LARIN 24 FE
Clinical safety rating: caution
Comprehensive 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. |
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 | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for LARIN 24 FE (LARIN 24 FE).
| Breastfeeding | Combined hormonal contraceptives like LARIN 24 FE are generally not recommended during breastfeeding due to potential suppression of milk production and excretion of small amounts of hormones into breast milk. The M/P ratio is not well established; estrogens and progestins are present in milk at low concentrations. Use in lactating women should be avoided, especially in early postpartum period. Alternative contraception methods are preferred. |
| 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. |
■ 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.
| Serious Effects |
["Known or suspected pregnancy","Current or past history of thrombophlebitis or thromboembolic disorders","Cerebrovascular or coronary artery disease","Known or suspected breast cancer","Endometrial cancer or other estrogen-dependent neoplasia","Undiagnosed abnormal genital bleeding","Cholestatic jaundice of pregnancy or jaundice with prior oral contraceptive use","Hepatic adenomas or carcinomas","Known or suspected hypersensitivity to any component of the product","Heavy smoking (>15 cigarettes/day) and age >35 years"]
| 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)"] |
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| 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. |