Levonorgestrel plasma levels during continuous administration with different models of subdermal implants

Area of Science:

• Pharmacology
• Reproductive Health

Background:

• Subdermal levonorgestrel implants are a long-acting reversible contraceptive method.
• Understanding plasma levonorgestrel concentrations is crucial for assessing contraceptive efficacy and safety.

Purpose of the Study:

• To determine and compare plasma levonorgestrel concentrations in women using different types and configurations of subdermal levonorgestrel implants.
• To evaluate the long-term stability of levonorgestrel release from these implants.

Main Methods:

• Plasma levonorgestrel concentrations were measured in women using 6-capsule NORPLANT, 4-rod, and 6-covered rod subdermal implants.
• Blood samples were collected from both arms, with and without tourniquet application, to assess local and systemic levels.

Main Results:

• Levonorgestrel concentrations remained stable around 0.4 ng/ml for up to 6 years with 6-capsule NORPLANT.
• Plasma levels were constant around 0.55 ng/ml (4 rods) and 0.70 ng/ml (6 covered rods) for 3.5 years.
• Statistically significant differences (p < 0.0005) were observed in mean levonorgestrel concentrations between the groups.
• Local concentrations in the arm with implants were 2-3 times higher than in the contralateral arm.

Conclusions:

• Subdermal levonorgestrel implants demonstrate consistent plasma levonorgestrel levels over extended periods.
• Variations in implant design and number affect systemic levonorgestrel exposure.
• Local drug concentrations at the implant site are significantly higher than systemic levels.