Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ESTROSTEP 21 vs A.P.L.
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Estrostep 21 is a combination oral contraceptive containing ethinyl estradiol and norethindrone acetate. It works primarily by suppressing gonadotropin-releasing hormone (Gn RH) from the hypothalamus, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion from the pituitary, thereby inhibiting ovulation. Additionally, it thickens cervical mucus to impede sperm penetration and alters the endometrium to reduce implantation likelihood.
A. P. L. (Chorionic Gonadotropin) acts as a luteinizing hormone (LH) agonist, binding to LH receptors in the gonads to stimulate testosterone production in males and ovulation in females.
Prevention of pregnancy,Treatment of moderate acne vulgaris in females >= 15 years of age who have achieved menarche, are not pregnant, and desire oral contraception
Induction of ovulation in anovulatory infertile women,Treatment of hypogonadism and cryptorchidism in males,Off-label: Assisted reproductive technology (ART) protocols
One tablet orally once daily for 21 days, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg.
500-1000 mg every 4-6 hours, not to exceed 3000 mg/day in adults.
Ethinyl estradiol: 13-27 hours (terminal); norethindrone acetate: 5-14 hours (terminal). Steady-state achieved within 3-5 days.
Terminal elimination half-life: 2.5–3.5 hours (elimination phase); clinical context: requires repeated dosing for sustained effect.
Ethinyl estradiol is metabolized primarily via CYP3A4 and undergoes glucuronidation and sulfation. Norethindrone acetate is deacetylated to norethindrone, which is metabolized by CYP3A4 and other CYP enzymes, and undergoes reduction and glucuronidation.
Primarily via glucuronidation (60%) and sulfation (35%) in the liver, with a minor portion (5%) via CYP2E1 oxidation to the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI), which is normally detoxified by glutathione.
Biliary/fecal (40-50% as metabolites) and renal (30-40% as glucuronide and sulfate conjugates)
Renal: 10% unchanged; hepatic metabolism to inactive metabolites excreted in urine and feces (90% combined).
Ethinyl estradiol: 97-98% bound to albumin; norethindrone: 95-97% bound to albumin and SHBG.
80–90% bound to sex hormone-binding globulin (SHBG) and albumin.
Ethinyl estradiol: 2.5-4.5 L/kg; norethindrone: 3.5-5.5 L/kg. Indicates extensive tissue distribution.
0.5–0.9 L/kg, indicating moderate tissue distribution (primarily gonads and liver).
Ethinyl estradiol: 38-48% (oral, first-pass metabolism); norethindrone acetate: 50-70% (oral, deacetylation to norethindrone).
IM: 100%; Subcutaneous: ~80% (relative to IM); Oral: <5% (not clinically used).
No dose adjustment required for mild to moderate renal impairment. Contraindicated in severe renal impairment or acute renal failure.
No specific adjustment required for mild to moderate renal impairment. In severe renal impairment (Cr Cl < 10 m L/min), extend dosing interval to every 8 hours.
Contraindicated in acute hepatitis, severe cirrhosis, benign or malignant liver tumors, or Child-Pugh class C cirrhosis. Use with caution in Child-Pugh class A or B; consider alternative therapy.
Caution in severe hepatic impairment; consider dose reduction or extended interval. Avoid use in active liver disease.
Not indicated for use before menarche. Post-menarche: same dosing as adults; use lowest effective dose for shortest duration.
Weight-based: 10-15 mg/kg every 4-6 hours, not to exceed 5 doses per day or 75 mg/kg/day.
Not indicated for postmenopausal women; no established dosing in elderly. Consider alternative therapies as necessary.
No specific dose adjustment, but consider renal and hepatic function and avoid exceeding 3000 mg/day.
Cigarette smoking increases the risk of serious cardiovascular events from oral contraceptive use. This risk increases with age (especially in women > 35 years) and with the number of cigarettes smoked. Women who use oral contraceptives should be strongly advised not to smoke.
No black box warning.
Increased risk of thromboembolic disorders (e.g., venous thromboembolism, stroke, myocardial infarction), especially in smokers and women over 35,Hepatic neoplasia (benign and malignant) reported,Hypertension and gallbladder disease,Carbohydrate and lipid effects; monitor in diabetic patients,Ocular lesions (e.g., retinal thrombosis); discontinue if unexplained vision loss or proptosis occurs,Hereditary angioedema exacerbation,Chloasma; avoid sun exposure,Menstrual irregularities (e.g., breakthrough bleeding, amenorrhea),Depression; discontinue if severe
May cause fluid retention, ovarian hyperstimulation syndrome (OHSS) in females,Increased risk of thromboembolic events,Precocious puberty in males,Not for use in prepubertal children unless for cryptorchidism
Thrombophlebitis, thromboembolic disorders, or history thereof (e.g., deep vein thrombosis, pulmonary embolism),Cerebrovascular disease (e.g., stroke, TIA),Coronary artery disease (e.g., myocardial infarction, angina),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,Benign or malignant liver tumors,Known or suspected pregnancy,Hypersensitivity to any component,Smoking in women over 35 years of age
Hypersensitivity to chorionic gonadotropin or any component,Precocious puberty (in males),Prostatic carcinoma or other androgen-dependent neoplasms,Ovarian cyst or enlargement not due to polycystic ovary syndrome
No specific food interactions. Grapefruit juice may increase estrogen exposure (mild effect). Maintain consistent timing with meals to reduce nausea if needed. Avoid alcohol if liver function is compromised.
No known food interactions. Avoid alcohol during treatment.
Estrostep 21 (norethindrone acetate/ethinyl estradiol) is contraindicated in pregnancy. First trimester: increased risk of cardiovascular malformations, limb reduction defects, and neural tube defects. Second and third trimesters: associated with fetal genital abnormalities, feminization of male fetuses, and potential long-term reproductive effects. Use in early pregnancy for emergency contraception is not recommended due to potential risks.
A. P. L. (chorionic gonadotropin) is not expected to increase the risk of congenital anomalies when used in early pregnancy. However, use in the first trimester is generally avoided unless indicated for specific conditions. Data are limited; no increased fetal risk reported in inadvertent exposures. Second and third trimester use is not associated with teratogenicity but may increase risk of multiple gestation (if used for ovulation induction).
Estrostep 21 is excreted in breast milk in small amounts; ethinyl estradiol M/P ratio approximately 0.1; norethindrone M/P ratio ~0.5. May reduce milk production and quality, especially in early lactation. Use generally avoided during breastfeeding; consider progestin-only alternatives.
Chorionic gonadotropin is not detected in breast milk following maternal administration. M/P ratio not established. Considered compatible with breastfeeding; no adverse effects on infant reported. Use with caution if high doses are administered.
Estrostep 21 is contraindicated in pregnancy; no dose adjustments recommended as use is avoided. Pharmacokinetic changes during pregnancy (increased hepatic metabolism, volume of distribution) would require dose adjustment if used, but due to risks, alternative therapy is indicated.
No pharmacokinetic studies in pregnancy. Dose adjustments are not typically required during pregnancy for standard indications. For ovulation induction, dosing is based on follicular development. In first trimester for luteal support, standard doses are used. No evidence of altered clearance or need for dose changes due to pregnancy.
ESTROSTEP 21 is a monophasic oral contraceptive containing norethindrone acetate and ethinyl estradiol. Due to its low estrogen dose (20 mcg), it may be associated with more breakthrough bleeding compared to higher-dose pills. It is indicated for contraception and may be used for acne treatment. The 21-day regimen requires a 7-day hormone-free interval. Counsel patients that smoking increases the risk of serious cardiovascular adverse effects; avoid in women over 35 who smoke.
A. P. L. (chorionic gonadotropin) is used to trigger ovulation in assisted reproductive technology. Administer when follicles are mature (≥18 mm). Risk of ovarian hyperstimulation syndrome (OHSS) increases with higher doses. Monitor for abdominal pain, distension, and weight gain. Use caution in patients with prior thromboembolism.
Take one tablet daily at the same time each day for 21 days, then no pills for 7 days.,If you miss a dose, follow the package instructions; use backup contraception if missed more than one tablet.,Do not smoke while taking this medication; smoking increases risk of blood clots, stroke, and heart attack, especially if over 35.,Common side effects include spotting, nausea, breast tenderness, and headache; these often improve after a few cycles.,Seek emergency care if you have signs of a blood clot: sudden leg pain, chest pain, shortness of breath, or vision changes.,This medication does not protect against HIV or other sexually transmitted infections.,Take missed pills as soon as remembered; do not take more than two tablets in one day.
This medication is given as an injection exactly as prescribed to trigger ovulation.,A single dose is usually sufficient; follow your doctor's timing instructions closely.,Common side effects include headache, fatigue, and injection site reactions.,Seek immediate medical help if you experience severe pelvic pain, nausea, vomiting, or sudden weight gain (signs of OHSS).,Report symptoms of blood clots: leg pain, chest pain, or shortness of breath.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ESTROSTEP 21 vs A.P.L., answered by our medical review team.
ESTROSTEP 21 is a Combined Oral Contraceptive that works by Estrostep 21 is a combination oral contraceptive containing ethinyl estradiol and norethindrone acetate. It works primarily by suppressing gonadotropin-releasing hormone (Gn RH) from the hypothalamus, reducing luteinizing hormone (LH) and follicle-stimulating hormone (FSH) secretion from the pituitary, thereby inhibiting ovulation. Additionally, it thickens cervical mucus to impede sperm penetration and alters the endometrium to reduce implantation likelihood.. A.P.L. is a Gonadotropin that works by A. P. L. (Chorionic Gonadotropin) acts as a luteinizing hormone (LH) agonist, binding to LH receptors in the gonads to stimulate testosterone production in males and ovulation in females.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ESTROSTEP 21 and A.P.L. depend on the specific clinical indication. These are agents from distinct pharmacological classes and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ESTROSTEP 21 is: One tablet orally once daily for 21 days, each tablet contains norethindrone acetate 1 mg and ethinyl estradiol 20 mcg.. The standard adult dose of A.P.L. is: 500-1000 mg every 4-6 hours, not to exceed 3000 mg/day in adults.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ESTROSTEP 21 and A.P.L. in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ESTROSTEP 21 is classified as Category C. Estrostep 21 (norethindrone acetate/ethinyl estradiol) is contraindicated in pregnancy. First trimester: increased risk of cardiovascular malformations, limb reduction defects, and. A.P.L. is classified as Category C. A.P.L. (chorionic gonadotropin) is not expected to increase the risk of congenital anomalies when used in early pregnancy. However, use in the first trimester is generally avoided . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.