etonogestrel implant (Implanon)

Introduction

single-rod, progestin-only, subdermal contraceptive

Indications

• prevention of pregnancy for up to 3 years

Contraindications

• pregnancy
• history of thromboembolism
• acute hepatic disease or tumor
• breast cancer or high risk patient

Dosage

• Each rod contains 68 mg of etonogestrel, which releases etonogestrel
  • 60-70 ug/day for 5-6 weeks
  • 35-45 ug/day at 1 year
  • 30-40 ug/day at 2 years
  • 25-35 ug/day at the end of 3 years

Must be removed at the end of 3 year period; may be replaced by a new Implanon rod

Rod is 4 cm x 2 cm, preloaded disposable applicator

Implanted subdermally into the inner side of the non-dominant arm 6-8 cm above the elbow crease overlying the groove between the biceps & triceps.

Implant between days 1 & 5 of the menstrual cycle, within 7 days of the last oral contraceptive, or within 5 days of 1st trimester miscarriage or abortion.

Pharmacokinetics

• metabolized by cyt P450 3A4

Adverse effects

• spotting, menorrhagia or other vaginal bleeding irregularities (11-18%)
• amenorrhea (22%)
• headache (25%)
• vaginitis (14%)
• weight gain 14%
• acne (14%)
• mastodynia (13%)
• upper respiratory tract infection (13%)
• abdominal pain (11%)
• pharyngitis (10%)

Drug interactions

• potent inducers of cyt P450 3A4 may diminish effectiveness of implanon
  • rifampin,
  • antifungals
  • anticonvulsants
  • St John's wort
  • antiviral protease inhibitors
• inhibitors of cyt P450 3A4 may increase concentrations of etonogestrel
  • itraconazole, ketoconazole

Notes

cost (2006) $523

More general terms

• progestin-only implant

Components

• etonogestrel (3-oxodesogestrel)