MINASTRIN 24 FE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MINASTRIN 24 FE (MINASTRIN 24 FE).
Combination of an estrogen (ethinyl estradiol) and a progestin (norethindrone acetate) that inhibits gonadotropin release from the pituitary, suppressing ovulation, thickening cervical mucus, and altering endometrial receptivity.
| Metabolism | Ethinyl estradiol undergoes first-pass metabolism in the liver via CYP3A4 and is extensively conjugated with glucuronic acid and sulfate. Norethindrone acetate is deacetylated to norethindrone, which is metabolized primarily via reduction and conjugation. |
| Excretion | Urine (primarily as glucuronide conjugates; ethinyl estradiol and norethindrone metabolites) and feces. Approximately 40% of norethindrone metabolites are excreted in urine and 60% in feces. Ethinyl estradiol is excreted as glucuronide and sulfate conjugates in urine (40%) and feces (60%). |
| Half-life | Norethindrone: 7-8 hours; ethinyl estradiol: 13-27 hours. Clinical context: Steady-state achieved within 5-10 days; half-life supports once-daily dosing. |
| Protein binding | Norethindrone: 61% bound to albumin and SHBG; ethinyl estradiol: 97-98% bound to albumin (not SHBG). |
| Volume of Distribution | Norethindrone: 4.0 L/kg; ethinyl estradiol: 15-20 L/kg (distributes extensively into tissues; no specific clinical significance beyond high distribution). |
| Bioavailability | Oral: Norethindrone ~64% (first-pass metabolism reduces bioavailability); ethinyl estradiol ~40% (variable due to presystemic conjugation). |
| Onset of Action | Oral: 24 hours (suppression of ovulation requires 7 days of continuous dosing; contraceptive effect begins after 7 days). |
| Duration of Action | 24 hours (daily dosing maintains contraceptive efficacy; missed pill guidelines apply if >24 hours). |
One tablet orally once daily for 24 weeks, followed by 4 placebo tablets. Each tablet contains 1 mg norethindrone acetate and 20 mcg ethinyl estradiol for 21 days, then 1 mg norethindrone acetate and 0.75 mg ferrous fumarate for 7 days.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment guidelines; use with caution in patients with renal impairment. Monitor for fluid retention and hypertension. |
| Liver impairment | Contraindicated in patients with hepatic impairment (Child-Pugh class B or C). For mild hepatic impairment (Child-Pugh class A), use with caution and monitor liver function. |
| Pediatric use | Not approved for use before menarche. After menarche, same adult dosing applies for adolescents: one tablet orally daily. |
| Geriatric use | Not indicated for use after menopause. In elderly women of reproductive age, same adult dosing applies; consider increased risk of thromboembolic events. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MINASTRIN 24 FE (MINASTRIN 24 FE).
| Breastfeeding | Small amounts of progestins and estrogens are excreted in breast milk. M/P ratio not established. Use with caution in nursing mothers; may reduce milk production and quality. Consider alternative contraception. |
| Teratogenic Risk | First trimester: No increased risk of major birth defects based on epidemiological studies. Second and third trimesters: Use may cause fetal harm due to potential androgenization of female fetuses and other adverse effects from progestin exposure. Discontinue if pregnancy occurs. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events from combined hormonal contraceptive use. Women over 35 who smoke should not use this drug.
| Serious Effects |
Thrombophlebitis or thromboembolic disorders; history of deep vein thrombosis or pulmonary embolism; cerebrovascular or coronary artery disease; known or suspected breast cancer; endometrial cancer or other estrogen-dependent neoplasia; undiagnosed abnormal genital bleeding; cholestatic jaundice of pregnancy or jaundice with prior oral contraceptive use; hepatic adenoma or carcinoma; known or suspected pregnancy; hypersensitivity to any component; age >35 and smoking.
| Precautions | Increased risk of thromboembolic disorders, including venous thromboembolism, myocardial infarction, and stroke; highest in smokers >35 years. Use caution in patients with hypertension, diabetes, hyperlipidemia, migraine with aura, or history of cholestatic jaundice. Discontinue if jaundice, visual disturbances, or sudden severe headache occurs. |
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| Fetal Monitoring |
| Monitor for pregnancy before initiation and if dose is missed. Perform liver function tests and monitor blood pressure periodically. Assess for thromboembolic events. Fetal monitoring includes ultrasound for growth and anomalies if exposure occurs during pregnancy. |
| Fertility Effects | Reversible suppression of ovulation. After discontinuation, normal fertility typically returns within 1-3 months. No permanent effects on fertility. |