NORLESTRIN 21 2.5/50
Clinical safety rating: caution
Comprehensive 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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for NORLESTRIN 21 2.5/50 (NORLESTRIN 21 2.5/50).
| Breastfeeding | Norethindrone and ethinyl estradiol are excreted in breast milk in small amounts. M/P ratio not established. May reduce milk production and quality. Use is generally not recommended during breastfeeding unless necessity is clear. |
| 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. |
■ 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 |
["Known or suspected pregnancy","Current or history of thrombophlebitis or thromboembolic disorders","Cerebrovascular or coronary artery disease","Known or suspected breast cancer","Carcinoma of the endometrium or other estrogen-dependent neoplasia","Undiagnosed abnormal genital bleeding","Benign or malignant liver tumor (current or history)","Known or suspected liver disease (including impaired liver function)","Hypersensitivity to any component","Cholestatic jaundice of pregnancy or jaundice with prior pill use","Age >35 years and smoking ≥15 cigarettes per day"]
| 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"] |
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| 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. |