KELNOR 1/50
Clinical safety rating: caution
Comprehensive 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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for KELNOR 1/50 (KELNOR 1/50).
| Breastfeeding | Norethindrone (progestin) and mestranol (estrogen) are excreted into breast milk. M/P ratio for norethindrone is approximately 0.5–0.6. Mestranol is metabolized to ethinyl estradiol, with limited data on excretion. Breastfeeding is generally not recommended during use; may reduce milk production and quality. Avoid use in breastfeeding women due to potential adverse effects on infant. |
| 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. |
■ 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.
| Serious Effects |
["Thrombophlebitis or thromboembolic disorders (current or history)","Cerebrovascular or coronary artery disease (current or history)","Known or suspected carcinoma of the breast or endometrium","Undiagnosed abnormal genital bleeding","Pregnancy or suspected pregnancy","Jaundice or hepatocellular disease with cholestasis (current or history)","Heavy smoking (≥15 cigarettes/day) in women >35 years","Hepatic adenoma or carcinoma","Known or suspected estrogen-dependent neoplasia"]
| 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"] |
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| 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. |