IMPLANON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for IMPLANON (IMPLANON).
Etonogestrel, a progestin, binds to progesterone and androgen receptors, suppressing gonadotropin release (FSH, LH) and preventing ovulation. It also increases cervical mucus viscosity, impeding sperm penetration, and alters endometrial morphology.
| Metabolism | Hepatic metabolism primarily via CYP3A4 isoenzyme to hydroxylated metabolites, which undergo conjugation and renal excretion. Etonogestrel is extensively protein-bound (95-99%). |
| Excretion | Metabolites primarily excreted in urine (approximately 50%) and feces (30-35%) |
| Half-life | Terminal elimination half-life is approximately 25-30 hours; significant interindividual variability |
| Protein binding | >99% bound, primarily to sex hormone-binding globulin (SHBG) and albumin |
| Volume of Distribution | Approximately 1.2 L/kg, indicating extensive tissue distribution |
| Bioavailability | 100% (implant) |
| Onset of Action | Contraceptive effect achieved within 24 hours if implanted during first 5 days of menstrual cycle; otherwise, within 7 days |
| Duration of Action | Contraceptive efficacy for up to 3 years; removal required to restore fertility |
Insert 1 rod (68 mg etonogestrel) subdermally in the inner upper arm; replacement every 3 years.
| Dosage form | IMPLANT |
| Renal impairment | No dose adjustment required for any degree of renal impairment. |
| Liver impairment | Contraindicated in severe hepatic disease (Child-Pugh C). No formal adjustment for mild to moderate impairment; use with caution. |
| Pediatric use | Same as adult dosing once menstruation has begun; insert 1 rod subdermally, replace every 3 years. |
| Geriatric use | Not indicated for use after menopause; no specific geriatric studies. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for IMPLANON (IMPLANON).
| Breastfeeding | Etonogestrel is excreted in breast milk in small amounts; M/P ratio approximately 0.44. No adverse effects reported in nursing infants. Theoretical risk of progestogenic effects. Endogenous milk production may be reduced. Use with caution in breastfeeding women, especially in first 6 weeks postpartum. |
| Teratogenic Risk | FDA Pregnancy Category X. No adequate studies in pregnant women; etonogestrel is contraindicated in pregnant women due to association with fetal harm. Risk of congenital anomalies (e.g., cardiovascular, limb defects) in first trimester. No evidence of teratogenicity in second or third trimester from inadvertent exposure, but use contraindicated throughout pregnancy. |
■ FDA Black Box Warning
None
| Serious Effects |
Active or history of thromboembolic disorders, hepatic tumors (benign or malignant), known or suspected pregnancy, undiagnosed abnormal genital bleeding, hypersensitivity to etonogestrel, breast cancer or history thereof, and severe liver disease (current or past) with abnormal liver function tests.
| Precautions | Thrombotic disorders (venous or arterial thromboembolism), ectopic pregnancy, liver disease, menstrual irregularities, ovarian cysts, hypertension, thromboembolic risk factors, depression, and weight gain. |
Loading safety data…
| Fetal Monitoring | If inadvertent pregnancy occurs, monitor for ectopic pregnancy due to hormonal contraceptive use. No specific fetal monitoring required; confirm pregnancy with ultrasound and discontinue implant. Preconception counseling recommended. |
| Fertility Effects | Reversible infertility due to ovulation suppression. Normal fertility returns promptly upon removal; median time to ovulation 21–30 days. No long-term impairment of reproductive function. |