NORETHIN 1/50M-21
Clinical safety rating
cautionComprehensive 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. |
| Molecular Weight | 298.42 |
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 | Avoid use during first trimester due to risk of congenital defects, particularly cardiovascular and limb anomalies. |
| 2nd trimester | Avoid use due to potential for virilization of female fetus and other adverse effects. |
| 3rd trimester | Avoid use due to potential for virilization of female fetus and other adverse effects. |
Clinical note
Comprehensive clinical and safety monograph for NORETHIN 1/50M-21 (NORETHIN 1/50M-21).
| Placental transfer | Norethindrone crosses the placenta and has been associated with fetal harm. |
| Breastfeeding | Norethindrone is excreted into breast milk in small amounts. Use during breastfeeding is generally not recommended as it may reduce milk production and affect infant development. Alternatives preferred. |
| Lactation Rating | L3 (Moderately Safe) or Avoid |
| 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. |
| 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. |
■ 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 pregnancyBreast cancer (current or history)Undiagnosed abnormal genital bleedingHepatic impairment or diseaseThromboembolic disordersCerebrovascular diseaseCoronary artery diseaseHypersensitivity to norethindrone or any component
| 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. |
| Food/Dietary | No significant food interactions. However, maintaining a consistent diet is recommended to avoid gastrointestinal upset. Grapefruit juice may inhibit CYP3A4 and increase estrogen levels, but clinical significance is low. |
| Clinical Pearls | Monitor for thromboembolic events, especially in smokers over 35. Advise use of barrier contraception to reduce STI risk. Assess blood pressure at baseline and follow-up due to potential estrogenic effects. May reduce menstrual flow and dysmenorrhea. |
| Patient Advice | Take one tablet daily at the same time, even if you do not have sex. · If you miss a pill, follow the package instructions or consult your healthcare provider. · Smoking while taking this pill increases risk of blood clots, especially if over age 35. · This pill does not protect against HIV or other sexually transmitted infections. · Contact your doctor if you experience severe headaches, vision changes, or leg pain/swelling. |
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