Recovery of fertility after removal of polyurethane plugs from the human vas deferens occluded for up to 5 years

Advances in Male Contraception: When Will the Novel Male Contraception be Available?

Many contraceptive methods have been developed over the years due to high demand. However, female contraceptive pills and devices do not work for all females due to health conditions and side effects. Also, the number of males who want to actively participate in family planning is gradually increasing. However, the only contraceptive options currently available to males are condoms and vasectomy. Therefore, many male contraceptive methods, including medication (hormonal and non-hormonal therapy) and mechanical methods, are under development. Reversibility, safety, persistence, degree of invasion, promptness, and the suppression of anti-sperm antibody formation are essential factors in the development of male contraceptive methods. In this paper, male contraceptive methods under development are reviewed according to those essential factors. Furthermore, the timeline for the availability of a new male contraception is discussed.

Male contraception: narrative review of ongoing research

BACKGROUND

Since the release of the combined oral contraceptive pill in 1960, women have shouldered the burden of contraception and family planning. Over 60 years later, this is still the case as the only practical, effective contraceptive options available to men are condoms and vasectomy. However, there are now a variety of promising hormonal and non-hormonal male contraceptive options being studied. The purpose of this narrative review is to provide clinicians and laypeople with focused, up-to-date descriptions of novel strategies and targets for male contraception. We include a cautiously optimistic discussion of benefits and potential drawbacks, highlighting several methods in preclinical and clinical stages of development.

RESULTS

As of June 2023, two hormonal male contraceptive methods are undergoing phase II clinical trials for safety and efficacy. A large-scale, international phase IIb trial investigating efficacy of transdermal segesterone acetate (Nestorone) plus testosterone gel has enrolled over 460 couples with completion estimated for late 2024. A second hormonal method, dimethandrolone undecanoate, is in two clinical trials focusing on safety, pharmacodynamics, suppression of spermatogenesis and hormones; the first of these two is estimated for completion in December 2024. There are also several non-hormonal methods with strong potential in preclinical stages of development.

CONCLUSIONS

There exist several hurdles to novel male contraception. Therapeutic development takes decades of time, meticulous work, and financial investment, but with so many strong candidates it is our hope that there will soon be several safe, effective, and reversible contraceptive options available to male patients.

Male Contraception

Approximately 40 to 50% of pregnancies are unintended. Contraceptive use significantly reduces the risk of unintended pregnancy. Approximately 70% of couples' contraceptive use is female and 30% is male, attributable to the reliance on condoms and vasectomies. Unfortunately, many women cannot use currently available contraceptives due to medical contraindications or side effects. At the same time, men want additional safe and effective contraceptive methods. Because of this, work to develop novel, safe, and effective male contraceptives is underway. This review will briefly discuss the pros and cons of condoms and vasectomies, and then describe research into the development of novel methods of male contraception, by the mechanism of action of the contraceptive. First, we will discuss male contraceptives that block sperm transmission. Next, we will discuss male contraceptives that impair sperm production. Lastly, we will discuss male contraceptives that impair sperm function.

Update on Novel Hormonal and Nonhormonal Male Contraceptive Development

BACKGROUND

The advent of new methods of male contraception would increase contraceptive options for men and women and advance male contraceptive agency. Pharmaceutical R&D for male contraception has been dormant since the 1990s. The Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) has supported a contraceptive development program since 1969 and supports most ongoing hormonal male contraceptive development. Nonhormonal methods are in earlier stages of development.

CONTENT

Several hormonal male contraceptive agents have entered clinical trials. Novel single agent products being evaluated include dimethandrolone undecanoate, 11β-methyl-nortestosterone dodecylcarbonate, and 7α-methyl-19-nortestosterone. A contraceptive efficacy trial of Nestorone®/testosterone gel is underway. Potential nonhormonal methods are at preclinical stages of development. Many nonhormonal male contraceptive targets that affect sperm production, sperm function, or sperm transport have been identified.

SUMMARY

NICHD supports development of reversible male contraceptive agents. Other organizations such as the World Health Organization, the Population Council, and the Male Contraception Initiative are pursuing male contraceptive development, but industry involvement remains limited.

Emerging approaches to male contraception

Despite significant interests in contraception by men, effective methods of male contraception are limited to vasectomy and condoms. Recently, there have been several promising advances in male contraceptive research. This review will update readers on recent research in both hormonal and nonhormonal approaches to male contraception. Hormonal approaches to male contraception have been stymied by adverse effects, formulations requiring injections or implants, a 5% to10% nonresponse rate, as well as poor understanding of user acceptability. In the last several years, research has focused on novel, orally bioavailable androgens such as dimethandrolone undecanoate and 11β-methyl-19-nor-testosterone. Additionally, combinations of a topical testosterone gel combined with a gel containing segesterone acetate, a potent progestin, have shown promise in clinical trials recently. Simultaneously, significant preclinical progress has been made in several approaches to nonhormonal male contraceptives, including compounds that inhibit sperm motility such as eppin, compounds that inhibit retinoic acid binding or biosynthesis, and reversible approaches to obstruction of the vas deferens. It is imperative for these areas of research to continue making strides so that there is a gamut of contraceptive options for couples to choose from. Some of these approaches will hopefully reach clinical utility soon, greatly improving contraceptive choice for couples.

Development of Novel Male Contraceptives

Unintended pregnancy is surprisingly common, accounting for 40-50% of pregnancies worldwide. Contraception is the most effective means of preventing unintended pregnancy. Seventy percent of all contraceptives are used by women; however, some women are unable to use contraceptives due to health conditions or side effects. Many men wish to take a more active role family planning, but currently have only two effective male contraceptive options, condoms and vasectomy. Therefore, work to develop novel male contraceptives analogous to popular female methods, such as daily pills or long-acting shots and implants, is underway. This paper will briefly discuss the pros and cons of condoms and vasectomies, and then review the research into novel methods of male contraception.

Male contraception

Although female contraceptives are very effective at preventing unintended pregnancy, some women can not use them because of health conditions or side-effects, leaving some couples without effective contraceptive options. In addition, many men wish to take active responsibility for family planning. Thus, there is a great need for male contraceptives to prevent unintended pregnancies, of which 80-90 million occur annually. At present, effective male contraceptive options are condoms and vasectomy, which are not ideal for all men. Therefore, efforts are under way to develop novel male contraceptives. This paper briefly reviews the advantages and disadvantages of condoms and vasectomies and then discusses the research directed toward development of novel methods of male contraception.

Azoospermia in rabbits following an intravas injection of Vasalgel ™

BACKGROUND

Vasectomy is currently the only long-acting contraceptive option available for men, despite increasing demand and potentially significant positive impacts on human health of additional male contraceptive options. Vasalgel ™ is a high molecular weight hydrogel polymer being developed as a non-hormonal long-acting reversible male contraceptive. Vasalgel consists of styrene-alt-maleic acid dissolved in dimethyl sulfoxide, which is distinct from styrene-alt-maleic anhydride materials previously studied.

METHODS

The goal of the study was to determine the contraceptive efficacy of two test articles with different levels of styrene maleic acid (100 %, and 80 % acid/20 % anhydride). The test articles were injected bilaterally in the vasa deferentia of mature male rabbits. Post-implantation analyses of semen parameters were completed over a 12 month period and compared to baseline measures of sperm concentration, motility and forward progression.

RESULTS

Both test articles were effective in blocking the passage of spermatozoa through the vasa deferentia in the 12 subjects completing the study. A significant decrease in sperm concentration occurred following implantation of the test material, with no measurable sperm concentration except for a few samples in one animal that were markedly oligospermic. Vasalgel produced a rapid onset of azoospermia, with no sperm in semen samples collected as early as 29-36 days post-implantation, and was durable over a 12 month period.

CONCLUSION

This study indicated that Vasalgel is an effective non-hormonal long-acting male contraceptive in a rabbit model.

Beyond the Condom: Frontiers in Male Contraception

Nearly half of all pregnancies worldwide are unplanned, despite numerous contraceptive options available. No new contraceptive method has been developed for men since the invention of condom. Nevertheless, more than 25% of contraception worldwide relies on male methods. Therefore, novel effective methods of male contraception are of interest. Herein we review the physiologic basis for both male hormonal and nonhormonal methods of contraception. We review the history of male hormonal contraception development, current hormonal agents in development, as well as the potential risks and benefits of male hormonal contraception options for men. Nonhormonal methods reviewed will include both pharmacological and mechanical approaches in development, with specific focus on methods which inhibit the testicular retinoic acid synthesis and action. Multiple hormonal and nonhormonal methods of male contraception are in the drug development pathway, with the hope that a reversible, reliable, safe method of male contraception will be available to couples in the not too distant future.

Haute Autorité de santé. [Male and female sterilization techniques: Summary of ANAES assessments (May 2005)]

OBJECTIVE

To summarize assessments carried out by ANAES on male and female sterilization techniques. The summary was requested by the French Health Directorate after the law authorizing sterilization as a means of contraception was passed.

RESULTS (FEMALE STERILIZATION)

(i) EFFICACY of tubal ligation, electrocoagulation, clips or rings: the annual pregnancy rate is 0-2% depending on the study, with no significant difference between techniques. No data were found on fimbriectomy. (ii) EFFICACY of a hysteroscopically placed micro-insert device: no pregnancies were observed in patients with bilateral tube obstruction diagnosed by hysterosalpingography at 3 or at 6 months after placement (placement rate: 87-89%). (iii) SAFETY of tubal ligation, electrocoagulation, clips or rings: (a) By approach: There was no difference in the incidence of major complications between laparoscopy and minilaparotomy but there were significantly fewer minor complications with laparoscopy than with minilaparotomy. There were significantly more major complications with culdoscopy than with minilaparotomy and significantly more minor complications than with laparoscopy. (b) By operative technique: major and minor complications were significantly more common with the Pomeroy technique than with electrocoagulation; the difference could be due to the approach used. No data were available on fimbriectomy. (iv) SAFETY of a hysteroscopically placed micro-insert device: there were 11 cases of myometrial or tubal perforation among 734 patients (with device displacement into the peritoneal cavity in 3 cases).

RESULTS (MALE STERILIZATION)

(i)

EFFICACY

efficacy varied from 84% to 100% depending on the approach and the mode of vas deferens obstruction. There was no significant difference in efficacy according to approach (transcutaneous or scrotal). However, no conclusion could be drawn on the comparative efficacy of the occlusion techniques used from published data. (ii)

SAFETY

the rate of postoperative complications was low, below 10% in most series. Complications were benign and only rarely necessitated surgical revision.

CONCLUSION

The advantage of sterilization methods is that they lack any permanent contraindication. They should be presented as being generally irreversible. Fimbriectomy is not recommended for female sterilization. Laparoscopy is the preferred approach. Sterilization by hysteroscopic placement of a micro-insert device should be restricted to cases presenting a risk on laparoscopy; the technique should be re-assessed in 2006. The two approaches used for male sterilization are technically similar and do not seem to differ in efficacy. The Public Health Code states that "Fallopian tube or deferens duct ligation for contraceptive purposes is not allowed in minors" and that ligation "cannot be performed unless the adult involved has given his/her informed and motivated consent, expressed after taking into consideration clear, complete information on the consequences of the procedure". A waiting period of four months must follow the moment the decision to sterilize is taken and consent is given. An informed consent form must be signed. Sterilization in young or nulliparous women should be proposed with the greatest prudence and with many reservations.

Efficacy of percutaneous vas occlusion compared with conventional vasectomy

OBJECTIVES

To determine the efficacy, evaluate the safety and assess side-effects (swelling, haematoma and pain) of percutaneous vas occlusion compared with vasectomy in Dutch men.

PATIENTS AND METHODS

Vas occlusion and vasectomy procedures (attempted in 58 and 50 men, respectively) were conducted at the University Hospital Maastricht. The men returned 1 week after the procedure, underwent a clinical examination and completed a questionnaire assessing subjectively any pain, swelling and haematoma. The men were asked to return for semen analysis at 6 and 12 weeks and, if necessary, for additional analyses until they were azoospermic.

RESULTS

The vas occlusion procedure was completed on both vasa in 49 of the 58 men (84%) in whom it was attempted. Significantly more (P < 0.001) men were azoospermic after vasectomy (48 of 50) than after vas occlusion (only four). Men undergoing vas occlusion reported significantly less pain (P = 0.02), swelling (P = 0.01) and haematoma (P = 0.04) after the procedure than did men undergoing vasectomy.

CONCLUSION

Men undergoing vas occlusion would not have been able to rely on the method for contraception. From this study, vas occlusion, at least in its current form, is an unsuitable method of male contraception. Not only was the efficacy poor, but constraints in delivering the method in its current state would probably limit its utility, especially in situations where resources are limited.

Male contraception

With the powerful tools of molecular investigation, the last decade has witnessed the most remarkable scientific advance in our history, yet no new leads for male contraception have been forthcoming. All the likely methods of male contraception discussed above were derived from relatively 'old' physiological principles or serendipitous observations. The increasing gap between fundamental research (in the control of mammalian spermatogenesis) and the lack of clinical application are a testament to the low public funding priority afforded to male reproduction and the unwillingness of the pharmaceutical industry to invest in male reproductive research and development. Yet amidst such an unfavourable setting and with very limited support, it is heartening to note that the prospects of introducing a new systemic method for male contraception into the market by the end of this millenium has been greatly enhanced. Thus the results of recent studies have confirmed the contraceptive efficacy of sex steroid-induced oligozoospermia and unexpectedly revealed an ethnically distinct pattern of susceptibility to the hormonal suppression of spermatogenesis. Thus, Asian men are more responsive than are caucasian, and long-acting testosterone esters now being tested in that most densely populated part of the world may well hasten the large-scale application of this method. This is probably the most effective way to correct the misconceptions that men are unwilling or disinterested in sharing in family planning options with their partners. Together with the increased acceptance of novel non-surgical and reversible methods of vas deferens occlusion and the availability of improved non-latex condoms, the currently unfulfilled contraceptive needs of millions of men can be increasingly met in future years. The consequent increase in overall contraceptive prevalence could well make the telling difference between demographic catastrophe and maintaining good quality existence. Politicians, scientists and industrialists need to wake up to their responsibilities and the opportunities offered by this untapped resource and market potential.

Sterilization

Sterilization is accepted as a permanent method of contraception by many couples in the world. Female sterilization is more widely used than male sterilization, but the latter is used by many couples in developed countries. The most widely used methods for female sterilization are simple tubal ligation, electrocautery of the fallopian tubes, and occlusion of the tubes by Hulka or Filshie clips or Falope rings. These procedures may be carried out either by minilaparotomy or by laparoscopy, under local anaesthesia. Sterilization may be performed immediately following pregnancy, or as an interval operation. The effectiveness of female sterilization is high, with failure rates of about 1-2 per 1000 procedures. Immediate complications are few and minor, while there appear to be no serious, long-term adverse effects. It is possible that there is a protective effect against ovarian cancer. Potential new technologies for female sterilization include the use of chemicals, such as quinacrine, for transcervical tubal occlusion, and hysteroscopic methods. Male sterilization is more simple and can readily be performed under local anaesthesia. A new technique originating in China, the no-scalpel technique, has made the procedure even more simple and produces fewer complications such as haematoma. It is possible that the direct injection of plug-forming material into the vas may render the procedure more reversible. Concerns about possible adverse effects of vasectomy on cardiovascular diseases and testicular cancer largely have been dispelled, but a possible weak association between vasectomy and prostatic cancer continues to be studied.

Intravasal injection of formed-in-place medical grade silicone rubber for vas occlusion

This paper describes two consecutive studies: a volume study and an efficacy study. The volume study determined the appropriated volume of Medical Grade Silicone Rubber (MSR) needed to achieve complete occlusion of the vas deferens. This was done by in-vitro testing of 130 human vas specimens containing plugs of MSR formed in vivo. The volume of MSR needed to occlude the vas was 0.1531 +/- 0.0059 ml injected by five to six turns of the applicator handwheel. There was a correlation between MSR volume, weight, and the number of turns of the applicator handwheel. An influence of body height upon the volume and weight of the MSR was also observed. An oval shaped clamp (15 mm long) was more effective in producing secure vas occlusion than was a round clamp (10 mm long). The mean outer diameter of the vas specimens was 1.80 +/0 0.15 mm, and the mean maximum dilated inner diameter was 0.93 +/- 0.11 mm. The efficacy study was a clinical trial to compare MSR was occlusion (using an oval 15 mm clamp and the appropriate volume derived from the volume study, n = 58) with no-scalpel vasectomy as the standard procedure (n = 64). The azoospermia rate following MSR vas occlusion was not significantly different from that following no-scalpel vasectomy, and was achieved in 3-6 months.

Vasal sterilization in China

Vasal sterilization has become the most popular method of contraception in many countries since the 1960's. In China, an estimated 30 million men have undergone voluntary sterilization. There have been two major developments in vasectomy technique, the no-scalpel method and the percutaneous chemical vas occlusion. These methods have significantly increased the acceptability of male sterilization in some cultures since no incisions in the skin are required. The effective rate is over 98% for both methods. The clients experience less pain, fewer complications and more rapid recovery. Epidemiological studies of large numbers of volunteers receiving no-scalpel or chemical vas occlusion procedures have resulted in a clearer picture of their safety, effectiveness, simplicity and economy. Meanwhile, some promising reversible vasal sterilization techniques have also been studied.

Intravasal injection of formed-in-place silicone rubber as a method of vas occlusion

This report describes the procedure for percutaneous injection of silicone to form plugs in the vas deferens. The injection of 0.1-0.16 ml Chinese-made silicone into 14 men achieved occlusion of a 1-cm length of the vas. Sperm concentrations declined within 1 month of the operation and azoospermia was achieved in all men by 9 months.