MIRENA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for MIRENA (MIRENA).
Levonorgestrel, a progestin, suppresses endometrial proliferation via local progestogenic effects, leading to endometrial atrophy and reduced menstrual bleeding; also thickens cervical mucus and may inhibit ovulation.
| Metabolism | Primarily hepatic via CYP3A4; also reduced to inactive metabolites. Undergoes enterohepatic recirculation. |
| Excretion | Levonorgestrel is primarily excreted as metabolites in urine (40-45%) and feces (30-35%), with approximately 10% unchanged in urine. |
| Half-life | The terminal elimination half-life of levonorgestrel from Mirena is approximately 20 days (range 12-30 days) due to slow release from the intrauterine system, resulting in sustained systemic exposure. |
| Protein binding | Levonorgestrel is approximately 99% bound to proteins, primarily sex hormone-binding globulin (SHBG) and albumin. |
| Volume of Distribution | The apparent volume of distribution of levonorgestrel is approximately 1.8 L/kg, indicating extensive distribution into tissues. |
| Bioavailability | Systemic bioavailability of levonorgestrel from Mirena is approximately 100% as it is released directly into the uterine cavity, resulting in high local concentrations and low systemic levels. |
| Onset of Action | Contraceptive effect begins immediately upon insertion; therapeutic effect for heavy menstrual bleeding is typically noted within 3-6 months of insertion. |
| Duration of Action | Approved for up to 5 years for contraception and up to 5 years for heavy menstrual bleeding; however, contraceptive efficacy may persist for up to 7 years in some patients. |
Insert one Mirena intrauterine device (IUD) into the uterine cavity; releases 20 mcg levonorgestrel per day initially, decreasing over time; replace every 5 years.
| Dosage form | SYSTEM |
| Renal impairment | No dosage adjustment required for renal impairment. |
| Liver impairment | Contraindicated in acute liver disease or hepatic tumors (benign or malignant). No dose adjustment guidelines for Child-Pugh classification; use with caution in mild impairment. |
| Pediatric use | Approved for use in postmenarchal females under 18 years old; dosing per standard adult protocol (single IUD insertion). |
| Geriatric use | Not indicated for postmenopausal women; use after menopause is not recommended due to lack of efficacy and safety data. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for MIRENA (MIRENA).
| Breastfeeding | Levornogestrel is excreted in human milk with an M/P ratio of approximately 0.5 to 1.0. No adverse effects on breastfeeding or infant development have been reported at recommended doses, but caution is advised due to potential for neonatal jaundice and sex hormone-like effects. |
| Teratogenic Risk | FDA Pregnancy Category X. Use is contraindicated during pregnancy due to risk of ectopic pregnancy, fetal exposure to levonorgestrel, and potential for teratogenic effects including masculinization of female fetuses during second and third trimesters. |
■ FDA Black Box Warning
No FDA boxed warning.
| Common Effects | Irregular uterine bleeding Ovarian cysts Pelvic pain Dizziness |
| Serious Effects |
["Pregnancy or suspected pregnancy","Postpartum endometritis or infected abortion (within 3 months)","Known or suspected breast cancer","Acute liver disease or liver tumors","Uterine anomaly distorting cavity","Active pelvic inflammatory disease or recurrent PID","Unexplained abnormal uterine bleeding","Allergy to levonorgestrel or any component"]
| Precautions | ["Risk of ectopic pregnancy","Pelvic inflammatory disease (PID)","Embedment or perforation of uterine wall","Expulsion","Ovarian cysts","Breast cancer risk (unknown)","Use in patients with acute hepatitis or liver tumors"] |
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| Fetal Monitoring |
| Monitor for signs of ectopic pregnancy, especially in women with history of pelvic inflammatory disease or tubal surgery. Perform pregnancy test if pregnancy is suspected. Ultrasound may be required to confirm intrauterine placement if pregnancy occurs. |
| Fertility Effects | Mirena provides effective contraception and is reversible upon removal. After removal, return to fertility is rapid, with most women ovulating within the first month. Long-term use does not impair future fertility. |