Comparative Pharmacology
Head-to-head clinical analysis: NORETHIN 1 35E 21 versus NORINYL 1 50 21 DAY.
Peer-Reviewed Evidence
Head-to-head clinical analysis: NORETHIN 1 35E 21 versus NORINYL 1 50 21 DAY.
NORETHIN 1/35E-21 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; suppresses gonadotropin release from pituitary, inhibits ovulation, thickens cervical mucus, alters endometrial lining.
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.
1 tablet orally once daily for 21 days, followed by 7 days off, then repeat. Each tablet contains 1 mg norethindrone acetate and 0.035 mg ethinyl estradiol.
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 half-life ~7-8 hours (range 5-12 h). Ethinyl estradiol: terminal half-life ~13-27 hours (mean ~17 h). The half-life supports once-daily dosing with stable serum concentrations achieved after 3-5 days.
Norethindrone: 5-8 hours; Ethinyl estradiol: 7-15 hours; steady-state reached within 5-7 days
Norethindrone and ethinyl estradiol are primarily excreted via urine (approximately 60-80% as metabolites) and feces (about 10-30%). Renal excretion accounts for the majority, with biliary/fecal elimination contributing a minor but significant fraction.
Renal (40% as metabolites), fecal (50% as metabolites), <1% unchanged
Category C
Category C
Combined Oral Contraceptive
Combined Oral Contraceptive