By Dr. Shruti Bhat
Sustained and controlled-release devices for drug delivery in the vaginal and uterine areas are most often for the delivery of contraceptive steroid hormones. The advantages in administration by this route--prolonged release, minimal systemic side effects, and an increase in bioavailability-- allow for less total drug than with an oral dose. First-pass metabolism that inactivates many steroids hormones can be avoided.
One such application is the medicated vaginal ring. Therapeutic levels of medroxy progesterone have been achieved at a total dose that was one-sixth the required oral dose and ring expulsion, to name a few. Microcapsules have also recently been useful for vaginal and cervical delivery. Local progesterone release from this dosage form can alter cervical mucus to interfere with sperm migration. Other steroids have also attained sustained delivery by an intracervical system. The sustained release of progesterone from various polymers given vaginally have also been found useful in cervical opening and induction of labor.
A more common contraceptive device is the intrauterine device (IUD). The first intrauterine devices used were of the unmedicated type. These have received increased attention since the use of polythylene plastics and silicone rubbers. These materials had the ability to resume their shape following distortion. Because they are unmedicated, these IUDs cannot be classified as sustained release products. It is believed their mechanism of action is due to local endometrial responses, both cellular and cytosecretory. Initial investigations of these devices led to the conclusions that the larger the device, the more effective it was in preventing pregnancy. Large devices, however, increased the possibility of uterine cramps, bleeding, and expulsion of the device.
Efforts to improve IUD’s have led to the use of medicated devices. Two types of agents are generally used, contraceptive metals and steroid hormones. The metal device is exemplified by the CU-7, a polypropylene plastic device in the shape of number 7. Copper is released by a combination of ionization and chelation from a copper wire wrapped around the vertical limb. This system is effective for up to 40 months.
The hormone-releasing devices have a closer resemblance to standard methods of sustained release because they involve the release of a steroid compound by diffusion.
In the coming chapters, we shall discuss on controlled release injections, implant delivery systems, quality control of CRDDS, Regulatory considerations and Novel CRDDS.............
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By Dr. Shruti Bhat
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