Comparative Pharmacology
Head-to-head clinical analysis: NORETHIN 1 50M 28 versus NORINYL 1 50 21 DAY.
Peer-Reviewed Evidence
Head-to-head clinical analysis: NORETHIN 1 50M 28 versus NORINYL 1 50 21 DAY.
NORETHIN 1/50M-28 vs NORINYL 1+50 21-DAY
Comparing the clinical profiles, pharmacokinetic behaviors, and safety indices of these two therapeutic agents.
Norethindrone is a synthetic progestin that binds to the progesterone receptor, suppressing gonadotropin release and inhibiting ovulation. Estradiol provides negative feedback on the pituitary to reduce FSH and LH secretion, preventing follicular development.
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 consecutive days per menstrual cycle. Each tablet contains 1 mg norethindrone and 50 mcg 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
The terminal elimination half-life of norethindrone is approximately 7-8 hours following oral administration. Steady-state concentrations are achieved within 5-7 days. The half-life may be prolonged in patients with hepatic impairment.
Norethindrone: 5-8 hours; Ethinyl estradiol: 7-15 hours; steady-state reached within 5-7 days
Norethindrone (NET) and its metabolites are primarily excreted via the kidneys (50-70%) and feces (20-40%) as glucuronide and sulfate conjugates. Approximately 30-50% of an oral dose is recovered in urine within 24 hours, with extensive enterohepatic recirculation prolonging elimination.
Renal (40% as metabolites), fecal (50% as metabolites), <1% unchanged
Category C
Category C
Combined Oral Contraceptive
Combined Oral Contraceptive