I'm sure many of you, who have explored the use of Estrogens, have wondered why subcutaneous Estrogen implants are not readily available in this country, but can be found in Europe and Australia. Implantable Estrogens have been used in humans for over 50 years, but have not gained in popularity for many reasons. First, there is only one medically available preparation of crystalloid 17 beta Estradiol marketed by Organon International under the name of Riselle. It is not sold in this country. Other preparations are made for the Veterinary market to increase meat yields in cows and sheep. Ironically the European Union has banned the use of these growth hormones in any of its imported or domestic beef. Second, the insertion of these pellets measuring 4.5 mm in diameter and 2 cm in length requires a small surgical incision with a surgical stitch or adhesive for closure. They are placed under the skin of the abdomen or buttocks with a long hollow trocar using local anesthesia. They are usually palpable, but are difficult to remove if they cause persistent discomfort. Third, depending on the biodegradable material used to encase the crystals, the release into the blood stream has been shown to vary from 33-155 picograms/dl per day. Although the drug company says the absorption into the blood stream is consistent for any one individual, there are only 3 small studies measuring estradiol levels in relation to bone density. In the other studies the effectiveness of the absorption is judged by the relief of climacteric symptoms or in the case of transsexuals by the measurement of breasts and hips.

If we adhere to the principle that the smallest amount of estrogen, that produces the desired physical change is the best, then we cannot know the blood levels acquired with implants unless we measure the Estradiol blood level every month. Estradiol implants come in 25mg, 50mg, 75mg and 100mg doses to be inserted every 6 months.  In England TSs have been treated with mega doses of 100mg implants every other month producing supra-physiologic levels of Estradiol and increased complications of blood clotting, nausea and pain at the injection site. It is commonly agreed that a blood level of 200-250 pcgs/dl should be achieved to realize breast development, but these patients had levels over 1000 - 1500 , which put them at greater risk for complications. When the company was called to task for this, they said there were no complications if used properly and would not withdraw this dosage. A well controlled study of 50 menopausal women showed that when a 25 mg implant was given every 6 months a consistent level of around 200 could be achieved and sustained, but the group with a 50 mg implant did not have levels much above this. The most interesting problem with this method of dosing is called tachyphylaxsis. This is where after approximately 6 months, the estrogens seem to produce no additional changes requiring continued increases in the Estrogen dose for maintenance. Tachyphylaxsis may not happen at the 25mg dose, but after 2-3 years the accumulation of Estrogen results in unusually high blood levels. This again is peculiar to this method of dosing. This does not happen with the patch or oral estrogens, which can be stopped or reduced at any time.  Please remember that the transdermal patch is only delivering 100 micrograms, not 100 milligrams (1:1,000), of Estradiol twice a week. As with the patch, the implant avoids the first pass through the liver and intestines, which improves its safety profile to a degree. All the other side effects seen with Estrogens are seen with implants.

In this country the FDA has consistently refused to approve subcutaneous implants because the company has not provided sufficient data for safety and usage. California Blue Cross has a position paper stating that subcutaneous HRT is only investigational and not medically necessary.  Therefore they will not reimburse you as they might for approved Hormonal Therapy as part of your transitioning process.

Best of Luck in Your New Future,

Cerise Richards, M.D.