IMPLANON 68MG/ROD IMPLANT

Indications

• Contraception in females of childbearing potential
• Long-term reversible contraception

Dosage

Children: Refer to the BNF for Children for guidance on contraceptive use in adolescents.

Adults: One subdermal implant (etonogestrel 68 mg) is inserted during the first five days of the menstrual cycle and can remain in place for up to three years.

Mechanism of action

Etonogestrel binds with high affinity to progesterone receptors in target organs such as the female reproductive tract, mammary gland, hypothalamus, and pituitary. This binding leads to changes in protein synthesis that result in decreased levels of gonadotropin-releasing hormone and luteinizing hormone, thereby inhibiting ovulation.

Pharmacodynamics

Etonogestrel inhibits fertility by impairing the release of luteinizing hormone, which is crucial for ovulation. It also increases the viscosity of cervical mucus, which hinders sperm passage, and alters the uterine lining to prevent implantation of fertilized eggs. Clinical trials have shown a failure rate of 0.1% over three years of use, with a rapid return to fertility upon removal of the implant.

Pharmacokinetics

After subdermal implantation, etonogestrel is released at a rate of 40 mcg daily, providing continuous contraception for up to three years. The pharmacokinetics involve high binding affinity to plasma proteins, and it is metabolized primarily in the liver. The mean elimination half-life is approximately 24 hours, and it reaches steady-state concentrations within a few days of implantation.

Contra-indications

• Acute porphyrias
• Current breast cancer

Adverse effects

• Headache
• Nausea
• Breast tenderness
• Irregular menstrual bleeding
• Mood changes

Interactions

• Etonogestrel + ulipristal may decrease efficacy
• Antiepileptics (e.g., carbamazepine, phenytoin) may decrease efficacy
• Modafinil may decrease efficacy
• Rifamycins may decrease efficacy
• St. John's Wort may decrease efficacy
• Ritonavir may decrease efficacy

Precautions

• Cardiac dysfunction
• Cervical cancer
• Diabetes
• History of stroke (including transient ischemic attack)
• Migraines with aura
• Multiple risk factors for cardiovascular disease

Pregnancy

Etonogestrel is contraindicated in pregnancy. It is a progestogen used for contraception.

Breast-feeding

Etonogestrel can be used during breastfeeding, typically advised after 6 weeks postpartum.

Storage

Store below 25°C. Protect from light and moisture.

Formulations

• Etonogestrel 68 mg subdermal implant

Mechanism of action

Etonogestrel binds with high affinity to the progesterone receptors in the target organs. From the target organs, they include the female reproductive tract, mammary gland, hypothalamus, and pituitary. Once bound, this drug changes the synthesis of different proteins which in order decreases the level of gonadotropin-releasing hormone and the luteinizing hormone. There is no evidence that etonogestrel has affinity for estrogen receptors.

Pharmacodynamics

Etonogestrel attains its therapeutic effect inhibiting fertility by impairing the release of the luteinizing hormone which is one of the most important reproductive hormones for ovulation. As well, etonogestrel is known to increase the viscosity of the cervical mucus hindering the passage of the spermatozoa and altering the lining in the uterus to prevent the implantation of the fertilized eggs in the endometrium. In clinical trials, etonogestrel was implanted and reported to avoid 100% of pregnancies over a three year period. When the implant was removed, normal periods were reinstalled within 90 days in 91% of the individuals. Fertility was established quickly with 20 reported pregnancies within 3 months of implant removal. The implants of etonogestrel release 40 mcg of etonogestrel daily and they usually provide a continuous contraception effect for 3 years. When the implant is administered, the failure rate is reported to be 0.1%. Some non-contraceptive effects are improved dysmenorrhea. All data of etonogestrel comes from patients between 80-130% of the body mass.