NORETHIN 1/50M-21
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NORETHIN 1/50M-21 (NORETHIN 1/50M-21).
Norethindrone is a progestin that suppresses gonadotropin release from the pituitary, inhibiting ovulation. It also induces endometrial changes and increases cervical mucus viscosity, impeding sperm penetration.
| Metabolism | Hepatic metabolism primarily via reduction and conjugation; minor CYP3A4 involvement. Metabolites are excreted in urine and feces. |
| Excretion | Renal: 50-60% as metabolites; Fecal: 30-40% (via biliary); Less than 5% unchanged in urine. |
| Half-life | Terminal elimination half-life: 5-14 hours (mean ~8h). Clinical context: Steady-state achieved after 4-5 days; dosing interval 24 hours maintains therapeutic levels. |
| Protein binding | 97-98% bound; primarily to albumin (70%) and SHBG (30%). |
| Volume of Distribution | 3.6-4.7 L/kg; indicates extensive tissue distribution, including breast tissue and adipose. |
| Bioavailability | Oral: 64-76% (first-pass metabolism reduces bioavailability). |
| Onset of Action | Oral: 2-4 hours for progestogenic effects; contraceptive effect achieved after 7 consecutive days of dosing. |
| Duration of Action | Duration: Approximately 24 hours. Clinical notes: Once-daily dosing maintains continuous contraceptive coverage; withdrawal bleeding occurs 2-3 days after last active pill. |
One tablet (norethindrone 1 mg and ethinyl estradiol 50 mcg) orally once daily for 21 days, followed by 7 days of placebo.
| 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 fluid retention. |
| Liver impairment | Contraindicated in hepatic impairment, including active liver disease, jaundice, or Child-Pugh class B or C. No studies for mild impairment; use not recommended. |
| Pediatric use | Not indicated for use before menarche. Post-menarche, use same dosing as adults (one tablet daily) with monitoring for thromboembolic risks. |
| Geriatric use | Not indicated for postmenopausal women. In older reproductive-age women, use same adult dosing; monitor for cardiovascular and thromboembolic risks due to higher estrogen dose. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NORETHIN 1/50M-21 (NORETHIN 1/50M-21).
| Breastfeeding | Excreted in breast milk in small amounts (estrogen and progestin). M/P ratio not established for this fixed-dose combination. May reduce milk production and composition, especially in early postpartum. American Academy of Pediatrics considers use compatible with breastfeeding, but alternative contraception recommended. Monitor infant for jaundice and weight gain. |
| Teratogenic Risk | Contraindicated in pregnancy. First trimester: Association with cardiovascular defects and limb reduction defects (case-control studies show odds ratio 1.3-2.8 for oral contraceptive use). Second and third trimesters: No increased risk of major malformations if inadvertently exposed; however, hormones can affect fetal endocrine development. Use is not recommended during any trimester. |
■ FDA Black Box Warning
Cigarette smoking increases the risk of serious cardiovascular side effects from combined oral contraceptives. This risk increases with age and with heavy smoking (≥15 cigarettes per day) and is marked in women over 35 years who smoke. Combined oral contraceptives should not be used by women over 35 years who smoke.
| Serious Effects |
Known or suspected pregnancy, history of or current thrombophlebitis or thromboembolic disorders, cerebrovascular disease, coronary artery disease, hepatic impairment or liver tumors, undiagnosed abnormal uterine bleeding, known or suspected breast carcinoma (unless for palliation), hypersensitivity to norethindrone.
| Precautions | Increased risk of thromboembolic disorders, especially in smokers over 35. Hepatotoxicity risk. May cause fluid retention. Monitor for depression, elevated blood pressure, and glucose intolerance. Discontinue if jaundice or visual disturbances occur. |
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| Fetal Monitoring | If inadvertently exposed during pregnancy, perform detailed fetal anatomy ultrasound at 18-20 weeks. Monitor maternal blood pressure and glucose tolerance throughout pregnancy. No specific fetal monitoring required beyond routine prenatal care. |
| Fertility Effects | Suppresses ovulation via inhibition of gonadotropin release. Return to fertility is usually prompt after discontinuation (median time to ovulation 1-2 cycles). No permanent adverse effects on fertility. May improve menstrual regularity in some women. |