NORETHIN 1/50M-28
Clinical safety rating
cautionComprehensive clinical and safety monograph for NORETHIN 1/50M-28 (NORETHIN 1/50M-28).
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.
| Metabolism | Hepatic via CYP3A4; norethindrone is metabolized to various metabolites, primarily 5α-dihydro- and 3α,5β-tetrahydro compounds; estradiol is metabolized to estrone and estriol via 17β-hydroxysteroid dehydrogenase and conjugation. |
| Excretion | 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. |
| Half-life | 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. |
| Protein binding | Approximately 97% bound to plasma proteins, primarily albumin and sex hormone-binding globulin (SHBG). The binding affinity to SHBG is moderate, and unbound (free) fraction is about 3%. |
| Volume of Distribution | The apparent volume of distribution is approximately 2-4 L/kg, indicating extensive distribution into tissues. The Vd is consistent with binding to plasma proteins and distribution to adipose tissue. |
| Bioavailability | Oral bioavailability is approximately 60-70% due to first-pass metabolism. Micronized formulations may have slightly higher bioavailability. There is no clinically relevant absorption through other routes for this oral formulation. |
| Onset of Action | When used as an oral contraceptive, the onset of action for contraceptive effect is immediate if started on day 1 of menses; if started later, backup contraception is needed for 7 days. For endometriosis, clinical effects may take several months. |
| Duration of Action | The duration of action is 24 hours for contraceptive efficacy with daily dosing. Steady-state hormone levels are maintained with consistent daily intake. Missed doses reduce efficacy; withdrawal bleeding occurs during the placebo week. |
| Molecular Weight | 340.46 |
One tablet orally once daily for 28 consecutive days per menstrual cycle. Each tablet contains 1 mg norethindrone and 50 mcg ethinyl estradiol.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. Contraindicated in severe renal impairment or acute renal failure due to potential estrogen-induced fluid retention and hyperkalemia. |
| Liver impairment | Contraindicated in patients with Child-Pugh class B or C hepatic impairment (moderate to severe liver disease) due to impaired steroid hormone metabolism. Use with caution in Child-Pugh class A; consider alternative contraception. |
| Pediatric use | Not indicated for use before menarche. In post-menarchal adolescents (16-18 years), dose is same as adult: one tablet daily. Safety and efficacy not established in younger adolescents. |
| Geriatric use | Not indicated for use after menopause. Elderly patients have increased risk of thromboembolic events, cardiovascular disease, and breast cancer; use lowest effective dose if required, but generally avoid estrogen-containing contraceptives in women over 50 years. |
| 1st trimester | Contraindicated. Risk of fetal harm due to hormonal effects. Use only if benefit outweighs risk. |
| 2nd trimester | Contraindicated. Potential for virilization of female fetus. Avoid during pregnancy. |
| 3rd trimester | Contraindicated. May cause feminization of male fetus and other hormonal disturbances. |
Clinical note
Comprehensive clinical and safety monograph for NORETHIN 1/50M-28 (NORETHIN 1/50M-28).
| Placental transfer | Norethindrone crosses the placenta. Fetal plasma levels are about 50% of maternal levels after administration. |
| Breastfeeding | Small amounts of norethindrone are excreted in breast milk. Monitor infant for jaundice, breast enlargement, or other hormonal effects. Consider alternative contraception if breastfeeding. |
| Lactation Rating | L3 - Moderately Safe (limited data, potential risk to infant) |
| Teratogenic Risk | First trimester: No major teratogenic effects reported at recommended doses; postmarketing studies do not show increased risk of birth defects. Second and third trimesters: Avoid use due to risk of fetal harm including masculinization of female fetuses (norethindrone is a progestin). Use during pregnancy is contraindicated for routine contraception. |
| Fetal Monitoring | Monitor blood pressure regularly. Assess for signs of thromboembolism, especially in women with risk factors. No routine fetal monitoring required unless used inadvertently during pregnancy. |
| Fertility Effects | Reversible inhibition of ovulation; fertility returns to baseline within 1-2 cycles after discontinuation. No permanent effects on fertility. |
■ FDA Black Box Warning
Cigarette smoking increases the risk of serious cardiovascular events from combined hormonal contraceptives. Risk increases with age and heavy smoking (≥15 cigarettes/day). Women over 35 who smoke should not use this product.
| Serious Effects |
PregnancyHistory of thrombophlebitis or thromboembolic disordersHepatic tumors (benign or malignant)Undiagnosed abnormal genital bleedingKnown or suspected breast cancerHypersensitivity to norethindrone or any component
| Precautions | Thrombotic disorders (thrombophlebitis, pulmonary embolism), Cerebrovascular disease, Myocardial infarction, Liver disease, Elevated blood pressure, Gallbladder disease, Carbohydrate/lipid effects, Depression, Fluid retention |
| Food/Dietary | Grapefruit and grapefruit juice may increase plasma levels of norethindrone and mestranol, potentially increasing side effects. Avoid excessive consumption. No other significant food interactions known. |
| Clinical Pearls | NORETHIN 1/50M-28 is a monophasic oral contraceptive containing norethindrone 1 mg and mestranol 50 mcg. Administer at the same time daily; missed doses increase breakthrough bleeding and pregnancy risk. Consider drug interactions with anticonvulsants (e.g., phenytoin, carbamazepine), rifampin, and some antibiotics (e.g., griseofulvin, tetracyclines). Monitor for thromboembolic events, especially in smokers >35 years. Not recommended in patients with liver disease, thrombophilia, or breast cancer history. |
| Patient Advice | Take one pill daily at the same time, preferably after the evening meal or at bedtime. · If you miss a pill, follow the package instructions; use backup contraception if needed. · Common side effects include nausea, headache, breast tenderness, and breakthrough bleeding. · Seek medical attention for severe abdominal pain, chest pain, headache, vision changes, or leg pain/swelling. · Do not smoke while taking this medication, especially if over 35 years old. · Inform your doctor about all medications you are taking, including antibiotics and herbal supplements. |
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