MICROGESTIN 1/20
Clinical safety rating: caution
Comprehensive 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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MICROGESTIN 1/20 (MICROGESTIN 1/20).
| Breastfeeding | Small amounts of contraceptive steroids have been identified in breast milk, with an estimated M/P ratio of approximately 0.3 for ethinyl estradiol. Norethindrone acetate is also excreted. Use may reduce milk production and composition, especially with early postpartum use. Generally not recommended during breastfeeding due to potential effects on the infant. |
| 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. |
■ 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 |
["Thrombophlebitis or thromboembolic disorders (current or history)","Cerebrovascular or coronary artery disease (current or history)","Known or suspected breast carcinoma","Undiagnosed abnormal genital bleeding","Known or suspected pregnancy","Hepatic adenoma or carcinoma (current or history)","Jaundice or liver disease with impaired function (active)","Hypersensitivity to any component","Age >35 and smokes"]
| 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"] |
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| 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. |