Two models of levonorgestrel-releasing intrauterine devices were studied. Model A was designed to deliver 20 micrograms/day, and model B was designed to deliver 30 micrograms/day. Plasma concentrations of levonorgestrel were determined in blood samples taken from women who used the levonorgestrel-releasing intrauterine devices (IUDs) and who participated in a clinical trial for more than 5 years. During clinical studies IUDs have been removed for various reasons between 8 and 40 months after insertion. The rate of release of levonorgestrel from the IUDs was calculated by determining the remaining amount of levonorgestrel. Plasma concentrations of levonorgestrel ranged between a mean +/- standard deviation (SD) concentration of 166 +/- 75 pg/ml and 131 +/- 32 pg/ml for the first 18 months of use and between 101 +/- 37 pg/ml and 74 +/- 15 pg/ml at 24 and 60 months after insertion of the IUD. The plasma concentrations from 24 months through 60 months were significantly lower than concentrations measured during initial months of IUD use, but not between the two devices. There was a strong correlation between the time of use and the amount of levonorgestrel lost from the IUDs. The calculated mean daily release of levonorgestrel was 17.6 micrograms for model A and 22.2 micrograms for model B. This gives a calculated lifetime of more than 6 years for a levonorgestrel-releasing IUD.
PIP: 2 models of levonorgestrel-releasing IUDs were studied. Model A was designed to deliver 20 mcg/day and model B 30 mcg/day. Plasma concentrations of levonorgestrel were determined in blood samples taken from who had used the levonorgestrel-releasing IUDs and who had participated in a clinical trial for more than 5 years. During clinical studies, IUDs have been removed for various reasons between 8-40 months after insertion. The rate of release of levonorgestrel from the IUDs was calculated by determining the remaining amount of levonorgestrel. Plasma concentrations of levonorgestrel ranged between a mean +or- standard deviation concentration of 166 +or- 75 pg/ml and 131 +or- 32 pg/ml for the 1st 18 months of use and between 101 +or- 37 pg/ml and 74 +or- 15 pg/ml at 24 and 60 months after IUD insertion. Plasma concentrations from 24 to 60 months were significantly lower than concentrations measured during the initial months of IUD use, but not between the 2 devices. There was a strong correlation between the time of use and the amount of levonorgestrel lost from the IUDs. The calculated mean daily release of levonorgestrel was 17.6 mcg for model A and 22.2 mcg for model B. This gives a calculated lifetime of more than 6 years for a levonorgestrel-releasing IUD.