NORLESTRIN FE 2.5/50
Clinical safety rating
cautionComprehensive clinical and safety monograph for NORLESTRIN FE 2.5/50 (NORLESTRIN FE 2.5/50).
Combination oral contraceptive containing norethindrone (progestin) and ethinyl estradiol (estrogen). Inhibits ovulation by suppressing gonadotropin-releasing hormone (GnRH) via negative feedback on the hypothalamus and pituitary. Increases cervical mucus viscosity to impede sperm penetration and induces endometrial atrophy to prevent implantation.
| Metabolism | Hepatic metabolism via cytochrome P450 (CYP) enzymes: ethinyl estradiol is primarily metabolized by CYP3A4; norethindrone undergoes reduction, hydroxylation, and conjugation. Both undergo enterohepatic recirculation and are excreted in urine and feces. |
| Excretion | Norethindrone: ~80% renal (as glucuronide and sulfate conjugates), ~20% fecal. Ethinyl estradiol: ~40% renal, ~60% fecal, with enterohepatic recirculation. |
| Half-life | Norethindrone: ~8-10 hours (terminal), requiring daily dosing for stable contraceptive effect. Ethinyl estradiol: ~13-21 hours (terminal), supporting once-daily administration. |
| Protein binding | Norethindrone: ~61-70% bound to albumin and SHBG. Ethinyl estradiol: ~97-98% bound to albumin. |
| Volume of Distribution | Norethindrone: Vd ~1.8-4.5 L/kg (extensive tissue distribution). Ethinyl estradiol: Vd ~2.5-5 L/kg (distributes into breast milk). |
| Bioavailability | Norethindrone: ~64% (oral). Ethinyl estradiol: ~38-48% (oral) due to first-pass metabolism. |
| Onset of Action | Oral: Requires 7 consecutive days of dosing for full contraceptive effect (ovarian suppression). |
| Duration of Action | 24 hours (maintained with daily dosing); missed pills reduce efficacy. |
| Molecular Weight | Ethinyl estradiol: 296.4 Da; Norethindrone: 298.4 Da |
One tablet orally once daily, each containing 2.5 mg norethindrone acetate and 50 mcg ethinyl estradiol, plus 7 iron tablets (75 mg ferrous fumarate) taken during the placebo week.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment provided; contraindicated in severe renal impairment (GFR <30 mL/min) due to potential fluid retention. |
| Liver impairment | Contraindicated in severe hepatic disease (Child-Pugh class C); use with caution in mild to moderate impairment (Child-Pugh A or B) with monitoring for adverse effects; no specific dose reduction guidelines established. |
| Pediatric use | Not indicated for use before menarche; post-menarche: same as adult dosing (one tablet daily) after menstrual cycle establishment. |
| Geriatric use | Not indicated for postmenopausal women; no dose adjustment in elderly with normal hepatic and renal function, but consider increased risk of thromboembolic events and metabolic effects. |
| 1st trimester | Contraindicated: Use during the first trimester is associated with an increased risk of birth defects, including cardiovascular and limb defects, due to the hormonal components. |
| 2nd trimester | Contraindicated: Use during the second trimester may increase the risk of fetal harm, including potential effects on fetal development, and is not recommended unless clearly needed. |
| 3rd trimester | Contraindicated: Use during the third trimester is contraindicated due to risks such as fetal feminization and other developmental effects. |
Clinical note
Comprehensive clinical and safety monograph for NORLESTRIN FE 2.5/50 (NORLESTRIN FE 2.5/50).
| Placental transfer | The hormones in Norlestrin FE 2.5/50 cross the placenta. Clinical evidence indicates significant transfer of ethinyl estradiol and norethindrone to the fetus. |
| Breastfeeding | Estrogens and progestins are excreted in breast milk in small amounts, potentially affecting the nursing infant. Use is generally not recommended during breastfeeding because of possible adverse effects on milk production and infant development. |
| Lactation Rating | L4 (Possibly Hazardous) |
| Teratogenic Risk | NORLESTRIN FE 2.5/50 (norethindrone acetate 2.5 mg/ethinyl estradiol 0.05 mg) is contraindicated in pregnancy. First trimester: increased risk of congenital anomalies including cardiovascular and limb defects, and possible non-genital malformations. Second/third trimester: feminization of male fetus, vaginal adenosis, and cervical changes in females. Exposure is associated with a 1.3 to 2.0-fold increased risk of congenital heart defects. |
| Fetal Monitoring | In case of inadvertent use during pregnancy, monitor for fetal development via ultrasound and assess for cardiovascular and urogenital abnormalities. Discontinue immediately if pregnancy is suspected or confirmed. |
| Fertility Effects | After discontinuation, return of fertility may be delayed but no permanent impairment. Post-pill amenorrhea may occur lasting up to 6 months. Does not cause infertility. |
■ FDA Black Box Warning
Cigarette smoking increases the risk of serious cardiovascular events (e.g., myocardial infarction, stroke, thromboembolism) from combination oral contraceptive use. Risk increases with age and number of cigarettes smoked. Women over 35 years who smoke should not use this combination oral contraceptive.
| Serious Effects |
Thrombophlebitis or thromboembolic disordersKnown or suspected pregnancyHistory of breast cancerUndiagnosed abnormal genital bleedingJaundice with prior oral contraceptive useHepatic adenoma or carcinomaKnown or suspected estrogen-dependent neoplasia
| Precautions | Thromboembolic disorders: increased risk of venous thromboembolism (VTE) and arterial thrombosis; discontinue if suspected, Cardiovascular disease: increased risk of myocardial infarction and stroke, especially in smokers >35 years, Hypertension: may develop or worsen; monitor blood pressure, Cervical cancer: controversial association; Pap smear screening recommended, Hepatic neoplasia: rare but reported; contraindicated with active liver disease, Gallbladder disease: increased risk of cholelithiasis, Ocular effects: retinal thrombosis may occur; discontinue if sudden partial or complete vision loss, Carbohydrate metabolism: may decrease glucose tolerance; monitor diabetic patients, Fluid retention: use with caution in conditions affected by edema (e.g., migraine, asthma, renal impairment) |
| Food/Dietary | Avoid grapefruit and grapefruit juice as they may increase estrogen levels and side effects. No specific food restrictions otherwise. Iron from ferrous fumarate may be affected by calcium-rich foods or supplements; take iron at least 2 hours apart from dairy products. |
| Clinical Pearls | NORLESTRIN FE 2.5/50 contains norethindrone 2.5 mg and ethinyl estradiol 50 mcg, plus ferrous fumarate (75 mg) as a placebo. The high estrogen dose (50 mcg) increases thromboembolic risk; avoid in patients with migraine with aura, hypertension, or smoking >35 years. Iron supplementation can cause dark stools. The formulation includes 7 iron-containing placebo tablets to maintain cycle control and prevent iron deficiency. |
| Patient Advice | Take one tablet daily at the same time, preferably after an evening meal to reduce nausea. · Missed dose: If one day, take as soon as remembered; if two days, take two tablets then resume schedule; if more, use backup contraception and consult healthcare provider. · Report signs of blood clots: chest pain, sudden shortness of breath, leg pain/swelling, or severe headache. · Iron supplements may cause dark stools; this is harmless. · Do not smoke while taking this medication as it increases risk of serious cardiovascular side effects. · Antibiotics (e.g., rifampin), anticonvulsants, and St. John's Wort may decrease effectiveness; use alternative contraception. |
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