Implants contain a progestogen in a slow-release carrier, made either of dimethylsiloxane, as in Jadelle (not available in the UK) with two implants, or ethylene vinyl acetate (EVA), as in Implanon, a single rod (Figure 12). They are excellent examples of long-acting reversible contraceptives (LARCs), with the ideal ‘forgettable’ default state, yet rapid reversibility. | Contraceptive implants Implants contain a progestogen in a slow-release carrier made either of dimethylsiloxane as in Jadelle not available in the UK with two implants or ethylene vinyl acetate EVA as in Implanon a single rod Figure 12 . They are excellent examples of long-acting reversible contraceptives LARCs with the ideal forgettable default state yet rapid reversibility. Figure 12 Implanon courtesy of Organon Laboratories Ltd . Note that current advice is to insert anterior to the site shown see text . 90 Mechanism of action administration and effectiveness Implanon works primarily by ovulation inhibition supplemented mainly by the usual sperm-blocking mucus effect. It is a single 40 mm rod just 2 mm in diameter containing 68 mg of etono-gestrel - the chief active metabolite of desogestrel - and so has much in common with Cerazette. This is dispersed in an EVA matrix and covered by a mm rate-limiting EVA membrane. Clinically Implanon is inserted subdermally but very superficially under the skin over the biceps medially in the upper arm under local anaesthesia from a dedicated sterile preloaded applicator by a simple injection-and-withdrawal technique - aided by the blunt bevel of its cleverly shaped wide-bore needle. Current teaching contrary to the SPC is to insert superficial to the biceps muscle and anterior to the groove between the triceps and biceps well away from the neurovascular bundle. Although this implant is much easier than Norplant to insert or remove specific model arm plus live training is essential and cannot be obtained from any book. In the UK the best training is obtainable through the Faculty of FP. The manufacturer Organon can provide names of Faculty-approved trainers. After an initial phase of several weeks giving higher blood levels Implanon delivers almost constant low daily levels of the hormone for a recommended duration of use of 3 years. In the pre-marketing trials Implanon had the unique distinction of a zero failure rate .
