LEVONEST
Clinical safety rating: caution
Comprehensive clinical and safety monograph for LEVONEST (LEVONEST).
Levonorgestrel is a synthetic progestin that inhibits ovulation by suppressing luteinizing hormone (LH) surge, alters cervical mucus to impede sperm penetration, and induces endometrial changes that inhibit implantation.
| Metabolism | Primarily hepatic via CYP3A4; undergoes reduction and conjugation; excreted in urine and feces. |
| Excretion | Renal excretion of conjugated metabolites accounts for approximately 60-80% of an administered dose; fecal elimination via bile accounts for 20-40%. |
| Half-life | The terminal elimination half-life is approximately 24-30 hours. This relatively long half-life supports once-daily dosing and allows for stable plasma concentrations within 5-7 days of continuous use. |
| Protein binding | Levonorgestrel is extensively bound to sex hormone-binding globulin (SHBG) and albumin; approximately 97-99% bound, with the free fraction being pharmacologically active. |
| Volume of Distribution | Apparent volume of distribution is about 1.8 L/kg, indicating extensive distribution into tissues beyond plasma water. |
| Bioavailability | Oral bioavailability is approximately 100% due to minimal first-pass metabolism; levonorgestrel is completely absorbed after oral administration. |
| Onset of Action | Oral administration: onset of contraceptive effect occurs within 24 hours if started on the first day of menstrual cycle. Withdrawal bleeding typically begins 2-7 days after completion of active tablets. |
| Duration of Action | Contraceptive efficacy persists for the duration of daily oral administration; after discontinuation, ovulation returns within 4-8 weeks. |
One tablet (levonorgestrel 1.5 mg) orally as a single dose within 72 hours of unprotected intercourse.
| Dosage form | TABLET |
| Renal impairment | No dosage adjustment required for any degree of renal impairment. |
| Liver impairment | Contraindicated in severe hepatic impairment (Child-Pugh class C). For mild to moderate impairment, no specific dose adjustment available; use with caution. |
| Pediatric use | Weight ≥ 75 kg: single dose of levonorgestrel 1.5 mg orally. Weight < 75 kg: single dose of 1.5 mg is also used, but efficacy may be reduced; consider alternative methods. |
| Geriatric use | Not indicated for postmenopausal women; no specific dose adjustment established for elderly. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for LEVONEST (LEVONEST).
| Breastfeeding | Levonorgestrel is excreted into breast milk in small amounts (estimated infant dose <0.1% of maternal dose). M/P ratio not established. No adverse effects reported in breastfed infants with short-term use. The WHO considers it compatible with breastfeeding. Caution with prolonged use may reduce milk supply. |
| Teratogenic Risk | LEVONEST (levonorgestrel) is associated with minimal teratogenic risk if inadvertently used during pregnancy. First trimester: No increased risk of major malformations based on epidemiologic data. Second/third trimester: No known adverse fetal effects from occasional use; no evidence of fetotoxicity or teratogenicity from clinical studies. However, as a progestin-only contraceptive, it is not indicated during pregnancy. |
■ FDA Black Box Warning
None.
| Serious Effects |
["Known or suspected pregnancy","Hypersensitivity to levonorgestrel or any component"]
| Precautions | ["Do not use as regular contraceptive if multiple doses are taken in one cycle","Ectopic pregnancy risk reduced but not eliminated","Menstrual irregularities","Rare cases of hepatic adenoma or thromboembolic events","Use with caution in patients with severe hepatic impairment or malabsorption syndromes"] |
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| Fetal Monitoring | No specific monitoring required for routine use. In pregnancy, if inadvertent exposure occurs, standard prenatal care is sufficient. For lactation, observe infant for unusual drowsiness or feeding difficulties. |
| Fertility Effects | Levonorgestrel does not impair future fertility. Fertility returns rapidly after discontinuation. No permanent negative impact on ovarian function or fecundity. |