KELNOR 1/50
Clinical safety rating
cautionComprehensive clinical and safety monograph for KELNOR 1/50 (KELNOR 1/50).
Combination hormonal contraceptive: ethinyl estradiol provides estrogenic activity, suppressing gonadotropin release; norethindrone acetate provides progestational activity, inhibiting ovulation and causing cervical mucus thickening.
| Metabolism | Hepatic via CYP3A4 (ethinyl estradiol) and various reductases (norethindrone acetate); undergoes extensive first-pass metabolism. |
| Excretion | Renal: ~50% (as metabolites, primarily ethinyl estradiol glucuronide and sulfate conjugates; norethindrone metabolites). Fecal: ~35% (biliary excretion of conjugates followed by hydrolysis and elimination). Unchanged drug: <5%. |
| Half-life | Ethinyl estradiol: biphasic, terminal half-life 13-27 hours (mean ~17 h); norethindrone: monoexponential, half-life 5-14 hours (mean ~8 h). Steady-state achieved after 3-5 days. Accumulation may occur in patients with hepatic impairment. |
| Protein binding | Ethinyl estradiol: ~97% bound to albumin (specific binding to SHBG). Norethindrone: ~92% bound to albumin and SHBG. |
| Volume of Distribution | Ethinyl estradiol: 2-4 L/kg (distributes widely into body tissues, including breast, liver, adipose, and reproductive organs). Norethindrone: 3-5 L/kg (extensive distribution). |
| Bioavailability | Oral: Ethinyl estradiol ~40-45% (due to first-pass metabolism in gut wall and liver); norethindrone ~50-60% (presystemic metabolism). |
| Onset of Action | Oral: contraceptive effect requires consistent dosing over one cycle; maximum plasma levels reached 1-2 hours post-dose, but suppression of ovulation takes several days to establish. |
| Duration of Action | Duration of contraceptive effect: 24 hours (maintained by daily dosing). After discontinuation, ovulatory function returns within 2-4 weeks. Duration of plasma exposure: ethinyl estradiol ~24h, norethindrone ~12h. |
| Molecular Weight | Norethindrone: 298.42 Da; Ethinyl estradiol: 296.40 Da. (Combination product) |
| Action Class | Estrogen-progestin combination oral contraceptive |
One tablet (norethindrone 1 mg/ethinyl estradiol 50 mcg) orally once daily, taken at the same time each day for 21 days, followed by 7 days of placebo.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. For severe renal impairment (GFR <30 mL/min) or end-stage renal disease, use is generally not recommended due to potential fluid retention and hyperkalemia; consider alternative contraception. |
| Liver impairment | Contraindicated in acute hepatic disease or decompensated cirrhosis (Child-Pugh class B or C). For mild hepatic impairment (Child-Pugh class A), no dose adjustment; use with caution and monitor liver function. |
| Pediatric use | Not indicated for use in pediatric patients before menarche. For adolescent females post-menarche, same dosing as adults: one tablet orally daily per 21-day cycle. |
| Geriatric use | Not indicated for use in postmenopausal women. No specific geriatric dose adjustments; evaluate cardiovascular and thromboembolic risks prior to use in women over age 35 who smoke or have risk factors. |
| 1st trimester | Use is not recommended during the first trimester due to the risk of congenital malformations, particularly cardiovascular and neural tube defects, associated with hormonal agents. |
| 2nd trimester | Use is generally contraindicated because of possible adverse effects on fetal development, including potential virilization of female fetuses and other teratogenic effects. |
| 3rd trimester | Use is contraindicated as progestins can cause androgenic effects on the fetus and may lead to developmental abnormalities. |
Clinical note
Comprehensive clinical and safety monograph for KELNOR 1/50 (KELNOR 1/50).
| Placental transfer | Both norethindrone and ethinyl estradiol cross the placenta. Norethindrone reaches fetal plasma concentrations approximately 10-50% of maternal levels, while ethinyl estradiol shows substantial placental transfer with fetal levels about 1-5% of maternal levels. |
| Breastfeeding | Norethindrone and ethinyl estradiol are excreted in breast milk in small amounts. Use during lactation may reduce milk production and quality. The American Academy of Pediatrics considers progestin-only contraceptives compatible with breastfeeding; however, combined hormonal contraceptives are generally not recommended during the first six months postpartum. Use with caution and only if clearly needed. |
| Lactation Rating | L3 - Moderately Safe |
| Teratogenic Risk | FDA Pregnancy Category X. Contraindicated in pregnancy due to risk of fetal harm. First trimester: Use is associated with cardiovascular defects, limb reduction defects, and neural tube defects. Second and third trimesters: Risk of feminization of male fetus, urogenital anomalies, and other congenital anomalies. Postnatal effects include behavioral and intellectual developmental issues. |
| Fetal Monitoring | Not applicable in pregnancy due to contraindication. For women of reproductive potential: Conduct pregnancy test before initiation, and use effective contraception. Monitor for signs of pregnancy if accidental exposure occurs. If pregnancy is suspected, discontinue immediately and perform ultrasound for fetal evaluation. |
| Fertility Effects | Suppresses ovulation through gonadotropin inhibition. Normal fertility typically returns after discontinuation; however, menses may take 1–3 months to resume. No permanent impairment of fertility reported. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events from combination oral contraceptives. Risk increases with age and smoking severity (particularly in women >35 years). Women who use COCs should be strongly advised not to smoke.
| Common Effects | Nausea, Headache, Breast tenderness, Weight gain, Irregular uterine bleeding, Mood changes |
| Serious Effects | Venous thromboembolism (deep vein thrombosis, pulmonary embolism), Arterial thromboembolism (myocardial infarction, stroke), Hepatic adenoma or hepatocellular carcinoma, Hypertension, Gallbladder disease, Cerebral hemorrhage |
High risk of arterial or venous thrombotic diseases (e.g., current or history of deep vein thrombosis, pulmonary embolism, cerebrovascular disease, coronary artery disease)Known or suspected breast cancerKnown or suspected estrogen-dependent neoplasiaUndiagnosed abnormal genital bleedingBenign or malignant liver tumor or active liver disease (e.g., hepatitis, cirrhosis) with impaired liver functionKnown or suspected pregnancyHypersensitivity to any component of Kelnor 1/50Cigarette smoking in women over 35 years of ageUncontrolled hypertension (systolic ≥160 mmHg or diastolic ≥100 mmHg)Diabetes with vascular involvementMigraine with focal neurological symptoms (at any age) or migraine without aura in women over 35 years of ageMajor surgery with prolonged immobilization
| Precautions | Thromboembolic disorders (DVT, PE, stroke, MI), Vascular disease in diabetes mellitus, Hypertension, Gallbladder disease, Hepatic neoplasia, Carbohydrate/lipid effects, Ocular lesions (retinal thrombosis), Bleeding irregularities, Depression, Use in women with hereditary angioedema |
| Food/Dietary | No specific food interactions. Grapefruit juice may modestly increase ethinyl estradiol levels but not clinically significant. St. John's Wort and some herbal supplements may reduce efficacy; avoid concurrent use. Maintain consistent diet if taken with food to avoid gastrointestinal upset. |
| Clinical Pearls | KELNOR 1/50 is a combination oral contraceptive containing ethinyl estradiol 50 mcg and norethindrone 1 mg. It has a higher estrogen dose than modern low-dose pills, increasing thrombotic risk. Use with caution in smokers over 35, hypertensive patients, and those with migraines with aura. Consider alternative contraception in women with BMI > 30 due to possible efficacy reduction. Monitor for breakthrough bleeding and ensure no missed doses to maintain contraceptive efficacy. |
| Patient Advice | Take one pill daily at the same time each day, even if no intercourse occurs. · If you miss a pill, follow the package instructions; use backup contraception if needed. · Do not smoke while taking this medication, especially if over 35, due to increased risk of blood clots. · Report any signs of blood clots: sudden leg pain, chest pain, shortness of breath, or sudden severe headache. · This medication does not protect against HIV or other sexually transmitted infections. · Common side effects include nausea, headache, breast tenderness, and breakthrough bleeding in the first few months. |
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