LOESTRIN 24 FE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for LOESTRIN 24 FE (LOESTRIN 24 FE).
Combination estrogen-progestin contraceptive. Suppresses gonadotropin (FSH, LH) release via negative feedback, inhibiting ovulation. Increases cervical mucus viscosity, reducing sperm penetration. Alters endometrial development, decreasing implantation likelihood.
| Metabolism | Ethinyl estradiol undergoes CYP3A4-mediated hydroxylation and glucuronidation; norethindrone is metabolized via reduction, glucuronidation, and sulfation, primarily by CYP3A4 and CYP2E1. |
| Excretion | Ethinyl estradiol and norethindrone are primarily excreted in urine (about 50-60%) and feces (about 30-40%) as glucuronide and sulfate conjugates after hepatic metabolism. |
| Half-life | Norethindrone: 5-12 hours; Ethinyl estradiol: 13-27 hours. The terminal half-life supports once-daily dosing; steady state is achieved within 5-7 days. |
| Protein binding | Norethindrone: ~97% bound, primarily to sex hormone-binding globulin (SHBG) and albumin. Ethinyl estradiol: ~97% bound, primarily to albumin and SHBG. |
| Volume of Distribution | Norethindrone: approximately 3.6 L/kg; Ethinyl estradiol: approximately 2.7 L/kg. Large Vd indicates extensive tissue distribution (reproductive organs, liver, fat). |
| Bioavailability | Norethindrone: approximately 64% (oral) due to first-pass metabolism. Ethinyl estradiol: approximately 55% (oral) due to first-pass metabolism and intestinal conjugation. |
| Onset of Action | Oral administration: Contraceptive effect begins after 7 consecutive days of dosing; if started on day 1 of menses, immediate protection. |
| Duration of Action | 24 hours for contraceptive coverage; consistent daily dosing required. Missed pills reduce efficacy; if dose is delayed >12 hours, backup contraception is recommended. |
One tablet (1 mg norethindrone acetate/20 mcg ethinyl estradiol) orally once daily for 24 days, followed by a low-dose iron-containing tablet (75 mg ferrous fumarate) for 4 days.
| Dosage form | TABLET |
| Renal impairment | No dosage adjustment required for mild to moderate renal impairment. Not recommended for use in patients with severe renal impairment or end-stage renal disease due to lack of data. |
| Liver impairment | Contraindicated in patients with hepatic disease, including acute hepatitis, hepatic adenomas, or cirrhosis. No dose adjustment recommendations; avoid use. |
| Pediatric use | Approved for use in postmenarchal females. Dosage same as adults: one active tablet daily for 24 days followed by iron-containing tablets for 4 days. Not indicated for premenarchal females. |
| Geriatric use | Not indicated for use in postmenopausal women. No specific dosing recommendations; therapy should be discontinued if menopause occurs. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for LOESTRIN 24 FE (LOESTRIN 24 FE).
| Breastfeeding | Small amounts of contraceptive steroids and/or metabolites have been identified in breast milk. M/P ratio not established. Use may reduce milk production and composition. Not recommended during breastfeeding; consider alternative contraception. |
| Teratogenic Risk | First trimester: Postmarketing studies have not shown an increased risk of birth defects with oral contraceptives. Second and third trimesters: Contraindicated due to potential adverse effects on fetal development including possible estrogenic effects on fetal genitalia. Discontinue if pregnancy occurs. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events (thrombosis, myocardial infarction, stroke) from combination oral contraceptives, especially in women over 35 who smoke >15 cigarettes/day.
| Serious Effects |
Thrombophlebitis/thromboembolic disorders, cerebrovascular or coronary artery disease, known or suspected pregnancy, undiagnosed abnormal genital bleeding, known/suspected breast cancer, hepatic tumors (benign/malignant), hypersensitivity to any component, smoking >15 cigarettes/day in women >35 years.
| Precautions | Thrombotic disorders, hypertension, gallbladder disease, hepatic neoplasia, retinal thrombosis, carbohydrate/lipid effects, headache, menstrual irregularities, depression, hereditary angioedema. |
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| Fetal Monitoring |
| No specific maternal-fetal monitoring required beyond routine prenatal care if inadvertent exposure occurs. Pregnancy testing is recommended if pregnancy is suspected during use. |
| Fertility Effects | No permanent effects on fertility. Normal ovulation and fertility return upon discontinuation. Transient delay in return to fertility possible after cessation. |