Evaluation of a 1-year levonorgestrel-releasing contraceptive implant: side effects, release rates, and biodegradability

Long-acting biodegradable implant for sustained delivery of antiretrovirals (ARVs) and hormones

Women worldwide confront two major reproductive health challenges: the need for contraception and protection from sexually transmitted infections, including Human Immunodeficiency Virus (HIV). Multipurpose Prevention Technologies (MPTs) that simultaneously prevent unintended pregnancy and HIV could address these challenges with a single product. Here, we developed a long-acting (LA) subcutaneously administered and biodegradable implant system that provides sustained delivery of contraceptive and antiretroviral (ARV) with zero-order release kinetics. The MPT system involves two implants comprising an extruded tube of a biodegradable polymer, poly(ε-caprolactone) (PCL). Each implant is filled with a formulation of progestin [levonorgestrel (LNG) or etonogestrel (ENG)], or a formulation of a potent ARV [tenofovir alafenamide (TAF), or 4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA)]. We demonstrated sustained in-vitro release of LNG, ENG, and EFdA from the implant system for 13-17 months, while maintaining high stability of the drugs (>99%) within the implant reservoirs. We further elucidated the controlled release mechanism of the implant and leveraged several tunable parameters (e.g., type and quantity of the excipient, PCL properties, and implant wall thickness) to tailor the release kinetics and enhance the mechanical integrity of the MPT implant. The optimized MPT showed sustained in-vitro release of ENG and EFdA over 1 year while maintaining a high level of formulation stability and structural integrity. The MPT implant system was further evaluated in a preclinical study using a rodent model and demonstrated sustained release of EFdA (6 months) and ENG (12 months) with high stability of the drug formulation (>95%). This manuscript supports the continued advancement of LA delivery systems for MPTs.

Advances in long-acting injectables, implants, and vaginal rings for contraception and HIV prevention

Worldwide, women face compounding reproductive health risks, including human immunodeficiency virus (HIV), sexually-transmitted infections (STIs), and unintended pregnancy. Multipurpose prevention technologies (MPTs) offer combined protection against these overlapping risks in singular prevention products that offer potential for simplified use, lower burden, higher acceptability, and increased public health benefits. Over the past decade, substantial progress has been made in development of extended-release MPTs, which have further potential to grant sexual and reproductive health autonomy to women globally and to offer choice for women to accommodate varying needs during their reproductive lives. Here, we highlight the advances made in injectable, implant, and ring delivery forms, and the importance of incorporating end-user preferences early in the research and development of these products.

Current and future contraceptive options for women living with HIV

INTRODUCTION

Among women living with HIV, half of the pregnancies are unintended. Effective contraception can prevent unintended pregnancies and consequently reduce maternal mortality and perinatal transmission of HIV. While contraceptive options available for all women also apply to women living with HIV, specific considerations exist to the use of contraception by women living with HIV.

AREAS COVERED

First, general principles guiding the use of contraception among women living with HIV are discussed, such as choice, method mix, relative effectiveness, and drug-drug interactions. Second, a detailed discussion of each contraceptive method and issues surrounding the use of that method, such as drug-drug interactions, follows. Third, future contraceptive options in advanced development for use by women or men are briefly discussed.

EXPERT OPINION

Contraceptive methods available to all women should also be accessible to women living with HIV. When the relative effectiveness of a contraceptive method is reduced, for example due to drug-drug interactions with antiretrovirals, the method should still be made available to women living with HIV with the appropriate information sharing and counseling. Greater research on various aspects of contraceptive use by women living with HIV and more comprehensive testing of co-administration of hormonal contraceptives and common medications used by these women are warranted.

Addressing gaps in the contraceptive method mix: methods in development

Despite the availability of a variety of contraceptive methods, millions of women still have an unmet need for contraceptive choices. Short-acting methods are plagued by issues with adherence, leading to imperfect or inconsistent use and subsequent unintended pregnancy. Long-acting contraceptive methods such as intrauterine devices and contraceptive implants, while providing highly effective and safe contraception, do not meet the needs of all women, often due to cost, access or acceptability issues. Several new methods are in various stages of development and are designed to address the shortcomings of current methods. Providers should be aware of these future options and how they might better meet women's needs.

The in vivo degradation, absorption and excretion of PCL-based implant

The in vivo degradation of poly (epsilon-caprolactone)(PCL) was observed for 3 years in rats. The distribution, absorption and excretion of PCL were traced in rats by radioactive labeling. The results showed that PCL capsules with initial molecular weight (Mw) of 66000 remained intact in shape during 2-year implantation. It broke into low molecular weight (Mw=8000) pieces at the end of 30 months. The Mw of PCL deceased with time and followed a linear relationship between logMw and time. Tritium-labeled PCL (Mw 3000) was subcutaneous implanted in rats to investigate its absorption and excretion. The radioactive tracer was first detected in plasma 15 days after implantation. At the same time radioactive excreta was recovered from feces and urine. An accumulative 92% of the implanted radioactive tracer was excreted from feces and urine by 135 days after implantation. In the mean while, the plasma radioactivity dropped to the background level. Radioactivity in the organs was all close to the background level confirming that the material did not cumulate in body tissue and could be completely excreted.

Implantable contraception

Although levonorgestrel contraceptive implants have been available for over 15 years, innovations have only recently led to a wider choice. These new implants offer easier insertion and removal and other advantages depending on the type of progestin. Implants prevent pregnancy by several mechanisms, including inhibition of ovulation and luteal function and alteration of cervical mucus and the endometrium. The high efficacy and ease of maintenance make implants an ideal contraceptive for many women, including adolescents, a population that uses implants infrequently but reports high satisfaction. Implants are appropriate for women who are breastfeeding, who have contraindications to estrogen, or who have diseases such as diabetes, hypertension, sickle cell anemia, or an HIV infection because implants have few metabolic or hematologic effects. Long-term use has not been associated with a decrease in BMD and generally leads to increased blood levels and iron stores. Women who wish to space their pregnancies appreciate the nearly immediate onset of action with insertion and the rapid termination of all effects with removal. All types of implants lead to menstrual changes and other side effects in some women. Adverse effects that occur in implant users more than the general population include headaches and acne. Women must be thoroughly counseled regarding the potential for menstrual alteration, side effects, and sexually transmitted infections if they do not use condoms. Despite their initial high cost, implants are a cost-effective method over several years, even when discontinued before the life of the implant.

The use of long-acting contraceptives in adolescents

DMPA and implants have played an important role in the attempt to prevent teenage pregnancies. Adolescent health care providers should provide continued counseling to girls using DMPA or implants and should promptly address any concern associated with these methods. Future studies are warranted to explore ways to prevent or reduce the side effects of DMPA and implants, as well as to develop new, optimal, long-acting contraceptives. Detailed baseline information should be obtained in every future study that explores the presence of side effects during the use of long-acting contraceptives.

Biodegradation and tumorigenicity of implanted plates made from a copolymer of epsilon-caprolactone and L-lactide in rat

Flat plates made from a copolymer of epsilon-caprolactone and L-lactide (P-CL-LA) [50:50 (w/w), molecular weight 1.62 x 10(5); 20 x 10 x 1 mm size] were subcutaneously implanted into 50 young, male Wistar rats (P-CL-LA group). After 24 months the plates had become a mass of small pieces, which were concentrated in an area of 3 x 2 x 1 mm. For comparison, 50 rats were implanted with medical-grade polyethylene plates (PE group) while another set of 50 rats was subjected to the same operation but without an implant (Sham Op group). Tumors arose in 25 rats from the P-CL-LA group: 24 were malignant mesenchymal tumors at the implant sites. In the PE group, tumors appeared in 16 rats (14 at the implant sites and two ectopically). The average tumor latency was 578+/-84 days in the P-CL-LA group and 452+/-102 days in the PE group. There was no difference in tumor incidence between the P-CL-LA and PE groups (p < 0.05). In the Sham Op group, two malignant tumors appeared over 2 years. Pathologically, these induced tumors arose from the inflammatory cells surrounding the degrading fragments of P-CL-LA within the tissue capsule. This indicates that relatively slowly degrading material can induce malignant tumors at a similarly high rate to nonabsorbable medical grade PE, at least in this animal model.

Serum concentrations of estradiol, progesterone, and levonorgestrel are not determinants of endometrial histology or abnormal bleeding in long-term Norplant implant users

The objective of this study was to determine the relevance of serum estradiol, progesterone and levonorgestrel concentrations to endometrial histology and uterine bleeding associated with long-term Norplant implants use. Eighteen five-year users of Norplant implants had endometrial biopsies and determinations of serum estradiol, progesterone and levonorgestrel concentrations. Correlations among these factors and uterine bleeding were calculated. Proliferative endometrium (but not sex steroid levels) was associated with abnormal bleeding. Neither ovarian steroid nor levonorgestrel concentrations was a predictor of abnormal bleeding. Hyperplastic changes were not seen even with high estradiol and low levonorgestrel levels.

Hormonal implants: contraception for a new century

Subdermal implants are contraceptive systems that release low, stable amounts of synthetic progestins from Silastic or other materials for periods of months to several years. Unlike other hormonal delivery systems, they do not cause unnecessary peaks in progestin levels and do not use estrogens, and thus their health risks are minimal. Norplant has been studied more extensively than any other subdermal contraceptive implant. More than 60,000 women have participated in clinical trials, which demonstrated that this approach is one of the most effective reversible contraceptive methods available (1% pregnancy rate in 5-year users). The implant also reduces the incidence of ectopic pregnancy to a level much below noncontraceptive users and about equivalent to TCu380A intrauterine device users. Exposure to the sustained, low dose of levonorgestrel delivered by Norplant has shown only minor metabolic changes. Side effects are minor but often bothersome, causing some discontinuation of the method. First-year continuation rates range from 76% to 90%. Fertility return after discontinuation is prompt. Difficulty in removal of the implant capsules by the less experienced practitioner has motivated researchers to develop systems that are easier to use, less obvious under the skin, and biodegradable. The Norplant 2 system is faster, easier, and less painful to insert and remove. Implants under investigation release desogestrel and other progestins; Capronor and subdermal norethindrone pellets are biodegradable systems.