Progesterone-releasing vaginal rings for use in postpartum contraception. II. Pharmacokinetic profiles in women

In vitro release testing methods for drug-releasing vaginal rings

Drug-releasing vaginal rings are torus-shaped devices, generally fabricated from thermoplastic polymers or silicone elastomers, used to administer pharmaceutical drugs to the human vagina for periods typically ranging from three weeks to twelve months. One of the most important product performance tests for vaginal rings is the in vitro release test. Although it has been fifty years since a vaginal ring device was first described in the scientific literature, and despite seven drug-releasing vaginal rings having been approved for market, there is no universally accepted method for testing in vitro drug release, and only one non-compendial shaking incubator method (for the estradiol-releasing ring Estring®) is described in the US Food and Drug Administration's Dissolution Methods Database. Here, for the first time, we critically review the diverse range of test methods that have been described in the scientific literature for testing in vitro release of drug-releasing vaginal rings. Issues around in vitro-in vivo correlation and modelling of in vitro release data are also discussed.

Ovarian function during use of vaginal rings delivering three different doses of Nestorone

Contraceptive vaginal rings delivering various progestins alone or in combination with estrogen have been previously studied, showing adequate steroid vaginal absorption and acceptability by the users. Nestorone progestin (NES) is a potent 19-nor-progesterone derivative, inactive by the oral route, but an excellent option for vaginal delivery. The purpose of this study was to evaluate ovarian function during 6 months of continuous use of progestin-only vaginal rings delivering 3 different doses of NES: 50, 75, and 100 microg per day. Blood samples were taken twice a week for 5 consecutive weeks during a control cycle and on months 1, 3 and 6 of use, for the measurement of estradiol (E2), progesterone (P), and NES. A total of 87 volunteers randomly received each of the 3 doses. After an initial peak, NES serum levels remained fairly constant throughout the duration of the study at about 125, 200 and 250 pmol/L, respectively, decreasing slightly with time. Luteal activity occurred very rarely (1.2-2.6% of sampling periods) with no apparent difference between doses. Low E2 levels (< or =100 pmol/L) in all samples of a run were rare (5%) and only with the high dose ring (100 microg/day). E2 remained within normal levels (101-1500 pmol/L) in most of the segments studied. We conclude that the 50 and 75 microg/day NES rings provide adequate ovulation inhibition without hypoestrogenism, while the 100 microg/day ring may deliver an unnecessarily high dose.

Initial and steady-state pharmacokinetics of a vaginally administered formulation of progesterone

OBJECTIVE

The pharmacokinetics of a 100 mg vaginal progesterone suppository was evaluated on days 1 and 7 and a 200 mg suppository on day 14. All the volunteers were given oral 17 beta-estradiol during the study.

STUDY DESIGN

Ten postmenopausal women volunteered for this study. Progesterone was given as a vaginal suppository. Peripheral venous samples were obtained at appropriate intervals and analyzed for 17 beta-estradiol and progesterone levels. Area under the curve for progesterone was assessed by the trapezoidal method. Statistical analysis was performed by a one-way analysis of variance.

RESULTS

Serum 17 beta-estradiol levels ranged from 22 to 182 pg/ml. Maximal serum progesterone levels ranged from 5.7 to 20.9 ng/ml, with the mean maximal levels 13.97, 16.09, and 12.68 ng/ml (not significantly different) and a mean area under the curve of 168.13, 207.64 and 227.71 ng/ml per hour on days 1, 7, and 14 (not statistically different).

CONCLUSIONS

These data indicate that vaginal absorption of progesterone is efficient. The lack of difference in the area under the curve for both doses suggests that the vaginal mucosa or the total surface area of the vagina may limit the absorption of progesterone from the vagina.

The effect of small doses of progesterone released from two types of vaginal rings on ovarian activity and bleeding patterns during the first postpartum year

A total of 20 breastfeeding women used progesterone-releasing vaginal rings for up to 12 months. The women were divided into two groups, one (n = 9) using rings with an initial release rate of 5 mg/24 h, the other (n = 11) with a release rate of 20 mg/24 h. Individual women started to give breast milk supplements and ceased to breastfeed after various periods of time. Urinary estrone and pregnanediol glucuronide levels were measured by radioimmunoassay three times weekly during the entire trial. Individual diary cards were used to register bleeding and spotting. A significantly higher concentration of pregnanediol glucuronide was seen when the 20 mg/24 h ring was used in the lactation period, in comparison with the 5 mg/24 h ring. In the post-lactation period, pregnanediol glucuronide levels dropped when the 20 mg/24 h ring was used. Estrone glucuronide levels increased after the termination of breastfeeding, indicating an enhanced suppression of ovarian activity in the lactation period with both rings. Although the degree of suppression was dose-related, both rings were likely to offer a sufficient contraceptive effect in the lactation period. No significant changes were observed when milk supplements were added to breastfeeding. The use of the 20 mg/24 h ring resulted in a much better bleeding pattern (significantly less bleeding days) than the 5 mg/24 h ring during the lactation period. In the post-lactation period, the 20 mg/24 h ring the bleeding because much worse than in the lactation period.(ABSTRACT TRUNCATED AT 250 WORDS)

Progesterone-releasing vaginal rings for use in postpartum contraception. I. In vitro release rates of progesterone from core-loaded rings

Vaginal rings of Dow Corning 382 Silastic polymer, having identical outside dimensions, were fabricated to contain cores of different diameters loaded with 25% w/w progesterone. Elution of rings was carried out in continuously flowing baths of isotonic saline at 37 degrees C and quantities of progesterone released in 24 h periods measured for up to 128 days. Release of the steroid was shown to be a membrane diffusion-controlled process, modified by the development of a gradually increasing zone of depletion at the core surface. Rings of a suitable core diameter were selected to give initial release of 5 mg/24 h progesterone and sterile batches of these rings, prepared for WHO-sponsored clinical studies in post-partum, lactating women, were shown to give highly consistent and reproducible rates of in vitro drug delivery. A comparison was made with the in vitro release rates of rings containing a homogeneous dispersion of progesterone.