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Levonorgestrel subdermal implants. Contraception on trial.
When they were introduced to the world market in the 1980s, levonorgestrel subdermal implants offered the promise of an exciting alternative to traditional hormonal contraception. They provide highly effective, long-acting protection from pregnancy, without the need for user compliance. Broad acceptability of the drug has been reported throughout the world. Recently, however, the implants have met with opposition. The drug is associated with a variety of adverse effects, and removal of implants can be problematic. Serious events have been reported in women using levonorgestrel subdermal implants, although causal relationships have not been demonstrated. Additionally, concerns have been raised over the potential for coercive use of the drug. Numerous law suits have been filed alleging serious problems with implants. As a result, the drug has received considerable negative media attention. Before the controversy over levonorgestrel subdermal implants erupted, contraceptive development had declined, resulting from limitations to profits and funding, legal threats, and changes in the insurance industry. The levonorgestrel subdermal implant experience may serve to accelerate this trend. While the introduction of levonorgestrel subdermal implants offered an alternative to the current array of medical contraception, its experience may serve to dampen future contraceptive development efforts. Costly litigation and much controversy involving the implants have acted to create disincentives to further research and development of new methods of medical contraception.
How the field of controlled-release technology began, and its central role in the development of angiogenesis research.
The first controlled-release methodology was developed in 1962 and was based upon diffusion of small molecules (molecular weight less than 500) through the wall of silicone rubber tubing. The problem of controlled-release of large molecules such as proteins was not solved until more than a decade later, when it was discovered that microchannels formed around lyophilized proteins embedded in polymers such as ethylene vinyl acetate copolymer (EVA) and poly(hydroxyethylmethacrylate) (pHEMA), as water permeated through the polymer. These studies led to the development of a 5-year contraceptive implant, e.g., Norplant; rapid progress in the field of angiogenesis research; and a method for regulating cell shape and growth control in vitro.