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

Comparison of plasma etonogestrel concentrations sampled from the contralateral-to-implant and ipsilateral-to-implant arms of contraceptive implant users

OBJECTIVE

To compare plasma etonogestrel concentrations sampled from the contralateral- versus ipsilateral-to-implant arm.

STUDY DESIGN

Sub-analysis of a cross-sectional study in Botswana in 33 participants who provided contralateral and ipsilateral blood samples.

RESULTS

Plasma etonogestrel concentrations in contralateral and ipsilateral specimens were highly correlated (correlation coefficient = 0.99; p < 0.0001). Bland-Altman analysis of agreement showed that etonogestrel levels were on average 5.9 pg/mL higher (2.1%) in ipsilateral compared to contralateral specimens (95% confidence interval: -4.1, 15.9 pg/mL).

CONCLUSIONS

We found no meaningful differences in plasma etonogestrel concentrations between samples taken from the contralateral- versus ipsilateral-to-implant arm.

IMPLICATIONS

Our data suggest that etonogestrel plasma concentrations are unlikely to be meaningfully different between samples drawn from the ipsilateral- versus the contralateral-to-implant arms in etonogestrel contraceptive implant users.

An enzyme immunoassay for serum and urinary levonorgestrel in human and non-human primates

A microtiter plate enzyme immunoassay (EIA) is reported for the measurement of levonorgestrel (LNG) in serum and urine samples of human and non-human primates, and the results are compared to data obtained by radioimmunoassay (RIA). Rabbit polyclonal antibodies were raised against the bovine serum albumin conjugate of the 3-O-carboxymethyl oxime (CMO) derivative of LNG. The enzyme label was produced by the conjugation of horseradish peroxidase to LNG at the 3-position by the same CMO bridge used for the immunogen. The assay requires 2.5 hours to perform using 2.2-azino-di-(3-ethylbenzthiazoline sulfonic acid) diammonium salt as the chromogenic substrate. Serum (100 microliters) is extracted with petroleum ether prior to assay, whereas urine samples (25 microliters) are diluted and measured directly. The sensitivity of the assay is 0.25 pg/well with a 50% displacement of label at 7.5-9.5 pg and a linear response through 250 pg/well. Minimum levels of 8.7 and 10.0 pg/ml can be detected in serum and urine samples, respectively. Changes in serum LNG concentrations were measured in women and non-human primates following LNG implantation or injection. In the non-human primate study, serum LNG concentrations began to rise rapidly following i.m. injection of LNG, with peak levels occurring on days 3 to 5, then decreasing to approximately 25-35% of peak levels for the duration of the study. Circulating concentrations of 1.86 +/- 0.18 ng/ml LNG were reached in women the first week post-insertion of Norplant implants and decreased by 50% at 7-10 days, 75% after 14-21 days, followed by a steady decrease during the next 60-70 days to constant low levels that exhibited a high individual variation. Correlation coefficients of EIA and RIA results were 0.988 for human serum, 0.926 for human urine, and 0.972 for non-human primate serum.

Free levonorgestrel index and its relationship with luteal activity during long-term use of Norplant implants

Levonorgestrel serum levels and sex hormone binding globulin (SHBG) were measured in 82 women during different years of use of Norplant implants. The ratio between levonorgestrel and SHBG was calculated as an indicator of the free biologically active fraction of levonorgestrel (free levonorgestrel index, FLI). These parameters were then correlated with the presence of luteal activity, as determined by progesterone levels above 9.6 nmol/L, in a sampling run of 10 samples taken twice a week for five consecutive weeks. Levonorgestrel serum levels remained constant around 1.0 nmol/L during the five-year period. SHBG levels were below normal for the first 18 months of use, returning to normal levels during the last three years of use. The FLI in the first two years was significantly higher than that observed in the later years. The frequency of cycles with luteal activity was 12% during the first 2 years, increasing to 44% in the latter years, when FLI levels were lower. Our results suggest that the changes in SHBG and consequently in the free biologically active fraction of levonorgestrel may largely account for the differences in degree of ovarian suppression observed between the first two years of use of Norplant implants and the latter three, even in the absence of a significant variation in total levonorgestrel concentrations.

The effect of low-dose oral contraceptives and Norplant on blood pressure and body weight of Nigerian women

Blood pressure (BP) and body weight were assessed at entry, 6 months and 12 months of use in a prospective study of 117 and 76 women using low-dose oral contraceptives (LD-OCs) and Norplant, respectively. The results showed that mean systolic BP (mmHg), diastolic BP (mmHg) and weight (kg) for LD-OCs and Norplant at entry, 6 months and 12 months, respectively, were not significantly different. During the one year of use, the study found that moderate increase in BP occurred at the same frequency as reduced BP, and that observed variation in BP was within a narrower range in Norplant users compared with LD-OC users.

The effect of continuous subdermal levonorgestrel (Norplant) on carbohydrate metabolism

Blood glucose and plasma insulin levels during an oral glucose tolerance test were measured in 20 women using continuous subdermal levonorgestrel (Norplant) for contraception over a 12-month period. Changes in carbohydrate metabolism occurred as early as 1 month but were most marked after 6 months. After 1 month the area under the glucose and insulin curves increased by 12.3% and 37.7%, respectively. This increase was more marked by 6 months, but by 12 months it was significantly less marked. Although changes in the blood glucose and plasma insulin levels at different times during the oral glucose tolerance test occurred, they were all within normal limits for normal women. The peak blood glucose and insulin levels after insertion of the implant occurred 60 minutes after the glucose load, as opposed to 30 minutes before insertion. Apart from this, there was a significant delay in the return of these levels to fasting values. We conclude that this product, like any other progesterone-containing contraceptive, alters carbohydrate metabolism, but these alterations are not clinically significant in normal women. It is, however, possible that in potential cases of diabetes it may predispose to frank diabetes.

Changes in carbohydrate metabolism during 30 months on Norplant

During a 30-month period, changes in carbohydrate metabolism (measured by oral glucose tolerance test) were studied in 20 Norplant acceptors. Changes were first observed one month after Norplant insertion and peaked between 12-18 months. The area under the glucose curve rose by 12.3% and 40.5% one and 12 months post insertion, respectively. At 18, 24 and 30 months the rise was, respectively, 41.9%, 40% and 38.6%. Although the changes under the insulin curves were similar, the increase at one month was doubled (25.7%). Only fasting insulin values showed very slight and insignificant changes during the 30-month period. All the changes were, however, within the normal limits for healthy women. We conclude that although Norplant induces changes in carbohydrate metabolism, these changes remain within normal limits, peak at 12 months and either remain the same or decrease with time.

Plasma levels of levonorgestrel and free levonorgestrel index in women using NORPLANT implants or two covered rods (NORPLANT-2)

Plasma levels of levonorgestrel, sex hormone binding globulin (SHBG) and estradiol were studied during four years in 283 healthy women using either NORPLANT implants or two covered rods (NORPLANT-2). The women were randomized to use either type of implant. Both implant systems have previously been shown to have similar release rates of levonorgestrel. In both groups plasma levels of levonorgestrel decreased throughout the study, and there were no statistically significant differences between the two groups in mean plasma levels of levonorgestrel. During the study 8 women became pregnant. All pregnancies but one occurred after 35 months of implant use and only in women using the covered rods. No significant differences were seen between the women who became pregnant and the rest of the group using two covered rods with respect to plasma levels of levonorgestrel. SHBG capacity tended to be somewhat higher in women using the two covered rods. As levonorgestrel is to a great extent bound to SHBG, and in that form not biologically active, a "free levonorgestrel index" was calculated as a ratio between levonorgestrel and SHBG. This index was significantly lower in users of two covered rods than in users of NORPLANT implants at 1, 12 and 48 months of use. Women who became pregnant had significantly lower "free levonorgestrel index" than had the rest of the group. It is postulated that the difference in "free levonorgestrel index" between users of the two implant systems reflect differences in release rate, the covered rods having a lower release rate of levonorgestrel than NORPLANT throughout the observation period. It is concluded that "free levonorgestrel index" is a better parameter than levonorgestrel plasma levels to describe implant function, and to discriminate women who are at risk of pregnancy.

Ovulation detection following removal of levonorgestrel subdermal contraceptive implants

The time to resumption of ovulation following the discontinuation of levonorgestrel subdermal implants (Norplant) was assessed in 10 women. A blood sample (2 ml) was taken at the time of Norplant removal and then twice weekly until the first evidence of ovulation (serum progesterone concentration greater than or equal to 5 ng/ml) was documented. Ovulation was resumed in 80% of the cases by 3 weeks and in all the cases by 7 weeks. Prompt return of ovulation following Norplant removal is an additional advantage of this mode of long-acting contraception.

Plasma levonorgestrel and progesterone levels in women treated with silastic covered rods containing levonorgestrel

Levonorgestrel and progesterone plasma levels were measured in women bearing levonorgestrel subdermal implants. Two groups using four or six levonorgestrel covered rods and one group of non-hormonal contraceptors were compared. Blood samples were drawn twice a week for six consecutive weeks at different intervals after treatment administration. The mean levonorgestrel levels (mean +/- S.D.) observed in the four rods group was .49 +/- .13 ng/ml in the first year and decreased to .34 +/- .06 in the fifth year of treatment. The mean values observed in the six rods group were .70 +/- .15 ng/ml in the second year and .43 +/- .11 in the sixth year. The levonorgestrel plasma levels were slightly above those found with Norplantr implants in the four rods group and well above it in the six rod group. The highest plasma progesterone value found in each sampling period was above 9 nmol/l in 7 (14%) out of 50 subjects in the four rods group, in 2 (4.3%) out of 47 subjects in the six rods group and in all the 49 control women. In 4 out of the 7 subjects from the 4 rods group and in the two subjects from the 6 rods group, the highest progesterone value was preceded and followed by values lower than 6 nmol/l. It was concluded that the progesterone levels were seldom compatible with the occurrence of ovulation in women treated with four or six levonorgestrel covered rods which release an estimated daily dose of 70 and 105 micrograms, respectively.

Anovulation, inadequate luteal phase and poor sperm penetration in cervical mucus during prolonged use of Norplant implants

Blood samples for progesterone assay were collected for a total of 49 cycles, from 27 volunteers using the NORPLANT system. Levonorgestrel determinations were carried out in the same samples. A group of 12 women with normal cycles were studied in the same manner to serve as controls. Of the 49 cycles studied, 20 (41%) were ovulatory. The mean levonorgestrel level in ovulatory patients was 0.34 +/- 0.11 ng/ml (S.D.) compared to 0.42 +/- 0.14 ng/ml (S.D.) in anovulatory cycles. Compared to the control group, progesterone levels were significantly lower for users of NORPLANT implants during days -12 to -10 (p less than 0.025), -9 to -7 (p less than 0.05), -6 to -4 (p less than 0.0005) and days -3 to -1 (p less than 0.01). Cervical mucus evaluations and post-coital tests were done around mid-cycle in 29 of the cycles studied. All samples of cervical mucus were of poor quality, viscous and scarce, with a mean SPK of 4.1 +/- 2.3 cm. Most had absent or atypical ferning. Twenty-one subjects (73%) had a post-coital score of 1, and 4 (14%) of zero. Thus, anovulation, inadequate luteal phase and the direct effect of the continuous administration of levonorgestrel over cervical function, all seem to contribute to the effectiveness of NORPLANT implants.

Long-term experience with Norplant contraceptive implants in Finland

Silastic implants containing the progestin, levonorgestrel, were tested as a long-term contraceptive system in 124 women. During five years of use no accidental pregnancy occurred. The first year continuation rate was 90% and the five-year continuation rate was 54%, including terminations for wish to become pregnant. The medically relevant continuation rate was 68% after five years. Menstrual irregularities were the most frequent reason for termination, but only in the first two years. 70% of the terminations for that reason occurred during the first two years. Terminations for other steroid-related reasons were infrequent. The follow-up will continue up to the end of the seventh year. Seven of seventeen women who requested removal of the implants because they wanted to become pregnant conceived during the first two cycles and only three were not pregnant one year after removal.

Long-term reversible contraception with levonorgestrel-releasing Silastic rods

Subcutaneously placed Silastic capsules containing levonorgestrel are effective for 5 years and have a higher continuation rate than other methods of reversible contraception. Six 3 cm capsules are required to achieve satisfactory circulating levels of levonorgestrel. Two 4 cm covered Silastic rods containing levonorgestrel, which are easier to manufacture, insert, and remove than the capsules, produce similar in vitro release rates. This study compared clinical and metabolic effects as well as bleeding patterns in 23 women using either six capsules (n = 11) or two covered rods (n = 12). Serum levels of levonorgestrel, lipids, and lipoproteins as well as frequency of elevated progesterone levels were compared in serum samples obtained before treatment and 1, 6, 12, 18, and 24 months after insertion with the two systems. While bleeding patterns were similar for users of the two systems, rod users had slightly higher serum levels of levonorgestrel and a lower incidence of cycles with elevated progesterone levels. Therefore, rods could replace capsules as a long-term, reversible contraceptive method.