Etonogestrel

Introduction Overview

Generic Name

etonogestrel

Brand Name

Nexplanon

Dosage Form

Subdermal implant (flexible, thin plastic rod approximately 4 cm by 2 mm)

Drug Class

Contraceptives, Progestins

Pharmacokinetics

Absorption:
Etonogestrel from Nexplanon is absorbed systemically following subdermal implantation. The implant releases etonogestrel steadily and slowly over a three-year period, maintaining effective contraceptive plasma levels without significant peaks and troughs. Upon insertion, etonogestrel is released through diffusion from ethylene-vinyl acetate copolymer matrix into the surrounding tissue and then enters circulation. This controlled release avoids the first-pass hepatic metabolism seen with oral administration, allowing for consistent systemic hormone levels and high contraceptive efficacy.

Distribution:
After absorption, etonogestrel is widely distributed throughout the body. It binds extensively to plasma proteins, primarily sex hormone-binding globulin (SHBG) and albumin. The volume of distribution is moderate and reflects its lipophilicity allowing sequestration in fat and other tissues. The implant's subdermal placement offers a reservoir effect enabling steady plasma concentrations. Due to its high plasma protein binding, free etonogestrel levels remain low but sufficient for receptor-mediated activity. The implant enables a sustained release without large fluctuations in plasma levels, contributing to predictable pharmacodynamics.

Metabolism:
Etonogestrel is primarily metabolized in the liver by cytochrome P450 enzymes, especially CYP3A4 isoenzymes. It undergoes hydroxylation and reduction to form several inactive metabolites, which are then conjugated to glucuronides and sulfates. These metabolites lack progestational activity and are eventually excreted. Hepatic metabolism can be influenced by concurrent medications inducing or inhibiting CYP3A4, potentially altering plasma concentrations and contraceptive effectiveness. Research indicates enzyme-inducing drugs may reduce etonogestrel hormone levels, necessitating contraception counseling.

Elimination:
Elimination of etonogestrel and its metabolites is primarily via biliary excretion into feces and renal excretion through urine. The elimination half-life after implant removal is approximately 25 to 30 hours, with hormone levels falling below contraceptive thresholds within days to weeks. Upon implant removal, fertility typically returns rapidly, often within 7 to 14 days. The elimination profile supports the reversibility of contraception and rapid restoration of normal hormonal cycles post-removal. The implant’s controlled release maintains consistent hormone levels until removal, limiting abrupt exposure changes.

Dosage Forms

Available Dosage Forms:
Nexplanon is available exclusively as a single-use subdermal implant containing 68 mg of etonogestrel embedded in an ethylene-vinyl acetate copolymer matrix. The rod is flexible and radiopaque due to barium sulfate content, measuring approximately 4 cm in length and 2 mm in diameter for ease of insertion and localization via X-ray.

Dosages for Adults and Adolescents:
Nexplanon is indicated for use in women of reproductive age starting from 18 years and older. The implant delivers a continuous dose of etonogestrel sufficient to provide highly effective contraception for up to 3 years. The implant should be inserted subdermally in the inner side of the nondominant upper arm by a trained healthcare professional. No dose adjustment is necessary based on age or body weight, although efficacy may be slightly reduced in overweight women which should be considered during counseling.

Specific Patient Populations:
Nexplanon use is contraindicated in pregnant women, within 4 weeks postpartum in breastfeeding women, and within 3 weeks postpartum in non-breastfeeding women. Caution should be exercised in women with hepatic impairment or history of thromboembolic events. While not specifically dose adjusted, the implant is not recommended for use in women under 18 years. The implant's insertion timing relative to previous contraception or childbirth is critical to ensure immediate contraceptive efficacy; detailed guidelines exist to optimize timing after abortion, miscarriage, childbirth, and prior contraceptive use.

Mechanism Of Action

Nexplanon's active component, etonogestrel, is a synthetic progestin that exerts its primary contraceptive effect by modulating hypothalamic-pituitary-ovarian axis activity. It suppresses the mid-cycle surge of luteinizing hormone (LH) required for ovulation, effectively inhibiting the release of a mature ovum from the ovaries. This anovulatory effect is the primary mechanism preventing fertilization.

Beyond ovulation suppression, etonogestrel induces changes in cervical mucus composition, increasing its viscosity and reducing sperm penetration into the uterus. This physical barrier to sperm migration significantly decreases the likelihood of fertilization even if ovulation were to occur.

Etonogestrel also alters the endometrium by thinning the uterine lining (decidualization), which diminishes the likelihood of implantation of a fertilized egg. This local effect contributes to contraceptive efficacy by creating an inhospitable uterine environment for embryo development.

Comparatively, the mechanism aligns with other progestin-only contraceptives but benefits from the steady, low-dose release afforded by the implant, avoiding the plasma concentration fluctuations seen with oral progestins. Clinical studies have demonstrated near-complete ovulation suppression with Nexplanon over extended periods, supporting its high effectiveness with less systemic hormonal side effects. The implant's slow-release technology enables sustained receptor occupancy and prolonged pharmacodynamic effects critical for long-term contraception.

Pharmacological Actions

Inhibition of ovulation via suppression of luteinizing hormone (LH) surge
Thickening of cervical mucus to impede sperm penetration
Endometrial thinning leading to reduced implantation probability
Sustained systemic progestin effect from subdermal slow-release implant
Minimal estrogenic activity, reducing associated side effects
Reduced menstrual blood flow in some users due to endometrial effects
Potential alteration of tubal motility affecting fertilization
Progestin-induced suppression of follicular development
Non-oral delivery bypassing first-pass hepatic metabolism
Rapid reversibility of effects upon implant removal
Reduced risk of ovulatory bleeding and dysmenorrhea
Long-acting contraception up to three years post-insertion
Potential impact on breast tissue due to hormonal modulation
Influence on lipid profiles and coagulation parameters (minimal compared with combined contraceptives)
Hormonal modulation of hypothalamic-pituitary axis with feedback regulation

Therapeutic Or Clinical Uses

Long-term, reversible contraception in women of reproductive age
Prevention of pregnancy for up to three years
Contraception option for women seeking non-daily, non-oral birth control
Suitable for women with contraindications to estrogen-containing contraceptives
Contraceptive choice for breastfeeding women after 4 weeks postpartum
Alternative for women with gastrointestinal malabsorption issues precluding oral contraceptives
Method for women seeking discreet contraception
Option for patients with compliance concerns regarding daily contraceptive methods
Use in women intolerant or allergic to other hormonal contraceptives
Reduction of menstrual bleeding irregularities in select users
Contraception for women with contraindications to estrogen due to thromboembolism risk
Backup contraception when combined hormonal contraceptives are discontinued
Off-label use for menstrual regulation in some clinical situations
Fertility sparing contraceptive enabling immediate return to fertility post-removal
Effective contraceptive in overweight women albeit with reduced efficacy

Side Or Adverse Effects

Changes in menstrual bleeding patterns including irregular, prolonged, or absent periods
Mood swings and emotional lability
Weight gain reported by some users
Headache and migraine exacerbation
Acne flare or improvement depending on individual response
Depressed mood or symptoms of depression
Breast pain or tenderness
Vaginitis or vaginal irritation
Localized pain, swelling, bruising, or irritation at the insertion site
Numbness or tingling sensations near the implant site
Possibility of implant migration or bending causing discomfort
Nausea and dizziness in some patients
Rare cases of systemic allergic reactions including swelling or difficulty breathing
Risk of serious blood clots including deep vein thrombosis or pulmonary embolism
Potential formation of ovarian cysts, often asymptomatic

Precautions

Ensure negative pregnancy test prior to insertion
Avoid use in women with active liver disease or tumors
Use caution in women with history of thromboembolic disorders
Monitor for changes in menstrual bleeding and counsel regarding expected patterns
Advise immediate medical attention if signs of blood clots (leg pain, chest pain, shortness of breath) occur
Inform patients about possible implant migration or difficulty in palpation
Consider body weight when counseling on contraceptive effectiveness
Avoid insertion in women younger than 18 years old
Regular follow-up for implant location verification
Assessment of breast health, including regular self-exams and mammography screening
Advise patients to notify healthcare providers of implant presence during surgeries or imaging
Caution in patients on enzyme-inducing drugs that may lower hormone concentrations
Provide guidance on return to fertility following implant removal
Discuss potential mood-related side effects and monitor mental health
Advise smoking cessation to reduce vascular risks associated with progestin implants

Warnings

Do not use Nexplanon if pregnant or if less than 4 weeks postpartum while breastfeeding
Contraindicated within 3 weeks postpartum in non-breastfeeding women
Increased risk of serious blood clots, stroke, and heart attack especially in smokers, older women, and those with cardiovascular risk factors
Risk of ectopic pregnancy if contraceptive failure occurs; prompt evaluation needed if pregnancy suspected
Potential for implant bending or breaking, which may necessitate surgical removal
Possible development of ovarian cysts while implant in place
Not a protective method against sexually transmitted infections including HIV
Caution in women with a history or presence of hormone-sensitive malignancies such as breast cancer
Higher risk of adverse vascular events during the first year of use
Avoid smoking to reduce cardiovascular complication risks
Notify healthcare providers prior to surgeries or prolonged immobility due to increased thrombotic risk
Implant removal necessary prior to conception or if pregnancy confirmed
Report any signs of severe allergic reaction immediately
Potential liver-related adverse effects including rare tumors
Regular monitoring for unexpected vaginal bleeding is advised

Contraindication

Current or suspected pregnancy
Within 4 weeks postpartum in breastfeeding women
Within 3 weeks postpartum in non-breastfeeding women
Undiagnosed abnormal vaginal bleeding
Active liver disease or malignant liver tumors
History or presence of thromboembolic disorders (e.g., deep vein thrombosis, pulmonary embolism, stroke, myocardial infarction)
Known or suspected hormone-sensitive cancers such as breast, uterine, cervical, or vaginal cancer
Hypersensitivity to etonogestrel or any component of the implant
Major surgery necessitating prolonged immobilization without thromboprophylaxis
Severe uncontrolled hypertension
Migraine with aura or other significant cerebrovascular disease
Women under 18 years of age
Severe depression linked to hormonal contraceptive use
Presence of unexplained liver tumors
Patients who smoke and are over 35 years old (relative contraindication)
Concurrent use of certain enzyme-inducing medications reducing contraceptive efficacy without additional protection

Drug Interactions

Enzyme-inducing drugs such as carbamazepine reduce etonogestrel plasma levels, lowering contraceptive effectiveness
Phenytoin and phenobarbital may induce hepatic enzymes affecting etonogestrel metabolism
Rifampin and rifabutin can accelerate metabolism leading to decreased hormone concentration
Certain antiepileptics like oxcarbazepine and topiramate may reduce implant effectiveness
St. John's Wort oral herbal supplement induces CYP3A4, potentially reducing efficacy
HIV medications including protease inhibitors and non-nucleoside reverse transcriptase inhibitors can interact adversely
Hepatitis C medications affecting liver metabolism may alter etonogestrel levels
Aprepitant and bosentan may alter hepatic enzyme activity impacting drug levels
Felbamate may reduce contraceptive hormone efficacy
Combination with other hormonal contraceptives or therapies should be cautiously managed
Effect of enzyme inducers may persist up to 28 days after discontinuation; additional non-hormonal contraception required during this period
Potential altered metabolism with drugs influencing cytochrome P450 enzyme system
Drugs affecting gastrointestinal absorption generally do not affect subdermal implant efficacy
No significant interactions expected with most non-hormonal medications
Healthcare providers should be informed of implant presence during any medication initiation or surgical procedure

Preparations Of The Drug

Nexplanon contains 68 mg of etonogestrel embedded in an ethylene-vinyl acetate copolymer matrix comprising 28% vinyl acetate
The implant is a single flexible rod approximately 4 cm in length and 2 mm in diameter
Radiopaque due to barium sulfate inclusion, enabling radiological localization
Inactive ingredients include magnesium stearate and barium sulfate to support drug delivery and implant visibility
The implant is packed sterile and intended for single subdermal insertion by trained healthcare professionals
Insertion kit includes sterile needle applicator and bandages for post-insertion care
Expiration period extends up to several years under recommended storage conditions prior to insertion
Designed for sustained release over 3 years followed by removal and potential replacement
Manufactured by N.V. Organon, a subsidiary of Organon & Co., with adherence to strict pharmaceutical standards
Packaging includes patient information leaflets, insertion and removal instructions
Storage conditions require protection from moisture and excessive heat
The implant material is biocompatible and flexible to minimize discomfort and mechanical failure
Disposal procedures post-removal adhere to biomedical waste management protocols
Prescription-only medication requiring healthcare provider administration and monitoring
No oral or parenteral formulations of etonogestrel are part of Nexplanon marketed presentation