Long-term contraception by steroid-releasing implants. II. A preliminary report on long-term contraception by a single silastic implant containing norethindrone acetate (ENTA) in women

Current status of fertility control methods in India

Approximately 48.2% of couples of 15 to 49 years of age practice family planning methods in India. Female sterilization accounts for 34.2%, with male sterilization declining from 3.4% in 1992-93 to 1.9% in 1998-99. Use of the condom increased to 3.1% from 2.4%. There is an urgent need for research to develop new contraceptive modalities especially for men and also for women and to make existing methods more safe, affordable and acceptable. Current efforts in India to develop a male contraceptive are mainly directed towards (i) development of antispermatogenic agents to suppress sperm production, (ii) prevention of sperm maturation, (iii) prevention of sperm transport through vas deferens or rendering these sperm infertile and (iv) prevention of sperm deposition. Research work in the field of prevention of sperm transport through vas deferens has made significant advances. Styrene maleic anhydride (SMA) disturbed the electrical charge of spermatozoa leading to acrosome rupture and consequent loss in fertilizing ability of sperm. A multicentre phase-III clinical trial using SMA is continuing and it is hoped that the SMA approach would be available in the near future as an indigenously developed injectable intra-vasal male contraceptive. The safety and efficacy of available oral contraceptives were evaluated. An indigenously developed oral contraceptive 'Centchorman', which is a nonsteroidal, weakly estrogenic but potently antiestrogenic, was found to be safe and effective and is now being marketed in India since 1991 as a 'once a week' pill. Cyclofem and Mesigyna have been recommended as injectable contraceptives with proper counselling and service delivery by Indian studies. It has been recommended that these injectable contraceptives be added to the existing range of contraceptive methods available in the National Family Planning Programme. Based on the Indian studies CuT 200 was also recommended. Studies have indicated the advantage of intrauterine devices (IUD); they are long acting, relatively easily removed and fertility returns rapidly after their removal. Recent studies have recommended CuT 200 for use up to 5 years. The combination of some plant products i.e. Embelia ribes, Borax and Piper longum has been found to be safe and effective as a female contraceptive and the results of phase-I clinical trials are encouraging. Research work is going on in the country in various areas with special reference to hormonal contraceptive - a three monthly injectable contraceptive, immuno-contraceptives, antiprogestins, etc.

Bioavailability of norethindrone and menstrual pattern after insertion of norethindrone acetate implants in rhesus monkeys

Subdermal silastic implants releasing norethindrone acetate were inserted in five rhesus monkeys for a period of seven months. The serum norethindrone (NET) levels were estimated from blood samples collected fortnightly. There was an initial high level of NET followed by fluctuating levels of NET in 4 out of five monkeys. The serum NET values showed individual variation between time periods as well as between monkeys. The analysis of menstrual cycles showed initial amenorrhoea up to day 120-140 in four out of five monkeys. Only one monkey showed vaginal bleeding pattern comparable to normal menstrual cycles; this monkey had serum NET levels less than 10 ng/ml. The pharmacokinetic and pharmacodynamic parameters were similar to those reported in the human female.

Effect of progestins, estradiol, and coenzymes NAD and NADPH on the interconversion of estradiol and estrone in rabbit uterus in vitro

The biotransformation of estradiol (E2) and estrone (E1) in the uterus of rabbits treated with norgestrel (NG), norethindrone (NET), norethindrone acetate (NETA), progesterone (P4), and E2 either by subcutaneous injection in oil or by intrauterine steroid-releasing silastic implants was carried out under an in vitro short-term incubation system. The studies have shown that E2 stimulates 17 beta-hydroxysteroid dehydrogenase (17 beta-OHSD) much more than P4 as compared to untreated controls. The kinetic studies on E2 metabolism in the presence of added coenzyme NAD showed an initial rapid estrone formation and a gradual reconversion of E1 to E2. The addition of NADPH, ATP, and glucose-6-phosphate facilitates the reconversion of E1 to E2. The interconversion of E2 and estrone in the presence of coenzymes was five- to ten-fold higher in the endometrium than in the myometrium per milligram protein. Both E2 and progestins stimulate the uterine 17 beta-OHSD activity in rabbit uterus. This study further suggested that the hormone-induced metabolism of estradiol and estrone in the rabbit uterus is essentially modulated by the availability of coenzymes.

Clinical evaluation of the Capronor contraceptive implant: preliminary report

Capronor, a single-capsule, biodegradable, subdermal contraceptive that releases levonorgestrel over a 12- to 18-month period, has been evaluated in 48 healthy women, ages 18 to 40 years. Sixteen participants received a 2.5 cm capsule (12 mg of levonorgestrel), and 32 received a 4.0 cm capsule (21.6 mg of levonorgestrel). Serum levonorgestrel levels were significantly lower in the 2.5 cm group. Ovulation occurred in all cycles in the 2.5 cm group and in 26.3% of cycles in the 4.0 cm group. Levonorgestrel levels with the shorter capsule were too low for reliable contraception in all users, and 4 cm may be a minimal functional length. Bleeding patterns were regular in most women who ovulated and irregular in most remaining subjects. It is assumed that changes in cervical mucus and the endometrium contributed to effective contraception despite the frequency of ovulation.

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.

Somatic tissue responses of male rhesus monkeys treated with a contraceptive steroid formulation

Rhesus monkeys (Macaca mulatta) were treated with testosterone (100 micrograms/kg/day) plus estradiol (0.5 micrograms/kg/day) via subcutaneous polydimethylsiloxane (PDS; Silastic) implants for thirteen months. This steroid regimen inhibited dramatically spermatogenesis. Gross and histopathological examination of the musculoskeletal, circulatory, endocrine (excluding the testis), central nervous, gastrointestinal and respiratory systems failed to uncover any untoward effects of the long-term exposure due to the contraceptive formulation. Similarly, no remarkable effects were observed in the ionic, chemical and formed elements of blood or secondary sex structures. Failure to detect secondary complications attributed to the steroid treatment offers further justification for evaluating a contraceptive strategy based on administering naturally occurring steroids at sustained rates approximating those at which they are produced endogenously in the human male.

Long-term contraception with a single implant of the progestin ST-1435

Silastic capsules containing the synthetic progestin ST-1435 was inserted in 282 women of reproductive age who desired long-term contraception. Each woman received a single implant for 6 months' use. After evaluating the experience of the first 45 subjects, replacement capsules were offered to women desirous of continuing the method after the initial 6 months of use. In the first 6-month segment one pregnancy and 1720 woman-months of use were recorded. The total experience, through as many as six segments of use was 3373 woman-months of use and one pregnancy. The Pearl Index is 0.36 per 100 woman-years. The single pregnancy, recorded in the 1st month of the first segment, may represent a conception prior to implant placement. Amenorrhea was the most common side effect reported, with 83% of the women having at least one nonbleeding interval longer than 60 days during the first segment of use.

Plasma levels of norethindrone and effect upon ovarian function during treatment with silastic implants containing norethindrone

The study was made to evaluate the effect upon the ovarian steroid pattern during treatment with subcutaneously implanted silastic rods containing norethindrone. Four rods, each containing 37 mg norethindrone (NET), were implanted subcutaneously in five women and left in place for 135--200 days. Plasma levels of NET, estradiol and progesterone were determined by radioimmunoassays. After an initial peak found in all subjects, the plasma level of NET declined. Great day-to-day variations of NET were found. Ovulations were suppressed during treatment in three subjects. One subject had regular ovulations throughout treatment and in one subject a single ovulation was recorded. Peaks of estradiol without subsequent ovulation were found in two subjects. The bleeding pattern was irregular; three subjects had varying degrees of spotting and bleeding, two subjects were amenorrheic. The average daily release rate was 300/micrograms, calculated from the amount of steroids lost from the removed rods. This study indicates that the release of steroid from four NET rods is high enough only initially to completely inhibit ovulation.

Metabolic and endocrine studies in women using norethindrone acetate implant

Subcutaneously administered implant-D containing 40 mg of Norethindrone acetate in a single silastic implant was offered to 79 subjects who desired spacing of their family. The effect of constant release of steroid from this device on metabolic and endocrine functions was studied. Each subject in the pretreatment state served as her own control. The device was removed at 8 months initially and subsequently at 5-6 months. The clinical acceptability of this method was fairly high. The results reported in this study show that Norethindrone acetate administered in this way did not cause any adverse reactions on endocrine and metabolic functions as gauged by the parameters analysed.

Radioimmunoassay of norethindrone : serum levels of norethindrone in lactating women after insertion of a single Silastic implant releasing norethindrone acetate

A specific radioimmunoassay was developed for the estimation of norethindrone levels in the serum of lactating women. A conjugate of norethindrone-3-BSA was synthesized and antiserum raised against it in rabbits. The antiserum showed high affinity (1.5 x 10(9)M/L) and titer and was specific. The sensitivity of the assay was 125 pg/ml serum. Serum levels of norethindrone were estimated in 25 lactating women, inserted with subdermal implant releasing about 150 ug of norethindrone acetate daily. The norethindrone levels were initially high in the first two months. From there onwards the levels of norethindrone remained constant with an average value of 1.0 ng/ml up to six months. These values were comparable to those obtained in non-lactating women. Thus, lactation does not seem to alter or affect the release of norethindrone acetate from the subdermal implant or its metabolism.

Interaction of progestins with steroid receptors in human uterus

Norethindrone (17beta-hydroxy-19-nor-17alpha-pregn-4-en-20-yn-3-one) and norethindrone acetate (17beta-acetoxy-19-nor-17alpha-pregn-4-en-20-yn-3-one) interfered to a varying degree, by competitive inhibition, with the binding of progesterone and oestradiol to respective cytoplasmic receptors in the human uterus. Progesterone binding to 4S macromolecule was saturable and co-specific for progestins. Competitors like norgestrel (17beta-hydroxy-18-methyl-19-nor-17alpha-pregn-4-en-20-yn-3-one), 19-norprogesterone, medroxyprogesterone acetate (17alpha-acetoxy-6alpha-methylpregn-4-ene-3,20-dione) and compound R(5020) (17,21-dimethyl-19-norpregna-4,9-diene-3,20-dione) possessed higher binding affinities for the progestin receptor. The dissociation constant (K(d)) for the progesterone-receptor interaction was 0.6-1.6nm and the receptor concentration ranged between 6600 and 8200 sites/cell. Norethindrone and norethindrone acetate competed for the progesterone receptor with inhibition constants (K(i)) of 6.8 and 72nm respectively. Gradient displacement and competitive-receptor assays indicated that norethindrone acetate-binding affinity for progestin receptor was approximately one-tenth that of norethindrone and progesterone. The progestins also inhibited oestradiol binding to 4.6S oestrogenic receptor by 8-12%, involving interaction at the oestradiol-binding site with a calculated K(i) value of 0.5-0.8mum. The competitive interaction of progestins with steroid receptors may be of putative importance in explaining the progestin action at the target site.

Contraceptive and sterilization practices and extrauterine pregnancy: a realistic perspective

Comparative data on the incidence of ectopic pregnancy among accidental pregnancies associated with failure of a contraceptive or sterilization procedure are shown in Table 16. The practical clinical significance of the data in this review is predicated upon a number of related factors. One of the most important of these is the realistic failure rate (or success rate) of each contraceptive or sterilization method. The reported efficacy of various contraceptive methods has such a wide range that we have not attempted to calculate the likelihood that a woman may experience an ectopic pregnancy within a particular time period while using a specific method. The success or failure rate of each method is influenced by such variables as (1) the conscientiousness and ability of the patient to follow instructions, (2) the true failure rate of the method itself, (3) the experience of the clinician prescribing a method or performing a surgical procedure, and (4) other factors less clearly defined. Because of these many variables, the data shown in Table 16 were calculated on the basis of the number of reported accidental pregnancies which occurred coincidentally with, or subsequent to, a specific contraceptive or sterilization modality. (formula: see text). These data do not reflect the actual rate of occurrence of ectopic pregnancy with respect to woman-months of experience. We recognize the significant influence that age, race, gravidity, and socioeconomic factors have upon the incidence of ectopic pregnancy, but were unable to control for these factors in the data presented in this review. These data reprresent only what has occurred under specific circumstances and cannot logically be extrapolated to any specific future case or study series. It is important to emphasize the necessity of constant awareness by the medical and paraprofessional personnel of the potentially increased risk to the patient of an extrauterine pregnancy should one or another of these contraceptive or sterilization procedures fail. Complacency or a false sense of security on the part of responsible medical personnel concerning women who are "protected against conception" can quickly lead to a life-threatening situation in case of an ectopic pregnancy. Prompt diagnosis and definitive treatment of the extrauterine pregnancy is vital for the successful management of this serious complication of conception.