ethinyl estradiol: 7-15 hours; steady-state reached within 5-7 days
Biliary/fecal (40-50% as metabolites) and renal (30-40% as glucuronide and sulfate conjugates)
Renal (40% as metabolites), fecal (50% as metabolites), <1% unchanged
Category C
Category C
Combined Oral Contraceptive
Combined Oral Contraceptive