Injectable testosterone undecanoate has more favourable pharmacokinetics and pharmacodynamics than testosterone enanthate

Development of new hormonal male contraception for the couple

BACKGROUND

Current options for male contraception are limited to condoms, the withdrawal method, or a vasectomy. Studies indicate that men have expressed growing interest in bearing responsibility for family planning.

OBJECTIVES

To review prior studies investigating the role of an androgen-only or androgen with progestin regimen for hormonal male contraception and to provide an update of a promising new hormonal agent, a transdermal gel.

DISCUSSION

Thus far, there have been six studies conducted in couples evaluating the contraceptive efficacy of an androgen-only or androgen co-administered with a progestin regimen for hormonal male contraception. The only ongoing study is by the National Institute of Child Health and Human Development, in collaboration with the Population Council. They have developed a novel transdermal gel containing testosterone and segesterone acetate (Nestorone), a progestin. An ongoing phase II study enrolling more than 460 couples has shown great potential with respect to the product's efficacy, safety, reversibility, and acceptability. As this agent advances in development, a rapid at-home test for sperm concentration will provide couples with immediate feedback regarding their potential for pregnancy.

CONCLUSION

There is promise for the first-of-its-kind hormonal male contraceptive, a transdermal gel, to achieve market approval for distribution in the United States and elsewhere. Its safety, efficacy, reversibility, and user-control are all appealing qualities that make it readily adoptable for clinical practice.

Safety Aspects and Rational Use of Testosterone Undecanoate in the Treatment of Testosterone Deficiency: Clinical Insights

Testosterone deficiency is diagnosed by a serum total testosterone level below 300 ng/dL in combination with symptoms such as decreased energy and libido. These symptoms can be ameliorated by restoring serum testosterone to the physiologic range with testosterone therapy (TT). There are numerous forms of testosterone therapy, such as injectable, transdermal, nasal, and subcutaneous applications. There are also multiple formulations of injection, such as testosterone cypionate, testosterone enanthate, and testosterone undecanoate. Testosterone undecanoate (TU) is a long-acting ester formulation of testosterone that can be provided in an injectable or oral form. Oral testosterone undecanoate is marketed as Andriol, Jatenzo, Tlando, and Kyzatrex. Oral TU provides a convenient option for many patients, which may increase compliance with TT. Injectable testosterone undecanoate is marketed as Aveed and Nebido. Injectable TT remains the most cost-effective therapeutic option and is appropriate for most patients as an initial therapy. This review describes the pharmacokinetics of these testosterone undecanoate products and provides a guide for prescribers using these medications. While many forms of testosterone are appropriate for TT, a patient-centered discussion focused on goals of care should best guide physician prescription of these medications.

Testosterone Therapy With Subcutaneous Injections: A Safe, Practical, and Reasonable Option

CONTEXT

Injections with intramuscular (IM) testosterone esters have been available for almost 8 decades and not only result in predictable serum testosterone levels but are also the most inexpensive modality. However, they are difficult to self-administer and associated with some discomfort. Recently, subcutaneous (SC) administration of testosterone esters has gained popularity, as self-administration is easier with this route. Available data, though limited, support the feasibility of this route. Here we review the pharmacokinetics and safety of SC testosterone therapy with both long- and ultralong-acting testosterone esters. In addition, we provide guidance for clinicians on how to counsel and manage their patients who opt for the SC route.

EVIDENCE ACQUISITION

Systematic review of available literature on SC testosterone administration including clinical trials, case series, and case reports. We also review the pharmacology of testosterone absorption after SC administration.

EVIDENCE SYNTHESIS

Available evidence, though limited, suggests that SC testosterone therapy in doses similar to those given via IM route results in comparable pharmacokinetics and mean serum testosterone levels. With appropriate training, patients should be able to safely self-administer testosterone esters SC with relative ease and less discomfort compared with the IM route.

CONCLUSION

Although studies directly comparing the safety of SC vs IM administration of testosterone esters are desirable, clinicians should consider discussing the SC route with their patients because it is easier to self-administer and has the potential to improve patient adherence.

Exploring the Role of Testosterone Replacement Therapy in Benign Prostatic Hyperplasia and Prostate Cancer: A Review of Safety

Increased risk of prostate diseases triggered by testosterone replacement therapy (TRT) remains a worldwide concern. That said, we reviewed the safety of TRT in the spheres of benign prostatic hyperplasia (BPH) and prostate cancer (PCa), exploring clinical findings in this regard. Compelling evidence based on meta-analyses of randomized and observational studies indicates safety for TRT in patients suffering from prostate disorders such as BPH and PCa, at the same time improving lower tract urinary symptoms. Thus, the harmful relationship geared toward androgens and BPH seems to be overestimated as TRT has sufficient safety and, if properly prescribed, may counteract several metabolic problems. Even after PCa treatment, the benefits of TRT could outweigh the risk of recurrence, but further long-term randomized clinical trials are needed to elucidate unresolved questions.

Long-term testosterone undecanoate treatment in the elderly testosterone deficient male: An observational cohort study

BACKGROUND

Quarterly intramuscular injections with long-acting testosterone undecanoate (TU) provide stable serum testosterone concentrations over time and are therefore preferred by many testosterone-deficient patients. However, the use of long-acting TU in elderly patients is limited due to lack of safety and feasibility studies.

OBJECTIVE

To investigate long-acting TU pharmacokinetics and assess differences in treatment regimens and risk of adverse outcomes in younger versus elderly testosterone-deficient patients.

MATERIALS AND METHODS

Single-center longitudinal observational study. Patients who initiated long-acting TU treatment between 2005 and 2010 were included. Elderly patients were born before 1956 and younger patients between 1965 and 1985. TU dose was adjusted yearly through shortening or prolongation of time between injections. Treatment targets were as follows: (1) free testosterone between 0 and -1 SD from the age-adjusted mean, (2) no symptoms of testosterone deficiency, and (3) hematocrit within the normal range.

RESULTS

The study population consisted of 63 elderly and 63 younger patients. Median follow-up time during testosterone replacement was 12.1 years. Increasing intervals between TU injections were performed 44% more often in the elderly compared to younger patients and time between TU injections were prolonged 4% more in the elderly patients. The hematocrit, as well as the hematocrit for a given serum testosterone (hematocrit: testosterone ratio), increased with treatment time but did not differ between age groups. During follow-up, 40% of patients-both elderly and younger-experienced polycythemia. Risk of polycythemia did not differ with age.

DISCUSSION AND CONCLUSION

An increased number of adjustments of TU dose are necessary in elderly patients in order to reach treatment targets. TU treatment in elderly testosterone-deficient patients is not associated with an increased risk of polycythemia compared to younger patients if age-adjusted treatment targets are reached.

Prevalence of polycythaemia with different formulations of testosterone therapy in transmasculine individuals

BACKGROUND

Masculinising hormone therapy with testosterone is used to align an individual's physical characteristics with his or her gender identity. Testosterone therapy is typically administered via intramuscular or transdermal routes, and polycythaemia is the most common adverse event.

AIMS

To compare the risk of polycythaemia with different formulations of testosterone therapy in transmasculine individuals.

METHODS

A retrospective cross-sectional analysis was undertaken of transmasculine individuals at a primary and secondary care clinic in Melbourne, Australia. A total of 180 individuals who were on testosterone therapy for >6 months was included. Groups included those receiving: (i) intramuscular testosterone undecanoate (n = 125); (ii) intramuscular testosterone enantate (n = 31); or (iii) transdermal testosterone (n = 24). Outcome was prevalence of polycythaemia (defined as haematocrit > 0.5).

RESULTS

Mean age was 28.4 (8.8) years, with a median duration of testosterone therapy of 37.7 (24.2) months; 27% were smokers. There was no difference between groups in serum total testosterone concentration measured. While there was no difference between groups in haematocrit, there was a higher proportion of patients with polycythaemia in those who were on intramuscular testosterone enantate (23.3%) than on transdermal testosterone (0%), P = 0.040. There was no statistically significant difference in polycythaemia between intramuscular testosterone undecanoate (15%) and transdermal testosterone, P = 0.066 nor between intramuscular testosterone enantate and undecanoate, P = 0.275.

CONCLUSIONS

One in four individuals treated with intramuscular testosterone enantate and one in six treated with testosterone undecanoate had polycythaemia. No individual treated with transdermal testosterone had polycythaemia. This highlights the importance of regular monitoring of haematocrit in transmasculine individuals treated with testosterone, and findings may inform treatment choices.

Androgen Treatment in Adolescent Males With Hypogonadism

During adolescence, androgens are responsible for the development of secondary sexual characteristics, pubertal growth, and the anabolic effects on bone and muscle mass. Testosterone is the most abundant testicular androgen, but some effects are mediated by its conversion to the more potent androgen dihydrotestosterone (DHT) or to estradiol. Androgen deficiency, requiring replacement therapy, may occur due to a primary testicular failure or secondary to a hypothalamic–pituitary disorder. A very frequent condition characterized by a late activation of the gonadal axis that may also need androgen treatment is constitutional delay of puberty. Of the several testosterone or DHT formulations commercially available, very few are employed, and none is marketed for its use in adolescents. The most frequently used androgen therapy is based on the intramuscular administration of testosterone enanthate or cypionate every 3 to 4 weeks, with initially low doses. These are progressively increased during several months or years, in order to mimic the physiology of puberty, until adult doses are attained. Scarce experience exists with oral or transdermal formulations. Preparations containing DHT, which are not widely available, are preferred in specific conditions. Oxandrolone, a non-aromatizable drug with higher anabolic than androgenic effects, has been used in adolescents with preserved testosterone production, like Klinefelter syndrome, with positive effects on cardiometabolic health and visual, motor, and psychosocial functions. The usual protocols applied for androgen therapy in boys and adolescents are discussed.

Testosterone Therapy and Cardiovascular Risk: A Critical Analysis of Studies Reporting Increased Risk

BACKGROUND

Treatment of "adult-onset hypogonadism" (AOH) with exogenous testosterone therapy (TTh) to raise serum testosterone (T) levels may influence cardiovascular (CV) risk factors in patients with AOH, whereas low endogenous T levels are associated with an increased CV risk and mortality.

AIM

To critically evaluate studies reporting increased CV risk associated with TTh and to provide an overview of the risks and benefits of restoring T levels through exogenous TTh.

METHODS

A review of publications focusing on the association between TTh and increased CV risk was conducted, and the study methodologies and conclusions of each were critically evaluated. Further, recent clinical and epidemiological studies associating AOH or TTh with a change in CV risk, and pertinent hematologic and vascular effects noted in animal studies and in vitro, as well as in clinical practice were also reviewed.

OUTCOMES

A review of the literature shows that untreated testosterone deficiency and/or low T is associated with an increase in CV risk and adverse outcomes, with numerous studies and meta-analyses to support a positive association between exogenous TTh and an improvement in CV risk factors in men with AOH.

RESULTS

Numerous studies in the literature demonstrate the positive benefits of using TTh; however, since 2013, some publications have suggested a link to increased CV risk associated with TTh. A number of these studies retrospectively analyzed insurance claims databases using diagnosis codes, procedures codes, and prescription information. Many reviews published since have pointed out the methodological flaws and debatable conclusions of these studies.

CLINICAL IMPLICATIONS

A careful assessment of the patient's current health status and CV risk factors should be weighed against the benefits and possible risks resulting from TTh, and consideration should be given to deferring treatment pending resolution or stabilization of CV disease or risk factors.

STRENGTHS & LIMITATIONS

In this review, we provide an in-depth analysis of studies reporting increased CV risk with TTh. Many of the studies were not well-designed, randomized, double-blind, prospective clinical trials but rather post hoc analyses of cohort data. These studies may reflect bias in how treatment and nontreatment decisions are made or reflect conclusions based on widely cited methodological flaws.

CONCLUSION

Appropriate patient selection supported by low pre-treatment T levels and monitoring T levels during treatment with the goal of achieving and maintaining physiologic levels all contribute to the safe and effective use of TTh in men with AOH. Khera M, Miner M, Jaffe J, et al. Testosterone Therapy and Cardiovascular Risk: A Critical Analysis of Studies Reporting Increased Risk. J Sex med 2021;18:83-98.

ENDOCRINE HISTORY: The history of discovery, synthesis and development of testosterone for clinical use

As the most important male hormone, testosterone has an impact on almost all organs and body functions. The biological effects of testosterone and the testes have been known since antiquity, long before testosterone was identified as the active agent. Practical applications of this knowledge were castration of males to produce obedient servants, for punishment, for preservation of the prepubertal soprano voice and even for treatment of diseases. Testes were used in organotherapy and transplanted as treatment for symptoms of hypogonadism on a large scale, although these practices had only placebo effects. In reaction to such malpractice in the first half of the 20th century science and the young pharmaceutical industry initiated the search for the male hormone. After several detours together with their teams in 1935, Ernst Laqueur (Amsterdam) isolated and Adolf Butenandt (Gdansk) as well as Leopold Ruzicka (Zürich) synthesized testosterone. Since then testosterone has been available for clinical use. However, when given orally, testosterone is inactivated in the liver, so that parenteral forms of administration or modifications of the molecule had to be found. Over 85 years the testosterone preparations have been slowly improved so that now physiological serum levels can be achieved.

Pharmacokinetic Profile of Subcutaneous Testosterone Enanthate Delivered via a Novel, Prefilled Single-Use Autoinjector: A Phase II Study

INTRODUCTION

Hypogonadism is one of the most common male endocrine problems. Although many treatments are currently available, unmet need exists for new testosterone (T) replacement therapies that are simple to administer and use, are safe, and mimic physiologic T levels.

AIM

The study aim was to determine the pharmacokinetics (PK), safety, and tolerability of T enanthate (TE) administered via a novel single-use autoinjector system, which was designed to eject high-viscosity solutions from a prefilled syringe fitted with a five-eighths-inch 27-gauge needle.

METHODS

Thirty-nine men with hypogonadism entered this dose-finding, open-label, parallel-group study. Patients were washed out of their topical T regimens and randomized to receive 50 or 100 mg of subcutaneous (SC) TE weekly. The reference group were patients with hypogonadism who were maintained on standard 200-mg intramuscular (IM) TE.

MAIN OUTCOME MEASURE

The primary outcome measure was the PK profile of SC TE, analyzed in reference to T levels used by the Food and Drug Administration to approve T products. Secondary outcome measures were safety and tolerability assessments.

RESULTS

Both doses of SC TE achieved normal average concentrations of serum T within a 168-h dosing interval after injection. Concentration ranges were similar at all time points following 50-mg SC TE injections and following the third injection in the 100-mg arm. Mean steady-state T concentration at week 6 was 422.4 and 895.5 ng/dL for the 50- and 100-mg SC TE arms, respectively. SC TE demonstrated PK dose proportionality. SC TE restored normal serum T with low variation relative to 200-mg IM without clinically significant adverse events.

CONCLUSIONS

Administration of TE via this novel injection system restored T levels to normal range in men with hypogonadism. SC TE dosed weekly demonstrated steady, dose-proportional measures of exposure and was well-tolerated. Kaminetsky J, Jaffe JS, Swerdloff RS. Pharmacokinetic profile of subcutaneous testosterone enanthate delivered via a novel, prefilled single-use autoinjector: A phase II study. Sex Med 2015;3:263-273.

Testosterone deficiency: a historical perspective

The biological effects of the testes and testosterone are known since antiquity. Aristotle knew the effects of castration and his hypothesis on fertilization is one of the first scientific encounters in reproductive biology. Over centuries, castration has been performed as punishment and to produce obedient slaves, but also to preserve the soprano voices of prepubertal boys. The Chinese imperial (and other oriental) courts employed castrates as overseers in harems who often obtained high-ranking political positions. The era of testis transplantation and organotherapy was initiated by John Hunter in London who transplanted testes into capons in 1786. The intention of his experiments was to prove the 'vital principle' as the basis for modern transplantation medicine, but Hunter did not consider endocrine aspects. Arnold Adolph Berthold postulated internal secretion from his testicular transplantation experiments in 1849 in Göttingen and is thus considered the father of endocrinology. Following his observations, testicular preparations were used for therapy, popularized by self-experiments by Charles-Edouard Brown-Séquard in Paris (1889), which can at best have placebo effects. In the 1920s Sergio Voronoff transplanted testes from animals to men, but their effectiveness was disproved. Today testicular transplantation is being refined by stem cell research and germ cell transplantation. Modern androgen therapy started in 1935 when Enrest Lacquer isolated testosterone from bull testes in Amsterdam. In the same year testosterone was chemically synthesized independently by Adolf Butenandt in Göttingen and Leopold Ruzicka in Basel. Since testosterone was ineffective orally it was either compressed into subcutaneous pellets or was used orally as 17α-methyl testosterone, now obsolete because of liver toxicity. The early phases of testosterone treatment coincide with the first description of the most prominent syndromes of hypogonadism by Klinefelter, by Kallmann, DelCastillo and Pasqualini. In the 1950s longer-acting injectable testosterone enanthate became the preferred therapeutic modality. In the 1950s and 1960s, research concentrated on the chemical modification of androgens in order to emphasize their anabolic effects. Although anabolic steroids have largely disappeared from clinical medicine, they continue to live an illegal life for doping in athletics. In the 1970s the orally effective testosterone undecanoate was added to the spectrum of preparations. Recent transdermal gels and long-acting injectable preparations provide options for physiological testosterone substitution therapy.

The efficacy and safety of testosterone undecanoate (Nebido(®)) in testosterone deficiency syndrome in Korean: a multicenter prospective study

INTRODUCTION

Long-acting injectable testosterone undecanoate (TU, Nebido(®)), a new parenteral testosterone preparation, has recently been introduced to avoid frequent injections of the conventional injectable esters.

AIMS

To assess the efficacy and safety of long-acting injectable testosterone undecanoate (TU, Nebido(®)) in Korean patients with testosterone deficiency syndrome (TDS).

METHODS

One hundred thirty-three patients who complain of erectile dysfunction with serum testosterone level less than 3.5 ng/mL were injected with 1,000 mg of TU (4 mL/ample) on day 1, followed by another injection after 6 weeks and 18 weeks. For the safety profiles, serum hemoglobin (Hb), hematocrit (Hct), glucose, lipid profile, and prostate-specific antigen (PSA) were measured.

MAIN OUTCOME MEASURES

Body mass index (BMI) was measured at the time of the first visit and after 12, 24 weeks. Primary efficacy was evaluated according to changes in the International Index of Erectile Function (IIEF) from the initial visit to the final visit (24 weeks) and from the initial visit to each visit. Secondary efficacy was assessed with changes of the Aging Males' Symptoms (AMS) Scale and the Global Efficacy Question (GEQ) for improvement of erectile function.

RESULTS

Mean age of patients was 54 ± 9.6 years. Compared with pretreatment, no significant improvement in BMI was observed. Serum total testosterone and free testosterone were significantly increased at 12 weeks and were maintained until 24 weeks (P < 0.001). TU significantly decreased cholesterol (P < 0.0001). TU significantly improved total IIEF, all five domain scores of IIEF (P < 0.0001) and total AMS, all three domain scores of AMS (P < 0.0001). On GEQ, TU improved erectile function in 76.9% of subjects. On safety profile, TU significantly elevated Hb, Hct, and PSA at 24 weeks but within normal range. No serious adverse reactions were observed. Drop-out rate was 15.0%.

CONCLUSIONS

In this prospective multicenter study, TU was effective, safe, and tolerable until 24 weeks in Korean TDS patients. Further well-controlled, long-term study should follow.

Safety and efficacy of testosterone gel in the treatment of male hypogonadism

Transdermal testosterone gels were first introduced in the US in 2000. Since then, they have emerged as a favorable mode of testosterone substitution. Serum testosterone levels reach a steady-state in the first 24 hours of application and remain in the normal range for the duration of the application. This pharmacokinetic profile is comparable to that of testosterone patch but superior to injectable testosterone esters that are associated with peaks and troughs with each dose. Testosterone gels are as efficacious as patches and injectable forms in their effects on sexual function and mood. Anticipated increases in prostate-specific antigen with testosterone therapy are not significantly different with testosterone gels, and the risk of polycythemia is lower than injectable modalities. Application site reactions, a major drawback of testosterone patches, occur less frequently with testosterone gels. However, inter-personal transfer is a concern if appropriate precautions are not taken. Superior tolerability and dose flexibility make testosterone gel highly desirable over other modalities of testosterone replacement. Androgel and Testim, the two currently available testosterone gel products in the US, have certain brand-specific properties that clinicians may consider prior to prescribing.

Critical factors influencing the in vivo performance of long-acting lipophilic solutions--impact on in vitro release method design

Parenteral long-acting lipophilic solutions have been used for decades and might in the future be used in the design of depots with tailored delivery characteristics. The present review highlights major factors influencing the in vivo performance of lipophilic solutions. Furthermore, an account is given of the characteristics of employed in vitro release methods with a focus on the "state" of sink condition, the stirring conditions, and the oil-water interfacial area. Finally, the capability of in vitro release data to predict the in vivo performance of drug substances administrated in the form of lipophilic solutions is discussed. It is suggested that as long as the major rate-limiting in vivo release mechanism is governed by the drug partitioning between the oil vehicle and the tissue fluid, the use of in vitro release testing in quality control appears to be realistic. With increasing lipophilicity of the drug substances and longer duration of action, the in vivo drug release process may become more complex. As discussed, practical analytical problems together with the inability of release methods to mimic two or more concomitant in vivo events may constitute severe impediments for establishment of in vitro in vivo correlations.

Multicenter contraceptive efficacy trial of injectable testosterone undecanoate in Chinese men

CONTEXT

Hormonal male contraceptive regimens effectively and reversibly suppress sperm production, but there are few large-scale efficacy studies.

OBJECTIVE

The safety, contraceptive efficacy, reversibility, and feasibility of injectable testosterone undecanoate (TU) in tea seed oil as a hormonal male contraceptive was assessed.

DESIGN

This was a multicenter, phase III, contraceptive efficacy clinical trial.

PARTICIPANTS

A total of 1045 healthy fertile Chinese men were recruited throughout China into the study.

INTERVENTION(S)

Injections of 500 mg TU were administered monthly for 30 months. A definition of severe oligozoospermia (< or =1 x 10(6)/ml) was used as a criterion of spermatogenic suppression and as the threshold for entering the contraceptive efficacy phase.

MAIN OUTCOME MEASURE(S)

The primary outcome was pregnancy rate in the partner. Other outcomes include: semen parameters, testis volumes, reproductive hormone levels, and safety laboratory tests.

RESULTS

Forty-three participants (4.8%) did not achieve azoospermia or severe oligozoospermia within the 6-month suppression phase. A total of 855 participants entered into the efficacy phase, and 733 participants completed monthly TU treatment and follow-up. There were nine pregnancies in 1554.1 person-years of exposure in the 24-month efficacy phase for a cumulative contraceptive failure rate of 1.1 per 100 men. The combined method failure rate was 6.1%, comprising 4.8% with inadequate suppression and 1.3% with postsuppression sperm rebound. No serious adverse events were reported. Spermatogenesis returned to the normal fertile reference range in all but two participants.

CONCLUSIONS

Monthly injection of 500 mg TU provides safe, effective, reversible, and reliable contraception in a high proportion of healthy fertile Chinese men.

More than eight years' hands-on experience with the novel long-acting parenteral testosterone undecanoate

Testosterone (T) as a compound for treatment of T deficiency has been available for almost 70 years, but the pharmaceutical formulations have been less than ideal. Traditionally, injectable T esters have been used for treatment, but they generate supranormal T levels shortly after the 2-3 weekly injection interval. T levels then decline very rapidly, becoming subnormal during the days preceding the next injection. The rapid fluctuations in plasma T are subjectively experienced as disagreeable. T undecanoate (TU) is a new injectable T preparation with a considerably better pharmacokinetic profile. After two initial injections separated by a 6-week interval, the following intervals between two injections are generally 12 weeks, eventually amounting to a total of four injections per year. Plasma T levels with this preparation are nearly always in the range of normal men, as are its metabolic products estradiol and dihydrotestosterone (DHT). It reverses the effects of hypogonadism on bone and muscle and metabolic parameters, and on sex functions. It is suitable for male contraception. Its safety profile is excellent because of the continuous normalcy of plasma T levels. No polycythemia has been observed and no adverse effects on lipid profiles. Prostate safety parameters are well within reference limits. TU is a valuable treatment option of androgen deficiency.

Testosterone treatment comes of age: new options for hypogonadal men

Male hypogonadism is one of the most frequent, but also most underdiagnosed, endocrinopathies. However, the required testosterone treatment is simple and very effective if properly administered. Although testosterone has been available for clinical use for seven decades, until quite recently the treatment modalities were far from ideal. Subdermal testosterone pellets require minor surgery for insertion and often cause local problems. The injectable testosterone enanthate, for a long period the most frequently used mode of administration, lasts for two to four weeks, but produces supraphysiological levels initially and low levels before the next injection. The oral testosterone undecanoate has to be taken three times daily, has an uncertain absorption pattern and results in peaks and valleys of serum testosterone levels throughout the day. With the advent of transdermal testosterone preparations, the desired physiological serum levels could be achieved for the first time. Scrotal testosterone patches were the first to fulfil this requirement. These were followed by nonscrotal skin patches, which, however, cause considerable skin reactions including erythema and blisters. Recently introduced, invisible transdermal testosterone gels increased the intervals of application and are now slowly replacing other modalities. A mucoadhesive buccal testosterone tablet with sustained release is also a recent competing modality. Finally, injectable testosterone undecanoate in castor oil was made into a real depot preparation requiring only four injections per year for replacement therapy. These new preparations with a desired pharmacokinetic testosterone profile give the patient a real choice and make treatment easier. Based on pharmacogenetic considerations taking the androgen receptor polymorphism into account, treatment may be individualized for each patient in the future.

Testosterone Hormone Replacement Therapy: State-of-the-Art and Emerging Technologies

In the human male, testosterone is the major circulating androgen. The clinical effects of androgen are numerous, and testosterone deficiency is associated with a number of clinical abnormalities. At present, a variety of preparations containing testosterone is available for the treatment of androgen deficiency. Ideally, those treatments have to produce and maintain physiologic serum concentrations of the hormone. This article reviews the current existing testosterone dosage forms on the market with their advantages and drawbacks and examines new and emerging technology developments concerning this therapy. In particular, the latest innovations in transdermal delivery are explored.

Nebido: a long-acting injectable testosterone for the treatment of male hypogonadism

Over the last six decades, tremendous strides have been made in the development of safe, efficacious and 'patient-friendly' modalities of testosterone replacement therapy in men. The most recent forms of androgen replacement that are in widespread use include testosterone patch and gel. These preparations are convenient in their use and deliver a physiological amount of testosterone. Although these transdermal preparations are gaining popularity, many hypogonadal men still receive treatment with intramuscular esters. Testosterone enanthate remains the most commonly prescribed ester. Although testosterone esters are efficacious in terms of improving bone and muscle mass, they possess unfavourable pharmacokinetics that result in fluctuations in the mood, energy and sexual function of patients. Furthermore, these esters need to be injected every 2-4 weeks. Hence, there has been a need to develop long-acting esters that can be administered infrequently and deliver a physiological amount of testosterone without major fluctuations. Recently, injectable testosterone undecanoate (Nebido) has become available in Europe and will soon be marketed in south America, Asia and Australia. In this paper, the structure, pharmacokinetics, efficacy and side-effect profile of testosterone undecanoate will be reviewed and also compared with other existing testosterone esters.

Pharmacokinetics and pharmacodynamics of injectable testosterone undecanoate in castrated cynomolgus monkeys (Macaca fascicularis) are independent of different oil vehicles

Testosterone undecanoate (TU) dissolved in soybean oil was developed in China to improve the pharmacokinetics of this testosterone ester in comparison with TU in castor or tea seed oil. As a pre-clinical primate model, three groups of five castrated cynomolgus macaques received either a single intramuscular injection of 10 mg/kg body weight TU in soybean oil, in tea seed oil, or in castor oil (equals 6.3 mg pure T/kg body weight for all preparations). Testosterone, estradiol, luteinizing hormone, and follicle-stimulating hormone as well as prostate volume, body weight and ejaculate weight were evaluated. After injection supraphysiological testosterone levels were induced. There were no significant differences in the pharmacokinetics of the three TU preparations for testosterone and estradiol. The gonadotropin levels showed a high individual variation. Prostate volumes increased equally in all groups after administration and declined to castrate level afterwards. The results suggest that TU in soybean oil produces similar effects as TU in the other vehicles. This study in non-human primates provides no objection to testing of this new preparation in humans.

Pharmacokinetics and degree of aromatization rather than total dose of different preparations determine the effects of testosterone: a nonhuman primate study in Macaca fascicularis

Currently available testosterone (T) preparations differ substantially in their pharmacokinetic profile that might influence their androgenic properties in terms of suppression of the gonadal axis, effects on anabolic parameters, lipid metabolism, and erythropoiesis. The present work was undertaken to determine the physiological effects of three T preparations with different serum kinetics. Twenty adult male cynomolgus monkeys (Macaca fascicularis) were randomly assigned to receive treatment for 28 weeks with either T enanthate (TE) every 4 weeks, T buciclate (TB) every 7 weeks, or T undecanoate (TU) every 10 weeks or remaining untreated (controls). Each injection delivered 20 mg pure T per kilogram body weight. Pharmacokinetic profiles demonstrated higher peak levels of T for TE-treated animals; serum half-lives were longer for TU or TB. Estradiol levels (area under the curve) were significantly higher in TB vs TU or TE. All T regimens suppressed serum luteinizing hormone bioactivity and testicular volumes declined (all P <.001 vs controls). Sperm counts were markedly lowered in all animals but least in TE (P <.01 vs TB or TU). During recovery phase, return to normal for all three parameters occurred significantly earlier in TE-treated animals, followed by those given TU, compared with TB (all P <.001 between groups). Body weight increased significantly during T exposure. This effect was stronger and more sustained in TB vs TU or TE (both P <.001). Serum creatinine and hemoglobin increased with high significance in all T-treated animals (all P <.001 vs controls). The lowering impact of T on serum lipids was markedly stronger in the longer-acting T preparations in comparison with TE, as were effects on purine metabolism (all P <.001). The pattern of exposure and degree of aromatization rather than overall exposure to T determine its effects in the preclinical primate model. Both fluctuations of androgen concentrations and the conversion rate to estradiol influence gonadal suppression as well as metabolism. These results have to be considered in men receiving treatment for hypogonadism or regimens for hormonal contraception.

Androgens and puberty

Puberty is associated with an increasing production of androgenic steroids. Adrenal androgen formation, termed adrenarche, may precede gonadal testosterone synthesis. Both adrenal and gonadal androgens exert their biological effects via the androgen receptor, a nuclear transcription factor modulating a specific transcription regulation of largely unknown genes. During puberty, virilizing actions such as genital enlargement and sexual hair growth can be distinguished from anabolic action such as the gain in muscle strength and general changes in body composition. Furthermore, androgens play a major role in the initiation and maintenance of spermatogenesis. Thus, different androgenic steroids play an important role in the process of puberty. The control of their biosynthesis, their possible differential action on the molecular level, as well as the different target organs in males and females are discussed.

Intramuscular testosterone undecanoate with or without oral levonorgestrel: a randomized placebo-controlled feasibility study for male contraception

OBJECTIVE

Approaches to hormonal male contraception are based on injectable testosterone esters alone or in combination with gestagens or GnRH analogs but the short half-life of clinically used testosterone esters have long hindered further development. This study was designed to prove the efficacy of the long-acting testosterone undecanoate ester (TU) alone or in combination with oral levonorgestrel (LNG) in a phase II clinical trial.

DESIGN AND SUBJECTS

Twenty-eight healthy men were randomized to receive injections of 1000 mg TU every 6 weeks in combination with daily oral LNG (250 microg) or daily oral placebo treatment over a period of 24 weeks, followed by a control period of 28 weeks.

MEASUREMENTS

During the course of the study semen analysis, reproductive hormone analysis, analysis of clinical chemistry and lipid parameters, well-being and sexual function, sonography of scrotal contents and prostate were performed.

RESULTS

Marked suppression of gonadotrophins in both treatment groups resulted in azoospermia in 8/14 and 7/14 volunteers and severe oligozoospermia (< 3 x 1012/l) in 4/14 and 7/14 in the placebo and gestagen treated groups, respectively. Time to induction of azoospermia (mean +/- SEM) was not significantly different between the placebo (week 19.5 +/- 2.2) and LNG groups (week 15.4 +/- 2.2). During the whole treatment period mean testosterone serum concentrations remained within normal limits. Although not significant, it was evident that volunteers who became azoospermic had a better suppression of gonadotrophins and lower SHBG levels during treatment compared to non-azoospermic volunteers. Despite better gonadotrophin suppression in the LNG group no significant differences compared to placebo could be observed in the extent and kinetics of suppression of spermatogenesis, thus not demonstrating a major beneficial effect of LNG in the combination with injectable TU. Treatment led in both groups to a decrease of HDL and Lp(a) which was more pronounced in the LNG group (P > 0.05).

CONCLUSION

Treatment with 1000 mg testosterone undecanoate injected at 6 weekly intervals or in combination with levonorgestrel showed suppression of spermatogenesis comparable to weekly injections of 200 mg testosterone enanthate. Because of its long half-life and in the absence of severe side-effects, testosterone undecanoate can be considered as first choice testosterone ester in further studies of hormonal male contraception.

Hormone substitution in male hypogonadism

Male hypogonadism is characterised by androgen deficiency and infertility. Hypogonadism can be caused by disorders at the hypothalamic or pituitary level (hypogonadotropic forms) or by testicular dysfunction (hypergonadotropic forms). Testosterone substitution is necessary in all hypogonadal patients, because androgen deficiency causes slight anemia, changes in coagulation parameters, decreased bone density, muscle atrophy, regression of sexual function and alterations in mood and cognitive abilities. Androgen replacement comprises injectable forms of testosterone as well as implants, transdermal systems, sublingual, buccal and oral preparations. Transdermal systems provide the pharmacokinetic modality closest to natural diurnal variations in testosterone levels. New injectable forms of testosterone are currently under clinical evaluation (testosterone undecanoate, testosterone buciclate), allowing extended injection intervals. If patients with hypogonadotropic hypogonadism wish to father a child, spermatogenesis can be initiated and maintained by gonadotropin therapy (conventionally in the form of human chorionic gonadotropin (hCG) and human menopausal gonadotropin (hMG) or, more recently, purified or recombinant follicle stimulating hormone (FSH)). Apart from this option, patients with disorders at the hypothalamic level can be stimulated with pulsatile gonadotropin-releasing hormone (GnRH). Both treatment modalities have to be administered on average for 7-10 months until pregnancy is achieved. In individual cases, treatment may be necessary for up to 46 months. Testosterone treatment is interrupted for the time of GnRH of gonadotropin therapy, but resumed after cessation of this therapy.

Testosterone therapy in men: clinical and pharmacological perspectives

There is increasing evidence that androgen therapy in men may be effectively applied in several conditions to improve well being and health. Classical indications for androgen therapy in males are represented by primary or secondary hypogonadism, delayed puberty, aplastic anemia and that secondary to chronic renal failure, protein wasting diseases such as trauma, burns, tumors and infectious diseases. Androgen innovating applications in men are represented by aging and visceral obesity associated with the metabolic syndrome. In addition, it is clear that appropriate testosterone treatment can be adequately used in male contraception, provided spermatogenesis is abolished and tolerability is adequate. Due to unphysiological hormone levels achieved by currently available testosterone preparations, new delivery systems have been produced to achieve more physiological and sustained hormone levels and improve tolerability and action at the levels of target tissues. Some of them are now available in several countries and new formulas are under development.

Repeated intramuscular injections of testosterone undecanoate for substitution therapy in hypogonadal men

OBJECTIVE

To investigate the suitability of intramuscular testosterone undecanoate (TU) injections for substitution therapy in hypogonadal men.

STUDY DESIGN

Clinical, open-label, non-randomized trial of 13 hypogonadal men receiving 4 intramuscular injections of 1000 mg TU in 4-ml castor oil at 6-week intervals. General wellbeing, sexual parameters, clinical chemistry, hormone levels, prostate size and prostate-specific antigen (PSA) were evaluated over 24 weeks and compared with baseline values.

RESULTS

Testosterone serum levels were never found below the lower limit of normal and only briefly after the 3rd and 4th injection above the upper limit of normal, while peak and trough values increased over the 24-week observation period. Oestradiol and dihydrotestosterone followed this pattern, not exceeding the normal limits. No serious side-effects were noted. Slight increases in body weight, haemoglobin, haematocrit, prostate volume and PSA, suppression of gonadotrophins as well as increased ejaculation frequency occurred as signs of adequate testosterone substitution.

CONCLUSION

Testosterone undecanoate is well tolerated by the patients. The injection intervals can be extended even beyond the 6-week periods chosen in the present study. Altogether, intramuscular testosterone undecanoate appears to be well suited for long-term substitution therapy in hypogonadism and hormonal male contraception.

Male hormone replacement therapy including "andropause"

Adult onset male hypogonadism and the testosterone deficiency of the aging male often are under-recognized entities. The etiologies, presentation, and diagnosis of hypogonadism and andropause in the adult male are presented. The expected therapeutic goals, potential treatment risks, and management of androgen replacement therapy for the adult man are reviewed. The advantages and disadvantages of the various androgen delivery systems currently available and under investigation are discussed.

Testosterone replacement therapy

The benefits conferred by testosterone replacement therapy are substantial, both in the short term for the eradication of symptoms of androgen deficiency, and in the long term for the prevention of osteoporosis. As with any long-term treatment there are risks that must be considered, but overall the benefits achieved far outweigh potential risk. Ideally, androgen replacement therapy should provide physiological serum testosterone levels, as well as DHT and estradiol levels, and correct the clinical symptoms of androgen deficiency in hypogonadal men. This goal is difficult to achieve because the dose dependency of androgen-dependent physiological processes is not known. Androgen preparations that are currently available do not fulfill all criteria for an ideal androgen replacement therapy. Parenteral testosterone esters are effective, safe, practical, and inexpensive. The transdermal testosterone systems provide an alternative to testosterone esters in selected patients but these preparations are expensive. Ongoing studies are showing the benefits of testosterone replacement therapy in aging men, but there is concern about side effects on cardiovascular system and prostate. Thus, clinical decision regarding testosterone therapy in older men should be better defined.