MINASTRIN 24 FE
Clinical safety rating
cautionComprehensive 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). |
| Molecular Weight | 286.41 |
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 | Contraindicated in pregnancy. Use during the first trimester is associated with an increased risk of congenital anomalies, particularly neural tube defects and cardiovascular malformations. Effective contraception is required before initiation. |
| 2nd trimester | Contraindicated in pregnancy. There is no indication for use during the second trimester. Risk of fetal harm outweighs any potential benefit. |
| 3rd trimester | Contraindicated in pregnancy. Use during the third trimester may cause fetal harm, including potential for androgenic effects on female fetuses and premature closure of epiphyses. |
Clinical note
Comprehensive clinical and safety monograph for MINASTRIN 24 FE (MINASTRIN 24 FE).
| Placental transfer | Yes, crosses the placenta. Active transport and passive diffusion contribute to fetal exposure. Fetal serum levels may reach up to 10% of maternal levels. |
| Breastfeeding | Excreted into breast milk in small amounts. No adverse effects reported in nursing infants at therapeutic maternal doses. However, consider risk of potential androgenic effects in male infants and theoretical risk of virilization in female infants. Caution is advised; alternative agents may be preferred during breastfeeding. |
| Lactation Rating | L3 (Moderately Safe) |
| 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. |
| 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. |
■ 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 |
PregnancyKnown or suspected breast cancerActive thromboembolic disordersSevere hepatic impairmentHypersensitivity to minastrin or any component
| 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. |
| Food/Dietary | Grapefruit and grapefruit juice may increase ethinyl estradiol levels, potentially increasing side effects; avoid concurrent use. No other significant food interactions. Iron tablets should be taken with food to reduce gastrointestinal upset. |
| Clinical Pearls | MINASTRIN 24 FE is a combination oral contraceptive containing norethindrone acetate and ethinyl estradiol, with ferrous fumarate as a dietary supplement. It has a 24/4 regimen, which may reduce hormone-free interval symptoms. The iron tablets (ferrous fumarate) are placebo and do not affect contraception; they are intended to help offset iron loss during menstruation. Patients with a history of venous thromboembolism, migraine with aura, or certain cancers should not use this drug. Counsel patients to take at the same time daily. Breakthrough bleeding is common in the first few cycles. Missed pill management: if one active pill is missed, take it as soon as remembered, even if taking two in one day. If two or more active pills are missed, use backup contraception for 7 days. |
| Patient Advice | Take one tablet daily at the same time, preferably after the evening meal. The 24 light blue-green pills are active hormones; the 4 brown pills are iron supplements (placebo for contraception). · If you miss a pill, refer to the package insert or consult your healthcare provider. Missing pills increases pregnancy risk. · Common side effects include nausea, breast tenderness, headache, and spotting. These often improve after 2–3 cycles. · Do not smoke while taking this medication; smoking increases the risk of serious cardiovascular events, especially in women over 35. · This medication does not protect against HIV or other sexually transmitted infections. · Tell your healthcare provider about all medications you take, especially antibiotics, anticonvulsants, and St. John's wort, as they may reduce effectiveness. |
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