LOESTRIN 24 FE
Clinical safety rating
cautionComprehensive 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. |
| Molecular Weight | Ethinyl estradiol: 296.4 Da; Norethindrone acetate: 340.5 Da |
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 | Combination hormonal contraceptives are contraindicated during pregnancy. Use in early pregnancy is not associated with an increased risk of birth defects, but continued use is not recommended. |
| 2nd trimester | Avoid use; no established safety; potential risks from estrogen and progestin exposure. |
| 3rd trimester | Avoid use; theoretical risks of adverse fetal effects, including feminization of male fetuses with progestins. |
Clinical note
Comprehensive clinical and safety monograph for LOESTRIN 24 FE (LOESTRIN 24 FE).
| Placental transfer | Estrogens and progestins cross the placenta; degree of transfer varies but is generally low to moderate. |
| Breastfeeding | Combination hormonal contraceptives can reduce milk production and quality; use is generally not recommended until breastfeeding is well-established (at least 6 weeks postpartum). Small amounts of hormones are excreted in milk, but no adverse effects on infant development have been reported with low-dose formulations. |
| Lactation Rating | L4 (Possibly Hazardous) |
| 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. |
| 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. |
■ 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 |
PregnancyCurrent or history of venous thromboembolismActive or history of arterial thromboembolic disease (e.g., stroke, MI)Known thrombophilic disordersUncontrolled hypertensionDiabetes with vascular involvementHeadaches with focal neurological symptoms or migraine with aura (age ≥35)Current or history of breast cancer or estrogen-dependent neoplasiaActive liver disease or hepatic adenomaMajor surgery with prolonged immobilizationSmoking in women over 35 years of age
| Precautions | Thrombotic disorders, hypertension, gallbladder disease, hepatic neoplasia, retinal thrombosis, carbohydrate/lipid effects, headache, menstrual irregularities, depression, hereditary angioedema. |
| Food/Dietary | No specific food interactions. Grapefruit juice may increase ethinyl estradiol levels; avoid excessive consumption. Alcohol does not affect efficacy but may worsen side effects like nausea or dizziness. The ferrous fumarate in placebo pills may be absorbed better with vitamin C (e.g., orange juice). |
| Clinical Pearls | Loestrin 24 Fe contains norethindrone acetate and ethinyl estradiol with 24 active tablets and 4 ferrous fumarate placebo tablets. It is approved for contraception and acne vulgaris in women ≥16 years. The shortened hormone-free interval (4 vs 7 days) may reduce breakthrough bleeding and improve ovarian suppression. Counsel patients that the iron tablets are not active hormone and serve only to maintain routine. If a dose is missed, the patient should take the missed pill as soon as remembered and continue the remaining pills, possibly requiring backup contraception. Breakthrough bleeding is common in the first few cycles; rule out pregnancy if persistent. |
| Patient Advice | Take one pill daily at the same time, preferably after a meal to reduce nausea. · The 4 brown pills contain iron; they are not hormonal and are taken during the placebo week. · Use backup contraception (condoms) for the first 7 days if starting for the first time or after a break. · Missing pills increases risk of pregnancy; follow package instructions for missed doses. · Do not smoke while taking this medication, especially if over 35 years old, due to increased risk of blood clots. · Report severe abdominal pain, chest pain, shortness of breath, headache, visual changes, or leg pain/swelling. · Regular gynecological exams and blood pressure monitoring are recommended. · Store at room temperature away from moisture and heat. |
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