Pharmacokinetics
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. Chemistry
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. History
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. Society and culture
Generic names
Testosterone undecanoate is the generic name of the drug and its USAN and BAN. It is also referred to as testosterone undecylate.
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. Medical dosage
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. Side effects
Side effects of testosterone undecanoate include virilization among others. Anaphylaxis
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 in Reandron 1000, benzyl benzoate has been reported as a cause of anaphylaxis (a serious life-threatening allergic reaction) 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 the Adverse Drug Reactions Advisory Committee (ADRAC), which evaluates reports of adverse drug reactions for the Therapeutic Goods Administration (TGA), show several reports of allergic reactions since the anaphylaxis case from 2011. Pharmacology
Pharmacodynamics
Testosterone undecanoate is a prodrug of testosterone and is an androgen and anabolic–androgenic steroid (AAS). That is, it is an agonist of the androgen receptor (AR).