Usage
- Etonogestrel is prescribed for contraception (preventing pregnancy).
- Pharmacological Classification: Progestin (a synthetic form of progesterone, a female hormone).
- Mechanism of Action: Etonogestrel primarily works by suppressing ovulation (release of an egg from the ovary). It also thickens cervical mucus, making it difficult for sperm to enter the uterus, and thins the uterine lining, making it less receptive to implantation of a fertilized egg.
Alternate Names
- International Nonproprietary Name (INN): Etonogestrel
- Brand Name: Nexplanon (subdermal implant)
- Etonogestrel is also a component (along with ethinyl estradiol) in some combined hormonal contraceptives, like the vaginal ring NuvaRing.
How It Works
- Pharmacodynamics: Etonogestrel’s primary contraceptive effect is achieved by suppressing ovulation. The thickening of cervical mucus and changes to the endometrium are secondary mechanisms that further reduce the likelihood of pregnancy.
- Pharmacokinetics:
- Absorption: After the single-rod implant is placed under the skin, etonogestrel is released continuously at a decreasing rate over three years. Initial release is 60-70 mcg/day, decreasing to 35-45 mcg/day by the end of the first year, 30-40 mcg/day by the end of the second year, and 25-30 mcg/day by the end of the third year.
- Metabolism: Primarily metabolized in the liver by CYP3A4 enzymes.
- Elimination: Excreted mainly in urine and to a lesser extent in feces.
- Mode of Action: Etonogestrel binds to progesterone receptors, exerting its effects through genomic and non-genomic mechanisms. This leads to downregulation of gonadotropin-releasing hormone (GnRH), inhibiting the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the pituitary gland. The reduced LH surge prevents ovulation.
- Elimination Pathways: Primarily hepatic metabolism (CYP3A4) followed by renal and fecal excretion.
Dosage
Standard Dosage
Adults:
A single Nexplanon implant (68 mg etonogestrel) is inserted subdermally in the inner side of the upper, non-dominant arm. This provides contraception for up to 3 years.
Children (Postmenarchal Adolescents):
The dosage is the same as for adults. Use in premenarchal girls is not indicated.
Special Cases:
- Elderly Patients: Not indicated for use in postmenopausal women.
- Patients with Renal Impairment: No specific dosage adjustments are necessary.
- Patients with Hepatic Dysfunction: Contraindicated in women with active liver disease or liver tumors.
- Patients with Comorbid Conditions: Use with caution in patients with conditions that may be aggravated by fluid retention (e.g., heart failure, hypertension). For conditions such as diabetes, hypercholesterolemia, and hyperlipidemia, careful monitoring is advised.
Clinical Use Cases
Etonogestrel is specifically indicated for long-term contraception, and its use in settings like intubation, surgical procedures, mechanical ventilation, ICU, or emergency situations is not relevant.
Dosage Adjustments
No formal dose adjustments are necessary for renal impairment. However, for hepatic impairment, it is contraindicated. Concomitant use of CYP3A4 enzyme-inducing drugs can reduce etonogestrel effectiveness, and alternative or additional contraception should be considered.
Side Effects
Common Side Effects:
- Menstrual irregularities (changes in bleeding patterns, prolonged or irregular bleeding, amenorrhea)
- Weight gain
- Headache
- Acne
- Mood changes
- Breast tenderness
- Vaginitis
Rare but Serious Side Effects:
- Ectopic pregnancy (pregnancy outside of the uterus)
- Thromboembolic events (blood clots)
- Allergic reactions
- Ovarian cysts
- Breast cancer (although the overall risk is small)
- Elevated liver enzymes
Long-Term Effects:
- Potential for bone mineral density loss with prolonged use (although the clinical significance is uncertain).
Adverse Drug Reactions (ADR):
- Anaphylaxis (severe allergic reaction)
- Angioedema (swelling under the skin)
- Hepatic dysfunction
Contraindications
- Known or suspected pregnancy
- Current or past history of venous thromboembolism
- Active liver disease or liver tumors
- Undiagnosed abnormal genital bleeding
- Known or suspected breast cancer or other progestin-sensitive cancers
- Hypersensitivity to etonogestrel or any component of the implant
Drug Interactions
- CYP450 Interactions: Drugs that induce CYP3A4 (e.g., rifampin, carbamazepine, St. John’s Wort) can decrease etonogestrel effectiveness.
- Other Interactions: Some anticonvulsants, certain antibiotics (rifampin, rifabutin), and HIV medications may reduce etonogestrel’s contraceptive effect.
Pregnancy and Breastfeeding
- Pregnancy Safety Category: X (contraindicated in pregnancy)
- Fetal Risks: If pregnancy occurs with the implant in place, removal is recommended.
- Breastfeeding: Can be used after 4 weeks postpartum. Small amounts of etonogestrel are excreted in breast milk, but no significant effects on infant growth or development have been observed. May slightly reduce milk production.
Drug Profile Summary
- Mechanism of Action: Suppresses ovulation, thickens cervical mucus, thins uterine lining.
- Side Effects: Menstrual changes, weight gain, headache, acne, mood changes.
- Contraindications: Pregnancy, thromboembolic disorders, liver disease, breast cancer.
- Drug Interactions: CYP3A4 inducers, some anticonvulsants and antibiotics.
- Pregnancy & Breastfeeding: Contraindicated in pregnancy; can be used after 4 weeks postpartum.
- Dosage: Single 68 mg implant, subdermal, every 3 years.
- Monitoring Parameters: Monitor for signs of thromboembolism, hepatic dysfunction, and mood changes. Periodic blood pressure checks.
Popular Combinations
Etonogestrel is not typically used in combination with other drugs for contraceptive purposes.
Precautions
- General Precautions: Assess for contraindications and risk factors.
- Specific Populations: See above.
- Lifestyle Considerations: Smoking increases the risk of cardiovascular complications in women using hormonal contraceptives.
FAQs (Frequently Asked Questions)
Q1: What is the recommended dosage for Etonogestrel?
A: A single 68 mg implant is inserted subdermally, providing contraception for up to 3 years.
Q2: How effective is Etonogestrel?
A: Nexplanon is over 99% effective in preventing pregnancy.
Q3: Can Etonogestrel be used in breastfeeding women?
A: Yes, it’s generally considered safe to use after 4 weeks postpartum.
Q4: What are the most common side effects?
A: Menstrual irregularities (changes in bleeding patterns), weight gain, headache, acne, mood changes.
Q5: When should the implant be inserted?
A: Ideally, during the first five days of the menstrual cycle. Specific guidelines apply when switching from other contraceptive methods.
Q6: How is the implant removed?
A: A healthcare professional removes the implant with a minor surgical procedure under local anesthesia.
Q7: Does Etonogestrel protect against STIs?
A: No, Etonogestrel offers no protection against sexually transmitted infections.
Q8: What should I do if I experience severe pain or swelling after implant insertion?
A: Seek immediate medical attention as this could indicate a complication.
Q9: How long does it take for fertility to return after implant removal?
A: Fertility typically returns rapidly after removal, often within weeks.
Q10: Are there any drug interactions I should be aware of?
A: Yes, certain medications (especially enzyme inducers) can reduce Nexplanon’s effectiveness. Consult with a doctor about potential drug interactions.
