MICROGESTIN 1/20
Clinical safety rating
cautionComprehensive clinical and safety monograph for MICROGESTIN 1/20 (MICROGESTIN 1/20).
Combination oral contraceptive containing estrogen (ethinyl estradiol) and progestin (norethindrone acetate). Inhibits gonadotropin secretion (FSH, LH) via negative feedback, preventing ovulation. Also causes cervical mucus thickening and endometrial thinning.
| Metabolism | Ethinyl estradiol metabolized primarily by CYP3A4 via hydroxylation; also conjugated with sulfate and glucuronic acid. Norethindrone acetate deacetylated to norethindrone, then metabolized by reduction and conjugation; CYP3A4 minor role. |
| Excretion | Renal: 40% as metabolites, 20% as glucuronide and sulfate conjugates; Fecal: 35%; Biliary: <5%. |
| Half-life | Norethindrone: 5.2-12.8 hours (mean ~8 hours); Ethinyl estradiol: 7-20 hours (mean ~13 hours); hepatic impairment prolongs. |
| Protein binding | Norethindrone: 60-80% bound to SHBG and albumin; Ethinyl estradiol: 95-98% bound to albumin. |
| Volume of Distribution | Norethindrone: 3.4-5.5 L/kg; Ethinyl estradiol: 2.6-4.4 L/kg; reflects extensive tissue distribution. |
| Bioavailability | Oral: Norethindrone 64-70%; Ethinyl estradiol 38-48% (first-pass metabolism). |
| Onset of Action | Oral: 7 days of continuous dosing for full contraceptive effect. |
| Duration of Action | 24 hours; requires daily dosing for continuous contraceptive coverage. |
| Molecular Weight | 340.46 |
| Action Class | Oral Contraceptive; Estrogen/Progestin Combination |
One tablet (norethindrone acetate 1 mg / ethinyl estradiol 20 mcg) orally once daily for 21 consecutive days, followed by 7 days of placebo or no tablets.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment recommended; data limited. Use caution in patients with significant renal impairment due to potential fluid retention. |
| Liver impairment | Contraindicated in severe hepatic disease (Child-Pugh C) due to impaired steroid metabolism. Use lowest effective dose in mild to moderate impairment (Child-Pugh A/B) with close monitoring. |
| Pediatric use | Not indicated for use before menarche. Post-menarche: same as adult dosing (one tablet daily) with monitoring for adverse effects. |
| Geriatric use | Not indicated for use after menopause due to increased risk of thromboembolic events and cardiovascular complications. |
| 1st trimester | Avoid use; oral contraceptives are associated with a slight increased risk of cardiovascular malformations; use is not recommended during pregnancy. |
| 2nd trimester | Avoid use; no known indication for oral contraceptives during second trimester; theoretical risk of adverse effects on fetal development. |
| 3rd trimester | Avoid use; oral contraceptives may cause withdrawal bleeding and are not indicated during pregnancy; potential effects on fetal gonadal development. |
Clinical note
Comprehensive clinical and safety monograph for MICROGESTIN 1/20 (MICROGESTIN 1/20).
| Placental transfer | Ethinyl estradiol and norethindrone cross the placenta; metabolites present in fetal tissues. |
| Breastfeeding | Small amounts of oral contraceptive steroids are excreted in breast milk, possibly decreasing milk quantity and quality. Use is generally not recommended during breastfeeding, especially in the early postpartum period. Alternative contraception methods are preferred. |
| Lactation Rating | L3 (Moderately Safe) — but use is generally avoided; may be used with caution if benefits outweigh risks. |
| Teratogenic Risk | Microgestin 1/20 (norethindrone acetate/ethinyl estradiol) is contraindicated in pregnancy. First trimester exposure has been associated with a small increase in risk of congenital anomalies, including cardiovascular and limb defects. Use in second and third trimesters may cause fetal harm, including female pseudohermaphroditism with high doses of progestins. |
| Fetal Monitoring | Monitor for signs of thromboembolic events, hypertension, and cholestasis. Assess fetal growth and development if inadvertent use during pregnancy. No specific fetal monitoring is routinely required, but if used inadvertently, consider ultrasound for fetal anatomy. |
| Fertility Effects | Microgestin 1/20 is used for contraception; it suppresses ovulation and fertilization. After discontinuation, fertility typically returns promptly, but there may be a short delay in return of ovulatory cycles, especially with prolonged use. No permanent effects on fertility. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events (e.g., myocardial infarction, stroke, thromboembolism) from COC use. Risk increases with age (especially >35) and number of cigarettes smoked. Women >35 who smoke should not use COCs.
| Common Effects | Abdominal pain Nausea Abnormal vaginal bleeding Edema swelling Hair loss Abdominal bloating Headache Breast pain Vomiting Vaginal yeast infection |
| Serious Effects | Venous thromboembolism (VTE), Arterial thromboembolism (e.g., stroke, myocardial infarction), Hepatic adenoma or hepatocellular carcinoma, Gallbladder disease, Hypertension, Cerebral hemorrhage, Optic neuritis or retinal thrombosis |
Thrombophlebitis or thromboembolic disordersCerebrovascular or coronary artery diseaseKnown or suspected breast carcinomaEstrogen-dependent neoplasiaUndiagnosed abnormal genital bleedingPregnancyHepatic adenoma or carcinomaKnown liver disease or impaired liver function
| Precautions | Risk of thromboembolic disorders (e.g., DVT, PE, stroke, MI) - discontinue if symptoms occur, Increased risk of myocardial infarction, especially in smokers ≥35, Elevated blood pressure - monitor periodic BP, Gallbladder disease risk, Hepatic neoplasia risk (benign/malignant) - discontinue if jaundice develops, May worsen diabetes, hyperlipidemia, or migraines, Women with history of depression should be monitored, Retinal thrombosis - discontinue if visual symptoms occur, Increased risk of pancreatitis in women with hypertriglyceridemia, Possible increase in breast cancer risk - individual risk/benefit assessment |
| Food/Dietary | No specific food restrictions; however, grapefruit juice may increase estrogen levels and is best avoided. High-fat meals may delay absorption but not clinically significant. |
| Clinical Pearls | Initiate on first day of menstrual period or first Sunday after onset; no need for back-up contraception if started within first 5 days. Missed pill protocols: if 1 pill missed, take as soon as remembered; if 2+ pills missed, take last missed pill, use back-up for 7 days. May reduce menstrual cramps and acne. Contraindicated in smokers over 35 and those with history of DVT or migraine with aura. |
| Patient Advice | Take one tablet daily at the same time to maintain steady hormone levels. · If you miss a pill, refer to the package insert for instructions; use backup contraception if needed. · Common side effects include nausea, breast tenderness, and breakthrough bleeding, which usually improve after 2-3 cycles. · This medication does not protect against HIV or other STDs; use condoms for protection. · Notify your provider if you experience severe abdominal pain, chest pain, shortness of breath, or vision changes. |
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