Comparative Pharmacology
Head-to-head clinical analysis: NORETHIN 1 35E 28 versus NORINYL 1 50 21 DAY.
Peer-Reviewed Evidence
Head-to-head clinical analysis: NORETHIN 1 35E 28 versus NORINYL 1 50 21 DAY.
NORETHIN 1/35E-28 vs NORINYL 1+50 21-DAY
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Combination estrogen-progestin oral contraceptive. Ethinyl estradiol suppresses FSH and LH, preventing ovulation. Norethindrone alters cervical mucus and endometrial lining, inhibiting sperm penetration and implantation.
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 28 days (21 active tablets containing norethindrone 1 mg and ethinyl estradiol 35 mcg, followed by 7 inert tablets).
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: terminal elimination half-life approximately 8-11 hours. Ethinyl estradiol: terminal elimination half-life approximately 10-20 hours (mean ~13 hours). Clinical context: Steady-state achieved within 5 days; once-daily dosing maintains therapeutic levels.
Norethindrone: 5-8 hours; Ethinyl estradiol: 7-15 hours; steady-state reached within 5-7 days
Norethindrone is excreted primarily in urine as glucuronide and sulfate conjugates, with about 50-60% excreted renally; approximately 20-30% is excreted in feces via biliary elimination. Ethinyl estradiol is excreted in urine (40-60%) and feces (20-40%) after enterohepatic recirculation.
Renal (40% as metabolites), fecal (50% as metabolites), <1% unchanged
Category C
Category C
Combined Oral Contraceptive
Combined Oral Contraceptive