LARIN 24 FE
Clinical safety rating
cautionComprehensive clinical and safety monograph for LARIN 24 FE (LARIN 24 FE).
Combination oral contraceptive containing ethinyl estradiol (estrogen) and norethindrone (progestin). Inhibits ovulation by suppressing gonadotropin release (FSH and LH). Increases cervical mucus viscosity, impeding sperm penetration, and alters endometrial structure, reducing implantation likelihood.
| Metabolism | Ethinyl estradiol: CYP3A4; undergoes first-pass metabolism in liver and gut wall, sulfation and glucuronidation. Norethindrone: primarily hepatic reduction and conjugation; metabolized via CYP3A4 and CYP2C9. |
| Excretion | Ethinyl estradiol: 40% renal, 60% fecal; norethindrone: 40% renal, 60% fecal. |
| Half-life | Ethinyl estradiol: ~13 hours (range 7–20); norethindrone: ~8 hours (range 5–14). Half-life supports once-daily dosing; steady state achieved within 5–7 days. |
| Protein binding | Ethinyl estradiol: 98% bound to albumin and SHBG; norethindrone: 93% bound to albumin and SHBG. |
| Volume of Distribution | Ethinyl estradiol: 2.3–4.0 L/kg; norethindrone: 3.0–4.5 L/kg. Indicates extensive tissue distribution. |
| Bioavailability | Ethinyl estradiol: ~45% (range 38–48%); norethindrone: ~65% (range 60–70%). First-pass metabolism reduces oral bioavailability. |
| Onset of Action | Oral: Suppression of ovulation occurs within 7 days of continuous use if started on first day of menstrual cycle; immediate contraceptive effect if started on day 1 of menses. |
| Duration of Action | Oral: Contraceptive protection lasts as long as daily dosing is maintained; missing pills increases pregnancy risk. Withdrawal bleeding typically occurs during placebo week. |
| Molecular Weight | Ethinyl estradiol: 296.41 Da; Norethindrone: 298.42 Da (combined product). |
| Action Class | Combination Oral Contraceptive (Estrogen-Progestin) |
One tablet (20 mcg ethinyl estradiol / 1 mg norethindrone acetate) orally once daily for 24 days, followed by 1 iron-containing placebo tablet (75 mg ferrous fumarate) orally once daily for 4 days.
| Dosage form | TABLET |
| Renal impairment | No specific dose adjustment recommended; use with caution in patients with renal impairment. No GFR-based guidelines established. |
| Liver impairment | Contraindicated in patients with hepatic adenomas, acute hepatitis, or decompensated cirrhosis (Child-Pugh class B or C). No dose adjustment recommended in mild hepatic impairment (Child-Pugh class A) but use with caution. |
| Pediatric use | Safety and efficacy established for use after menarche; dose same as adult: one active tablet daily for 24 days then one placebo tablet daily for 4 days. No weight-based dosing. |
| Geriatric use | Not indicated for postmenopausal women; no specific dose adjustment recommended, but consider increased risk of thromboembolic events and cardiovascular disease in older women. |
| 1st trimester | Contraindicated: Use during pregnancy is associated with fetal harm, including cardiovascular and neural tube defects. Oral contraceptives should be discontinued if pregnancy occurs. |
| 2nd trimester | Contraindicated: Continued use in second trimester may increase risk of gestational hypertension, thromboembolic events, and adverse fetal outcomes. |
| 3rd trimester | Contraindicated: Use in third trimester may cause fetal withdrawal symptoms (jaundice, thrombocytopenia) and long-term metabolic effects. Avoid use. |
Clinical note
Comprehensive clinical and safety monograph for LARIN 24 FE (LARIN 24 FE).
| Placental transfer | Both ethinyl estradiol and norethindrone (the active components) cross the placenta readily. Studies confirm placental transfer with measurable fetal serum levels after maternal administration. |
| Breastfeeding | Combined hormonal contraceptives (estrogen and progestin) are generally not recommended during breastfeeding due to potential reduction in milk production and passage of hormones into breast milk. Larin 24 FE is best avoided; progestin-only methods are preferred. Use only if benefits outweigh risks, and monitor infant for jaundice or growth disturbances. |
| Lactation Rating | L4 - Possibly Hazardous |
| Teratogenic Risk | LARIN 24 FE (norethindrone/ethinyl estradiol) is contraindicated in pregnancy. First trimester exposure is not associated with major malformations based on epidemiological data, but there is a small increased risk of cardiovascular defects. Second and third trimester exposure may cause fetal harm, including feminization of male fetuses (mild hypospadias) and potential for other teratogenic effects. Use is not recommended during pregnancy. |
| Fetal Monitoring | If inadvertently used during pregnancy, monitor fetal growth and anatomy via ultrasound. No specific monitoring required if used as contraceptive; pregnancy test recommended before initiating therapy. Monitor for adverse effects such as thromboembolism, hypertension, and liver dysfunction. |
| Fertility Effects | LARIN 24 FE is used for contraception and effectively prevents fertility while used. Upon discontinuation, fertility typically returns quickly, though there may be a slight delay in return to ovulation. No permanent negative effects on fertility. |
■ FDA Black Box Warning
Cigarette smoking increases risk of serious cardiovascular events (e.g., stroke, myocardial infarction, thromboembolism) from oral contraceptive use. Risk increases with age and number of cigarettes smoked, particularly in women >35 years. Women who use oral contraceptives should be strongly advised not to smoke.
| Common Effects | Nausea, Headache, Breast tenderness, Weight changes, Irregular uterine bleeding, Mood changes, Acne |
| Serious Effects | Venous thromboembolism (VTE), Arterial thromboembolism (e.g., stroke, myocardial infarction), Hypertension, Hepatic adenoma or hepatocellular carcinoma, Gallbladder disease, Thrombotic thrombocytopenic purpura (TTP), Hemolytic uremic syndrome (HUS) |
Known or suspected pregnancyBreast cancer (current or history)Hepatic adenoma or hepatocellular carcinomaActive liver disease or impaired liver functionUndiagnosed abnormal uterine bleedingMigraine with aura age ≥35Hypertension (systolic ≥160 mmHg or diastolic ≥100 mmHg)Diabetes mellitus with vascular involvementDeep vein thrombosis or pulmonary embolism (current or history)Known thrombophilia (e.g., Factor V Leiden, antiphospholipid syndrome)Ischemic heart disease, cerebrovascular disease, or valvular heart disease with complicationsMajor surgery with prolonged immobilizationHypersensitivity to any componentSmoking age ≥35 and ≥15 cigarettes/day
| Precautions | Thromboembolic disorders (e.g., DVT, PE, stroke, MI), Cigarette smoking (increases cardiovascular risk), Hypertension, Gallbladder disease, Hepatic neoplasia (liver tumors), Carbohydrate/lipid metabolism effects (hyperglycemia, hypertriglyceridemia), Headache (including migraine), Uterine bleeding irregularities, Ocular lesions (e.g., retinal thrombosis), Depression, Pregnancy and postpartum use, Lactation (may reduce milk production) |
| Food/Dietary | No significant food interactions. Grapefruit juice may increase estrogen levels, but effect is minimal. Take with food if nausea occurs. |
| Clinical Pearls | LARIN 24 FE is a combined hormonal contraceptive containing ethinyl estradiol and norethindrone. It uses a 24/4 regimen with 24 active pills and 4 iron-containing placebo pills. The iron (ferrous fumarate) in placebo pills is not contraceptive and serves to reduce iron-deficiency anemia risk. Prescribe for contraception, acne, or menstrual disorders. Monitor for VTE risk, especially in smokers over 35. Consider drug interactions with CYP3A4 inducers (e.g., rifampin, certain anticonvulsants) which reduce efficacy. Breakthrough bleeding is common in the first 3 cycles. |
| Patient Advice | Take one pill daily at the same time; missing pills increases pregnancy risk. · Active pills are light blue; placebo pills are brown and contain iron. · Use backup contraception for the first 7 days if starting after Day 5 of menstrual cycle. · If you miss two or more active pills, take the last missed pill and use backup contraception for 7 days. · Smoking while on this pill increases risk of serious cardiovascular side effects; do not smoke. · Report signs of blood clots: sudden leg pain/swelling, chest pain, shortness of breath, or vision changes. · Iron in placebo pills helps prevent anemia but does not provide contraception. |
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