Comparative Pharmacology
Head-to-head clinical analysis: LOESTRIN 21 1 20 versus NORINYL 1 50 21 DAY.
Peer-Reviewed Evidence
Head-to-head clinical analysis: LOESTRIN 21 1 20 versus NORINYL 1 50 21 DAY.
LOESTRIN 21 1/20 vs NORINYL 1+50 21-DAY
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Combination estrogen-progestin contraceptive; suppresses gonadotropin secretion (FSH, LH) via negative feedback, inhibiting ovulation; increases cervical mucus viscosity and alters endometrial receptivity.
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, then 7 days off. 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
Norethindrone: 8-11 hours (terminal half-life; steady-state achieved after 5-10 days); Ethinyl estradiol: 13-27 hours (terminal half-life; significant interindividual variability due to enterohepatic recirculation).
Norethindrone: 5-8 hours; Ethinyl estradiol: 7-15 hours; steady-state reached within 5-7 days
Renal: ~50% (as metabolites, primarily glucuronide conjugates of norethindrone and ethinyl estradiol); Fecal: ~35% (via bile); Urinary recovery of unchanged drug is minimal (<1%).
Renal (40% as metabolites), fecal (50% as metabolites), <1% unchanged
Category C
Category C
Combined Oral Contraceptive
Combined Oral Contraceptive