16.17: Intrauterine Drug Delivery Systems

Controlled-release systems for intravaginal and intrauterine drug delivery have been developed primarily for the administration of contraceptive steroid hormones. These delivery routes circumvent first-pass hepatic metabolism, thereby enhancing bioavailability and allowing for reduced systemic dosages compared to oral administration. Such approaches contribute to improved therapeutic efficacy and patient compliance, particularly in long-term contraceptive regimens.

Intravaginal Drug Delivery Systems

Intravaginal drug delivery systems are engineered to provide sustained release of hormonal agents. These include matrix diffusion-controlled devices, such as those incorporating medroxyprogesterone acetate within a silicone elastomer, and dissolution-controlled systems where progestins and estrogens are dispersed in a polyethylene glycol (PEG) and silicone matrix. A common formulation is the vaginal ring, which is manufactured via extrusion of the drug-silicone composition into a doughnut-shaped device. These rings typically release hormones for approximately 21 days, maintaining a cyclic hormonal profile for contraceptive efficacy.

Intrauterine Drug Delivery Systems (IUDs)

Intrauterine delivery systems are designed for extended contraceptive effectiveness, typically exceeding 12 months. Two primary types of medicated IUDs are widely utilized:

1. Copper Medicated IUDThis device is composed of a plastic framework—commonly shaped as a “T” or the number “7”—made from polypropylene or polyethylene. Copper wire, wound around the frame, releases ions locally upon oxidation in body fluids. The copper induces a cytotoxic effect on sperm, thereby preventing fertilization. A surface area of approximately 200 mm² maximizes contraceptive activity, allowing the device to remain effective for over three years.
2. Progesterone-Releasing IUD (Progestasert)This is also a T-shaped device containing a reservoir of progesterone dispersed in a silicone matrix. The hormone is released through a rate-controlling ethylene-vinyl acetate copolymer membrane at a daily dose of approximately 65 micrograms. The design ensures sustained hormone delivery and contraceptive action for up to one year.

These controlled-release systems exemplify the integration of pharmaceutical technology with reproductive healthcare, offering both short- and long-term contraceptive options.

Intravaginal drug delivery systems bypass first-pass metabolism, enhancing bioavailability and often making them more efficient than oral administration.

These systems include matrix diffusion-controlled devices, like medroxyprogesterone acetate in silicone, and dissolution-controlled devices, using progestin and estrogen dispersion in PEG and silicone.

Such devices are often formulated as vaginal rings, which provide sustained hormone release for up to 21 days, offering a cyclic intravaginal contraception.

For long-term contraception, intrauterine devices or IUDs are commonly used as they remain effective for 12 months to several years, depending on the device type.

Copper IUDs, commonly T- or 7-shaped, gradually release copper ions that exert a localized contraceptive effect lasting over three years.

The progesterone-releasing IUD is also a T-shaped device that releases progesterone dispersed in a silicone polymer through a controlled membrane.

As a result, it provides a consistent hormone dose, offering effective contraception for up to one year.