etonogestrel implant (Implanon)

single-rod, progestin-only, subdermal contraceptive Indications: - prevention of pregnancy for up to 3 years Contraindications: 1) pregnancy 2) history of thromboembolism 3) acute hepatic disease or tumor 4) 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: 1) spotting, menorrhagia or other vaginal bleeding irregularities (11-18%) 2) amenorrhea (22%) 3) headache (25%) 4) vaginitis (14%) 5) weight gain 14% 6) acne (14%) 7) mastodynia (13%) 8) upper respiratory tract infection (13%) 9) abdominal pain (11%) 10) pharyngitis (10%) Drug interactions: 1) potent inducers of cyt P450 3A4 may diminish effectiveness of implanon - rifampin, - antifungals - anticonvulsants - St John's wort - antiviral protease inhibitors 2) inhibitors of cyt P450 3A4 may increase concentrations of etonogestrel - itraconazole, ketoconazole Notes: cost (2006) $523

References

Prescriber's Letter 13(9): 2006 Etonogestrel Implant (Implanon) Detail-Document#: 220922 (subscription needed) http://www.prescribersletter.com