NORLESTRIN 21 1/50
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NORLESTRIN 21 1/50 (NORLESTRIN 21 1/50).
Combination oral contraceptive containing norethindrone (progestin) and ethinyl estradiol (estrogen). Inhibits ovulation via suppression of gonadotropins (LH, FSH). Enhances cervical mucus viscosity, reducing sperm penetration. Thins endometrium, decreasing implantation likelihood.
| Metabolism | Norethindrone: primarily hepatic via reduction and conjugation; also CYP3A4-mediated hydroxylation. Ethinyl estradiol: hepatic via CYP3A4, also undergoes sulfation and glucuronidation; enterohepatic recirculation. |
| Excretion | Norethindrone: renal (33% as metabolites), fecal (50%); ethinyl estradiol: renal (40% as glucuronide conjugates), fecal (60%) |
| Half-life | Norethindrone terminal half-life: 5-14 hours; ethinyl estradiol terminal half-life: 10-20 hours. Clinical context: steady-state reached within 5-7 days, clinically significant for missed dose management. |
| Protein binding | Norethindrone: 61% bound to albumin, 36% bound to SHBG; ethinyl estradiol: >97% bound to albumin. |
| Volume of Distribution | Norethindrone: 4.3 L/kg; ethinyl estradiol: 2.8-4.5 L/kg. Clinical meaning: extensive distribution into tissues, including breast and reproductive organs. |
| Bioavailability | Oral: norethindrone ~64% (first-pass metabolism), ethinyl estradiol ~45% (first-pass metabolism); transdermal and vaginal routes have higher bioavailability. |
| Onset of Action | Oral: contraceptive effect begins after 7 consecutive days of dosing; peak plasma levels achieved 1-2 hours post-dose. |
| Duration of Action | Contraceptive protection persists for 24 hours with daily dosing; after last dose, ovulation may return within 7-14 days. |
One tablet (1 mg norethindrone acetate/50 mcg ethinyl estradiol) orally once daily for 21 days, followed by 7 days off therapy.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for GFR ≥30 mL/min; avoid use in patients with GFR <30 mL/min due to potential fluid retention and hypertension. |
| Liver impairment | Contraindicated in Child-Pugh class B or C; use with caution in Child-Pugh class A with monitoring for adverse effects. |
| Pediatric use | Not indicated for use before menarche; dosing based on adult regimen for postmenarchal adolescents. |
| Geriatric use | Not indicated for postmenopausal women; avoid use in elderly due to increased risk of thrombotic events. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NORLESTRIN 21 1/50 (NORLESTRIN 21 1/50).
| Breastfeeding | Small amounts of ethinyl estradiol and norethindrone are excreted in breast milk (M/P ratio not established; estimated <1% of maternal dose). May reduce milk production and quality, especially with high doses. Use during breastfeeding is generally not recommended; alternative contraception advised for nursing mothers. |
| Teratogenic Risk | FDA Pregnancy Category X. Combination hormonal contraceptives (estrogen-progestin) are contraindicated during pregnancy due to association with fetal harm, including cardiovascular defects and limb reduction defects with first-trimester exposure. No increased risk of major malformations reported from inadvertent exposure in early pregnancy, but use is not indicated. Second and third trimester exposure may increase risk of neonatal jaundice and hepatic adenoma in the mother. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events (e.g., stroke, myocardial infarction) from COC use. Risk increases with age (especially >35 years) and number of cigarettes smoked. Women >35 who smoke should not use COCs.
| Serious Effects |
Hypersensitivity to any component. Thromboembolic disorders (current/history). Cerebrovascular or coronary artery disease. Known or suspected breast carcinoma. Endometrial carcinoma or other estrogen-dependent neoplasia. Undiagnosed abnormal genital bleeding. Cholestatic jaundice of pregnancy/jaundice with prior pill use. Hepatic adenoma/carcinoma. Known or suspected pregnancy. Active liver disease with abnormal function. Heavy smoking (>15 cigarettes/day) in women ≥35.
| Precautions | Increased risk of thromboembolic disorders (DVT, PE), stroke, MI. Hepatic neoplasia. Cigarette smoking. Hypertension. Gallbladder disease. Carbohydrate/lipid metabolism effects. Headache/migraine. Unscheduled bleeding. Depression. Ocular lesions (retinal thrombosis). Hepatic impairment. Pregnancy (must be ruled out before initiation). Lactation: may reduce milk production. |
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| Fetal Monitoring | None required as drug is contraindicated in pregnancy. In case of inadvertent use, monitor for fetal anomalies via ultrasound; no specific fetal monitoring protocol. Maternal monitoring includes blood pressure, liver function, and signs of thromboembolism. |
| Fertility Effects | Suppresses ovulation via gonadotropin inhibition. After discontinuation, return to fertility may be delayed by 1-3 months but no permanent impairment. No evidence of long-term fertility reduction. |