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Testosterone undecanoate, is an androgen and anabolic steroid (AAS) medication which is used mainly in the treatment of low testosterone levels in men. It is also used in hormone therapy for transgender men. It is taken by mouth two to three times per day with food or given by injection into muscle once every 12 weeks or so.
Side effects of testosterone undecanoate include symptoms of masculinization like acne, increased hair growth, voice changes, and increased sexual desire. The drug is a synthetic androgen and anabolic steroid and hence is an agonist of the androgen receptor (AR), the biological target of androgens like testosterone and dihydrotestosterone (DHT). It has strong androgenic effects and moderate anabolic effects, which make it useful for producing masculinization and suitable for androgen replacement therapy. Testosterone undecanoate is a testosterone ester and a prodrug of testosterone in the body. Because of this, it is considered to be a natural and bioidentical form of testosterone.
Testosterone undecanoate was introduced in China for use by injection and in Europe for use by mouth in the 1970s. It became available for use by injection in Europe in the early to mid 2000s and in the United States in 2014. A formulation for use by mouth is not currently available in the United States but is pending approval as of 2018. Along with testosterone enanthate, testosterone cypionate, and testosterone propionate, testosterone undecanoate is one of the most widely used testosterone esters. However, it has advantages over other testosterone esters in that it can be taken by mouth and in that it has a far longer duration when given by injection. In addition to its medical use, testosterone undecanoate is used to improve physique and performance. The drug is a controlled substance in many countries and so non-medical use is generally illicit.
Testosterone undecanoate is used in androgen replacement therapy. It is specifically approved only for the treatment of hypogonadism. As an intramuscular injection, it is administered at a dosage of 1,000 mg once every 12 weeks. Conversely, oral testosterone undecanoate must be taken two or three times a day with food.
The Reandron 1000 formulation (Nebido in the United States) contains 1,000 mg of testosterone undecanoate suspended in castor oil with benzyl benzoate for solubilization and as a preservative, and is administered by intramuscular injection. As an excipient, benzyl benzoate has been reported as a cause of anaphylaxis in a case in Australia. Bayer includes this report in information for health professionals and recommends that physicians “should be aware of the potential for serious allergic reactions” to preparations of this type. In Australia, reports to ADRAC, which evaluates reports of adverse drug reactions for the Therapeutic Goods Administration, show several reports of allergic issues since the anaphylaxis case from 2011.
Testosterone undecanoate has a very long elimination half-life and mean residence time when given as a depot intramuscular injection. Its elimination half-life is 20.9 days and its mean residence time is 34.9 days in tea seed oil, while its elimination half-life is 33.9 days and its mean residence time is 36.0 days in castor oil. These values are substantially longer than those of testosterone enanthate (which, in castor oil, has values of 4.5 days and 8.5 days, respectively). Testosterone undecanoate is administered via intramuscular injection once every three months or so.
Testosterone undecanoate, or testosterone 17β-undecanoate, is a synthetic androstane steroid and a derivative of testosterone. It is an androgen ester; specifically, it is the C17β undecylate (undecanoate) ester of testosterone. A related testosterone ester with a similarly very long duration is testosterone buciclate.
In the late 1970s, testosterone undecanoate was introduced for oral use in Europe, although intramuscular testosterone undecanoate had already been in use in China for several years. Intramuscular testosterone undecanoate was not introduced in Europe and the United States until much later, in the early to mid 2000s and 2014, respectively. Testosterone undecanoate was approved in the United States after three previous rejections due to safety concerns.