NORLESTRIN 21 2.5/50
Clinical safety rating
cautionComprehensive clinical and safety monograph for NORLESTRIN 21 2.5/50 (NORLESTRIN 21 2.5/50).
Combination oral contraceptive containing an estrogen (ethinyl estradiol) and a progestin (norethindrone acetate). Inhibits ovulation by suppressing gonadotropin release. Increases viscosity of cervical mucus, impeding sperm penetration, and alters endometrial receptivity.
| Metabolism | Ethinyl estradiol undergoes first-pass metabolism in the liver via CYP3A4; also subject to conjugation (sulfation and glucuronidation). Norethindrone acetate is rapidly hydrolyzed to norethindrone, which is metabolized primarily via reduction and conjugation, with CYP3A4 involvement. |
| Excretion | Renal: 50-60% as metabolites (glucuronide and sulfate conjugates of norethindrone and ethinyl estradiol); fecal: 30-40% via biliary elimination; <1% unchanged. |
| Half-life | Norethindrone: 8 hours (terminal); Ethinyl estradiol: 13 hours (terminal). Clinical context: Steady-state achieved after 3-5 days; dosing interval based on once-daily administration. |
| Protein binding | Norethindrone: 61% bound to albumin and SHBG; Ethinyl estradiol: 97-98% bound to albumin. |
| Volume of Distribution | Norethindrone: 2.7 L/kg (extensive tissue distribution and binding); Ethinyl estradiol: 3.2 L/kg (indicating distribution beyond total body water). |
| Bioavailability | Oral: Norethindrone 64%, Ethinyl estradiol 45% (first-pass metabolism). |
| Onset of Action | Oral: Ovulation suppression begins within 24 hours; full contraceptive effect after 7 days of continuous dosing. |
| Duration of Action | Single dose: 24 hours (maintains contraceptive effect). Clinical notes: Withdrawal bleeding occurs 2-3 days after last active pill; return to fertility may be delayed up to 3 months. |
| Molecular Weight | 340.46 |
One tablet orally once daily for 21 days, followed by 7 days off, then repeat.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment required in renal impairment; use with caution if severe impairment. |
| Liver impairment | Contraindicated in acute hepatic disease or severe cirrhosis (Child-Pugh C). In mild to moderate impairment (Child-Pugh A or B), use with caution and monitor; no dose adjustment guidelines established. |
| Pediatric use | Not indicated for use before menarche. For post-menarche adolescents, follow adult dosing. |
| Geriatric use | Not indicated for use in postmenopausal women due to risk-benefit profile; consider alternative therapies. |
| 1st trimester | Contraindicated: Increased risk of cardiovascular events and thromboembolism, associated with fetal development abnormalities (limb defects, cardiac anomalies) and potential for masculinization of female fetuses due to androgenic progestin (norethindrone). |
| 2nd trimester | Contraindicated: Risk of masculinization of female fetuses continues; potential for adverse effects on fetal growth and development due to hormonal exposure. |
| 3rd trimester | Contraindicated: Risk of masculinization of female fetuses persists; possible association with preterm birth and low birth weight. |
Clinical note
Comprehensive clinical and safety monograph for NORLESTRIN 21 2.5/50 (NORLESTRIN 21 2.5/50).
| Placental transfer | Both components cross the placenta. Norethindrone and ethinyl estradiol are detectable in fetal tissues and amniotic fluid. Significant transfer occurs, with potential for fetal hormonal effects. |
| Breastfeeding | Norethindrone and ethinyl estradiol are excreted in human milk in low amounts. Estrogens may reduce milk production and composition, especially in early postpartum. Use only if clearly needed and weigh benefits against potential risks to the infant, such as jaundice and breast enlargement. |
| Lactation Rating | L3 (Moderately Safe) - Limited data; potential for adverse effects in the infant, but generally compatible with breastfeeding if benefits outweigh risks. Use caution. |
| Teratogenic Risk | First trimester: No increased risk of major birth defects based on large observational studies. Second and third trimesters: Avoid use due to association with female genital tract anomalies (e.g., vaginal adenosis, cervical erosion) and potential for hormonal effects on fetal development. Postnatal: Possible delayed bone growth and transient withdrawal bleeding in neonates. |
| Fetal Monitoring | Monitor for pregnancy status if pregnancy is suspected. Inadvertent use in first trimester: No specific monitoring required beyond routine prenatal care. Use in later pregnancy: Fetal ultrasonography to assess genital tract development and growth parameters. Assess neonatal bone health if exposure near term. |
| Fertility Effects | Not indicated during pregnancy. As a contraceptive, it prevents pregnancy. After discontinuation, return to fertility is typically prompt; no evidence of permanent fertility impairment. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events from combination oral contraceptive use. Risk increases with age (especially >35 years) and with number of cigarettes smoked. Women who use combination hormonal contraceptives should be strongly advised not to smoke.
| Serious Effects |
Thrombophlebitis or thromboembolic disordersHistory of deep-vein thrombophlebitis or thromboembolic disordersCerebrovascular or coronary artery diseaseKnown or suspected carcinoma of the breastCarcinoma of the endometrium or other estrogen-dependent neoplasiaUndiagnosed abnormal genital bleedingCholestatic jaundice of pregnancy or jaundice with prior pill useHepatic adenoma or carcinomaKnown or suspected pregnancy
| Precautions | Thromboembolic disorders (venous and arterial), Cardiovascular disease (myocardial infarction, stroke), Hepatic neoplasia (benign and malignant), Carcinoma of the breast and reproductive organs, Ocular lesions (retinal thrombosis), Gallbladder disease, Carbohydrate and lipid metabolism effects, Elevated blood pressure, Headache/migraine, Irregular bleeding, Depression |
| Food/Dietary | No specific food interactions are clinically significant. Grapefruit juice may slightly increase ethinyl estradiol levels but not considered clinically relevant. Avoid excessive alcohol consumption as it may increase liver enzyme activity and reduce efficacy. Maintain consistent dietary habits for optimal absorption. |
| Clinical Pearls | NORLESTRIN 21 2.5/50 contains norethindrone acetate 2.5 mg and ethinyl estradiol 50 mcg. It is a high-estrogen-dose combination oral contraceptive. Use with caution in patients with cardiovascular risk factors due to increased thromboembolic risk. The 50 mcg EE dose may cause more estrogenic side effects (nausea, breast tenderness) than lower-dose pills. It is also used for endometriosis and dysmenorrhea. Missed pill management: if one pill is missed, take as soon as remembered; if two or more missed, use backup contraception. |
| Patient Advice | Take one tablet daily at the same time for 21 consecutive days, then none for 7 days (placebo week only if included in pack). · Do not skip doses; if you miss a pill, follow the instructions in the patient insert. · This medication does not protect against HIV or other sexually transmitted infections. · Smoking increases the risk of serious cardiovascular side effects; avoid smoking while taking this medication. · Common side effects include nausea, breast tenderness, headache, and breakthrough bleeding; these may improve with continued use. · Seek emergency care if you experience signs of a blood clot: sudden chest pain, shortness of breath, leg pain or swelling, or sudden severe headache. · Inform your healthcare provider about all medications, including herbal supplements (e.g., St. John's wort may reduce effectiveness). |
Loading safety data…